View source for Hydroponics

{{Short description|Growing plants without soil using nutrients in water}}
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{{Wiktionary | hydroponics}}

[[File:Hydroponic onions, NASA -- 17 June 2004.jpg|thumb|275x275px|[[NASA]] researcher Ray Wheeler checking hydroponic [[onion]]s (center), [[Bibb lettuce]]s (left), and [[radish]]es (right)|alt=]]
{{Agriculture}}

'''Hydroponics''' is a type of [[horticulture]] and a subset of [[#Passive sub-irrigation|hydroculture]] which involves growing [[plant]]s, usually [[crops]] or [[medicinal plants]], without [[soil]], by using water-based [[mineral]] [[Plant nutrition|nutrient]] [[Solution (chemistry)|solution]]s in an artificial environment. [[Terrestrial plant|Terrestrial]] or [[aquatic plant]]s may grow freely with their [[root]]s exposed to the nutritious liquid or the roots may be mechanically supported by an inert medium such as [[perlite]], [[gravel]], or [[#Substrates (growing support materials)|other substrates]].<ref>{{Cite journal |last= Gericke |first= William F. |date= 1945 |title= The meaning of hydroponics |journal= Science |volume= 101|issue= 2615 |pages= 142–143 |doi= 10.1126/science.101.2615.142 |pmid= 17800488 |bibcode= 1945Sci...101..142G}}</ref>

Despite inert media, roots can cause changes of the [[rhizosphere]] [[pH]] and [[root exudate]]s can affect rhizosphere biology and physiological balance of the nutrient solution when [[secondary metabolite]]s are produced in plants.<ref>{{cite journal |last1=Nye |first1=P. H. |title=Changes of pH across the rhizosphere induced by roots |journal=Plant and Soil |date=February 1981 |volume=61 |issue=1–2 |pages=7–26 |doi=10.1007/BF02277359 |bibcode=1981PlSoi..61....7N }}</ref><ref>{{Cite journal|last1= Walker|first1= T. S.|last2= Bais|first2= H. P.|last3= Grotewold|first3= E.|last4= Vivanco|first4= J. M.|date= 2003|title= Root exudation and rhizosphere biology|journal= Plant Physiology|volume= 132|issue= 1|pages= 44–51|doi= 10.1104/pp.102.019661|pmid= 12746510|pmc= 1540314|doi-access= free}}</ref><ref name="Suryawanshi Hydroponic Cultivation">{{cite book |doi=10.1201/9781003034957-5 |chapter=Hydroponic Cultivation Approaches to Enhance the Contents of the Secondary Metabolites in Plants |title=Biotechnological Approaches to Enhance Plant Secondary Metabolites |date=2021 |last1=Suryawanshi |first1=Yogesh Chandrakant |pages=71–88 |isbn=978-1-003-03495-7 }}</ref> [[Genetically modified plant|Transgenic plants]] grown hydroponically allow the release of [[Pharming (genetics)#In plants|pharmaceutical proteins]] as part of the root exudate into the hydroponic medium.<ref>{{cite journal|author1=Horn, M.E. |author2=Woodard, S.L. |author3=Howard, J.A. |title=Plant molecular farming: systems and products |journal=Plant Cell Reports |volume=22 |issue=10 |pages=711–720|doi=10.1007/s00299-004-0767-1|year=2004|pmid=14997337 |pmc=7079917 |doi-access=free|bibcode=2004PCelR..22..711H }}</ref>

The nutrients used in [[#Techniques|hydroponic systems]] can come from many different [[Organic matter|organic]] or [[Inorganic compound|inorganic]] sources, including [[fish excrement]], [[duck]] [[manure]], purchased [[chemical fertilizer]]s, or artificial [[Dennis Robert Hoagland#Standard nutrient solutions|standard]] or [[Dennis Robert Hoagland#Hybrid nutrient solutions|hybrid]] nutrient solutions.{{sfn|Jones Jr.|2016|pp=153–166}}

In contrast to field cultivation, plants are commonly grown hydroponically in a [[greenhouse]] or [[Growroom|contained environment]] on inert media, adapted to the [[controlled-environment agriculture]] (CEA) process.<ref name=":-2">{{Cite news|url= https://psci.princeton.edu/tips/2020/11/9/the-future-of-farming-hydroponics|title= The future of farming: hydroponics|work= PSCI|access-date= Aug 25, 2022|language= en-US}}</ref> Plants commonly grown hydroponically include [[tomatoes]], [[Capsicum|peppers]], [[cucumbers]], [[Strawberry|strawberries]], [[lettuces]], and [[cannabis]], usually for commercial use, as well as ''[[Arabidopsis thaliana]]'', which serves as a [[model organism]] in [[botany|plant science]] and [[genetics]].<ref>{{Cite news|url= https://bio-protocol.org/bio101/e3121|title= A simplified hydroponic culture of ''Arabidopsis''|work= Bio-101|access-date= Mar 4, 2020|language= en-US}}</ref>

Hydroponics offers many advantages, notably a decrease in water usage in agriculture. To grow {{convert|1|kg}} of tomatoes using

* [[intensive farming]] methods requires {{convert|214|liter}} of water;<ref>{{Cite news|url= https://www.theguardian.com/news/datablog/2013/jan/10/how-much-water-food-production-waste|title= How much water is needed to produce food and how much do we waste?|work= The Guardian|access-date= Aug 19, 2022|language= en-US}}</ref> 
* using hydroponics, {{convert|70|liter}}; and 
* only {{convert|20|liter}} using [[aeroponics]].<ref>{{cite journal |last1=Zhang |first1=He |last2=Asutosh |first2=Ashish |last3=Hu |first3=Wei |title=Implementing Vertical Farming at University Scale to Promote Sustainable Communities: A Feasibility Analysis |journal=Sustainability |date=27 November 2018 |volume=10 |issue=12 |page=4429 |doi=10.3390/su10124429 |doi-access=free |bibcode=2018Sust...10.4429Z }}{{rs|The paper describes the authors statistical concept modeling in determining the potential advantages of developing a vertical farm at Huazhong University of Science and Technology. While the figures are conservative and project the farm's profitability in 10 to 20 years, it is based on metadata and not on direct observation.|date=March 2025}}</ref>

Hydroponic cultures lead to highest [[Biomass (ecology)|biomass]] and [[protein]] production compared to other [[Substrate (biology)|growth substrates]], of plants cultivated in the same [[Biophysical environment|environmental conditions]] and supplied with equal amounts of nutrients.<ref name=":-3">{{cite journal|author1=Nagel, K.A. |author2=Kastenholz, B. |author3=Gilmer, F. |author4=Schurr, U. |author5=Walter, A. |title=Novel detection system for plant protein production of pharmaceuticals and impact on conformational diseases |journal=Protein and Peptide Letters |volume=17 |issue=6 |pages=723–731|doi=10.2174/092986610791190282|pmid=20015023|year=2010}}</ref>

Hydroponics is not only used on earth, but has also proven itself in plant production experiments in [[low Earth orbit|Earth orbit]].<ref>{{cite book |doi=10.2514/6.2011-5263 |chapter=Concept for Sustained Plant Production on ISS Using VEGGIE Capillary Mat Rooting System |title=41st International Conference on Environmental Systems |date=2011 |last1=Stutte |first1=Gary |last2=Wheeler |first2=Raymond |last3=Morrow |first3=Robert |last4=Newsham |first4=Gerard |isbn=978-1-60086-948-8 |hdl=2060/20110011606 |hdl-access=free }}</ref>

== History ==
[[File:Hydro system.jpg|thumb|Inside an ebb-and-flow hydroponic system employing individual buckets connected by fill/drain hoses.]]
The earliest published work on growing terrestrial plants without soil was the 1627 book ''Sylva Sylvarum'' or 'A Natural History' by [[Francis Bacon]], printed a year after his death. As a result of his work, water culture became a popular research technique. In 1699, [[John Woodward (naturalist)|John Woodward]] published his water culture experiments with [[spearmint]]. He found that plants in less-pure water sources grew better than plants in distilled water.<ref>{{cite journal |last=Woodward |first=John |year=1699 |title=Some thoughts and experiments concerning vegetation |url=https://royalsocietypublishing.org/doi/10.1098/rstl.1699.0040 |journal=Philosophical Transactions of the Royal Society |volume=21 |issue=253 |pages=193–227 |doi=10.1098/rstl.1699.0040}}</ref> By 1842, a list of nine elements believed to be essential for plant growth had been compiled, and the discoveries of German botanists [[Julius von Sachs]] and [[Wilhelm Knop]], in the years 1859–1875, resulted in a development of the technique of soilless cultivation.{{sfn|Douglas|1975|pp=1–3}} To quote von Sachs directly: ''"In the year 1860, I published the results of experiments which demonstrated that [[Embryophyte|land plants]] are capable of absorbing their nutritive matters out of watery solutions, without the aid of soil, and that it is possible in this way not only to maintain plants alive and growing for a long time, as had long been known, but also to bring about a vigorous increase of their organic substance, and even the production of seed capable of [[germination]]."''<ref>{{cite book |last1=Sachs |first1=Julius |title=Lectures on the Physiology of Plants |date=1887 |publisher=Clarendon Press |page=283 |url=https://books.google.com/books?id=ZLvPAAAAMAAJ&dq=%22In%20the%20year%201860%2C%20I%20published%20the%20results%20of%20experiments%20which%20demonstrated%20that%20land%20plants%20are%20capable%20of%20absorbing%20their%20nutritive%20matters%20out%20of%20watery%20solutions%2C%20without%20the%20aid%20of%20soil%2C%20and%20that%20it%20is%20possible%20in%20this%20way%20not%20only%20to%20maintain%20plants%20alive%20and%20growing%20for%20a%20long%20time%2C%20as%20had%20long%20been%20known%2C%20but%20also%20to%20bring%20about%20a%20vigorous%20increase%20of%20their%20organic%20substance%2C%20and%20even%20the%20production%20of%20seed%20capable%20of%20germination.%22&pg=PA283 }}</ref> Growth of terrestrial plants without soil in mineral nutrient solutions was later called "solution culture" in reference to "soil culture". It quickly became a standard research and teaching technique in the 19th and 20th centuries and is still widely used in [[plant nutrition]] science.<ref>{{Cite journal|last=Breazeale|first=J. F.|date=1906|title=The relation of sodium to potassium in soil and solution cultures|journal=Journal of the American Chemical Society|volume=28|issue=8|pages=1013–1025|doi=10.1021/ja01974a008|bibcode=1906JAChS..28.1013B |url=https://zenodo.org/record/1887883}}</ref>

Around the 1930s plant nutritionists investigated [[Plant pathology|diseases]] of certain plants, and thereby, observed symptoms related to existing soil conditions such as [[Soil salinity|salinity]] or nutrient deficiency. In this context, water culture experiments were undertaken with the hope of delivering similar symptoms under controlled laboratory conditions.<ref>{{cite journal|title=Nutrition of strawberry plant under controlled conditions. (a) Effects of deficiencies of boron and certain other elements, (b) susceptibility to injury from sodium salts|last1=Hoagland |first1=D.R. |last2=Snyder |first2=W.C.|journal=Proceedings of the American Society for Horticultural Science|year=1933|volume=30|pages=288–294}}</ref> This approach forced by [[Dennis Robert Hoagland]] led to innovative model systems (e.g., [[green algae]] [[Nitella]]) and [[Dennis Robert Hoagland#Hewitt's Table 30A|standardized nutrient recipes]] playing an increasingly important role in modern [[plant physiology]].<ref name=":nas">{{cite web|title=Dennis Robert Hoagland: 1884-1949|work=Biographical Memoirs of the National Academy of Sciences|url=https://www.nasonline.org/directory-entry/dennis-r-hoagland-lmtdrd/|access-date=13 July 2025}}</ref> In 1929, [[William Frederick Gericke]] of the University of California at Berkeley began publicly promoting that the principles of solution culture be used for [[agriculture|agricultural crop production]].<ref>{{Cite journal|last= Gericke|first= William F.|date= 1929|title= Aquiculture - a means of crop production|journal= American Journal of Botany|volume= 16|pages= 862–867}}</ref><ref>{{Cite journal|last=Dunn|first=H. H.|date=October 1929|title=Plant "Pills" Grow Bumper Crops|url=https://books.google.com/books?id=VigDAAAAMBAJ&pg=PA29|journal=[[Popular Science|Popular Science Monthly]]|pages=29–30}}</ref><ref>{{Cite journal|last1=Thiyagarajan|first1=G.|last2=Umadevi|first2=R.|last3=Ramesh|first3=K.|date=Jan 2007|title=Hydroponics|url=http://www.techno-preneur.net/information-desk/sciencetech-magazine/2007/jan07/Hydroponics.pdf|journal=Science Tech Entrepreneur|archive-url=https://web.archive.org/web/20091229051310/http://www.techno-preneur.net/information-desk/sciencetech-magazine/2007/jan07/Hydroponics.pdf|archive-date=December 29, 2009|via=[[Wayback Machine]]}}</ref> He first termed this cultivation method "aquiculture" created in analogy to "agriculture" but later found that the cognate term [[aquaculture]] was already applied to culture of [[Aquatic animal|aquatic organisms]]. Gericke created a sensation by growing tomato vines {{convert|25|ft|m|abbr=off|spell=in}} high in his backyard in mineral nutrient solutions rather than soil.<ref>{{Cite news|url=https://home.howstuffworks.com/lawn-garden/professional-landscaping/hydroponics.htm|title=How Hydroponics Works|last=Turner|first=Bambi|date=Oct 20, 2008|work=HowStuffWorks|access-date=May 29, 2012|publisher=InfoSpace Holdings LLC|language=en}}</ref> He then introduced the term ''Hydroponics'', water culture, in 1937, proposed to him by [[:es:William Albert Setchell|W. A. Setchell]], a [[phycology|phycologist]] with an extensive education in the classics.<ref name=":-1">{{Cite journal |last=Gericke |first=William F. |date=1937 |title=Hydroponics - crop production in liquid culture media |journal=Science |volume=85 |issue=2198 |pages=177–178 |bibcode=1937Sci....85..177G |doi=10.1126/science.85.2198.177 |pmid=17732930}}</ref><ref>{{cite web|url=http://ucjeps.berkeley.edu/setchell.html|title=Biography of W.A. Setchell|publisher=The University and Jepson Herbaria, University of California|archive-url=https://web.archive.org/web/20151015233655/http://ucjeps.berkeley.edu/setchell.html|archive-date=October 15, 2015|access-date=Nov 21, 2018}}</ref> Hydroponics is derived from [[neologism]] υδρωπονικά (derived from Greek ύδωρ=water and πονέω=cultivate), constructed in analogy to γεωπονικά (derived from Greek γαία=earth and πονέω=cultivate),<ref>{{cite web|url=https://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.04.0057:entry=gewponiko/s|title=A Greek-English Lexicon|last1=Liddell|first1=H. G.|last2=Scott|first2=R.|website=www.perseus.tufts.edu|access-date=Nov 21, 2018}}</ref> [[geoponica]], that which concerns agriculture, replacing, γεω-, earth, with ὑδρο-, water.{{sfn|Douglas|1975|pp=1–3}}

Despite initial successes, however, Gericke realized that the time was not yet ripe for the general [[Technology|technical application]] and [[Commerce|commercial use]] of hydroponics for producing crops.<ref>{{cite web|url=https://youtube.com/watch?v=foRUrxkx2MU/| archive-url=https://ghostarchive.org/varchive/youtube/20211031/foRUrxkx2MU| archive-date=2021-10-31 | url-status=live|title=First hydroponics experiment video of William Frederick Gericke in 1930s|date=June 25, 2021|website=[[YouTube]]}}{{cbignore}}</ref> He also wanted to make sure all aspects of hydroponic cultivation were researched and tested before making any of the specifics available to the public.<ref>{{Cite news|url= https://gardenculturemagazine.com/history-of-hydroponics-part-iii-applying-the-science/|title= History of hydroponics|work= Garden Culture Magazine|access-date= Aug 18, 2022|language= en-US}}</ref> Reports of Gericke's work and his claims that hydroponics would revolutionize plant agriculture prompted a huge number of requests for further information. Gericke had been denied use of the university's [[greenhouse]]s for his experiments due to the administration's skepticism, and when the university tried to compel him to release his preliminary nutrient recipes developed at home, he requested greenhouse space and time to improve them using appropriate research facilities. While he was eventually provided greenhouse space, the university assigned [[Dennis Robert Hoagland|Hoagland]] and [[Daniel I. Arnon|Arnon]] to re-evaluate Gericke's claims and show his formula held no benefit over soil grown plant yields, a view held by Hoagland. Because of these irreconcilable conflicts, Gericke left his academic position in 1937 in a climate that was politically unfavorable and continued his research independently in his greenhouse. In 1940, Gericke, whose work is considered to be the basis for all forms of hydroponic growing, published the book, ''Complete Guide to Soilless Gardening''. Therein, for the first time, he published his basic formulas involving the macro- and micronutrient salts for hydroponically grown plants.<ref name=Gericke />

As a result of research of Gericke's claims by order of the Director of the ''California Agricultural Experiment Station'' of the [[University of California, Berkeley|University of California]], [[Claude B. Hutchison|Claude Hutchison]], Dennis Hoagland and [[Daniel Arnon]] wrote a classic 1938 agricultural bulletin, ''The Water Culture Method for Growing Plants Without Soil'', one of the most important works on solution culture ever, which made the claim that hydroponic [[crop yield]]s were no better than crop yields obtained with good-quality soils.<ref>{{Cite book|hdl=2027/uc2.ark:/13960/t51g1sb8j |title=The water-culture method for growing plants without soil|last1=Hoagland|first1=D. R|last2=Arnon|first2=D. I|publisher=University of California, College of Agriculture, Agricultural Experiment Station|year=1938|series=Circular|location=Berkeley, CA |oclc=870260644}}</ref> Ultimately, crop yields would be limited by factors other than mineral nutrients, especially light and aeration of the culture medium.<ref>{{Cite journal|last1=Arnon|first1=D. I.|last2=Hoagland|first2=D. R.|date=1940|title=Crop production in artificial culture solutions and in soils with special reference to factors influencing yields and absorption of inorganic nutrients|journal=Soil Science|volume=50|issue=1|pages=463–485}}</ref> However, in the introduction to his landmark book on soilless cultivation, published two years later, Gericke pointed out that the results published by Hoagland and Arnon in comparing the yields of experimental plants in sand, soil and solution cultures, were based on several [[Observational error|systemic errors]] (''"...these experimenters have made the mistake of limiting the productive capacity of hydroponics to that of soil. Comparison can be only by growing as great a number of plants in each case as the fertility of the culture medium can support."'').<ref name=Gericke />
[[File:Hydroponic farming, USA (9386).jpg|thumb|A lettuce hydroponic farm in [[Fellsmere, Florida]], USA.]]
For example, the Hoagland and Arnon study did not adequately appreciate that hydroponics has other key benefits compared to soil culture including the fact that the roots of the plant have constant access to [[oxygen]] and that the plants have access to as much or as little water and nutrients as they need.<ref name=Gericke /><ref>{{Cite news|url=https://www.hydroponic-urban-gardening.com/hydroponics-guide/various-hydroponics-systems/?L=1&tx_pwcomments_pi1%5Bcomment%5D=22&cHash=9b7ec89c9c292cc1efca10f6d13f3b45&tx_pwcomments_pi1%5BcommentToReplyTo%5D=22&tx_pwcomments_pi1%5Baction%5D=new&tx_pwcomments_pi1%5Bcontroller%5D=Comment|title=Various hydroponics systems|work=Hydroponic Urban Gardening Blog|access-date=Feb 5, 2020|language=en-US}}</ref> This is important as one of the most common errors when cultivating plants is over- and underwatering; hydroponics prevents this from occurring as large amounts of water, which may drown root systems in soil, can be made available to the plant in hydroponics, and any water not used, is drained away, recirculated, or actively aerated, eliminating [[Anoxic waters|anoxic]] conditions in the root area. In soil, a grower needs to be very experienced to know exactly how much water to feed the plant. Too much and the plant will be unable to access oxygen because [[Soil gas|air]] in the [[Pore space in soil|soil pores]] is displaced, which can lead to [[root rot]]; too little and the plant will undergo [[Moisture stress|water stress]] or lose the ability to [[Active transport|absorb]] nutrients, which are typically moved into the roots while [[Solvation|dissolved]], leading to nutrient deficiency symptoms such as [[chlorosis]] or [[fertilizer burn]]. Eventually, Gericke's advanced ideas led to the implementation of hydroponics into commercial agriculture while Hoagland's views and helpful support by the University prompted [[Dennis Robert Hoagland#Bibliography|Hoagland and his associates]] to develop several new formulas (recipes) for mineral nutrient solutions, universally known as [[Hoagland solution]].<ref>{{cite book |last1=Texier |first1=William |title=Hydroponics For Everybody: All About Home Horticulture |date=2013 |publisher=Mamaéditions.com |isbn=978-2-84594-081-9 |page=235 }}{{self-published inline|date=March 2025}}</ref>

One of the earliest successes of hydroponics occurred on [[Wake Island]], a rocky atoll in the Pacific Ocean used as a refueling stop for [[Pan American Airlines]]. Hydroponics was used there in the 1930s to grow vegetables for the passengers. Hydroponics was a necessity on Wake Island because there was no soil, and it was prohibitively expensive to airlift in fresh vegetables.<ref>{{Cite journal|last=Taylor|first=F. J.|date=Jul 1939|title=Nice Clean Gardening|url=https://books.google.com/books?id=GkEEAAAAMBAJ&pg=PA14|journal=[[The Rotarian]]|volume=55|issue=1|pages=14–15|issn=0035-838X}}</ref>

From 1943 to 1946, [[Daniel I. Arnon]] served as a major in the [[United States Army]] and used his prior expertise with plant nutrition to feed troops stationed on barren [[Ponape Island]] in the western [[Pacific Ocean|Pacific]] by growing crops in gravel and nutrient-rich water because there was no [[arable land]] available.<ref name=NYTObit>{{cite news |last1=Sullivan |first1=Walter |title=Daniel Arnon, 84, Researcher And Expert on Photosynthesis |url=https://www.nytimes.com/1994/12/23/obituaries/daniel-arnon-84-researcher-and-expert-on-photosynthesis.html |work=The New York Times |date=23 December 1994 }}</ref>

In the 1960s, Allen Cooper of England developed the [[nutrient film technique]].<ref>{{Cite book|title=The ABC of NFT: nutrient film technique: the world's first method of crop production without a solid rooting medium|last=Cooper|first=A. J.|date=1979|publisher=Grower Books|isbn=0-901361-22-4|location=London|oclc=5809348}}{{pn|date=March 2025}}</ref> [[The Land (Disney)|The Land Pavilion]] at Walt Disney World's EPCOT Center opened in 1982 and prominently features a variety of hydroponic techniques.

In recent decades, [[NASA]] has done extensive hydroponic research for its [[Controlled Ecological Life Support System]] (CELSS) and Advanced Life Support (ALS) programs. <ref>Wheeler, R.M., C.L. Mackowiak, W.L. Berry, G.W. Stutte, N.C. Yorio, and L.M. Ruffe. 1997. Ten years of hydroponic research in NASA's CELSS biomass production chamber.  Proc. 18th Annual Conf., Hydroponic Society of America, pp. 103-113.: </ref><ref>Wheeler, R.M., C.L. Mackowiak, W.L. Berry, G.W. Stutte, N.C. Yorio, L.M. Ruffe, and J.C. Sager. 1999. Nutrient, acid, and water budgets of hydroponically grown crops. Acta Horticulturae 481:655-661. </ref> Hydroponics research mimicking space environments will need further study for different gravity environments, for example u-gravity in Low Earth Orbit, 1/6 g on the Moon, and 1/3 g on Mars. [[Raymond M. Wheeler|Ray Wheeler]], a plant physiologist at Kennedy Space Center's Space Life Science Lab, believes that hydroponics will allow water and nutrient recycling needed for space travel and eventual bioregenerative life support systems where plants are used to produce oxygen and food, while removing carbon dioxide.<ref>{{cite web|url=https://www.nasa.gov/vision/earth/livingthings/biofarming.html|title=Farming for the Future|last=Heiney|first=A.|date=Aug 27, 2004|website=www.nasa.gov|access-date=Nov 21, 2018|archive-date=August 29, 2023|archive-url=https://web.archive.org/web/20230829074535/https://www.nasa.gov/vision/earth/livingthings/biofarming.html}}</ref><ref>	Wheeler, R.M. 2017. Agriculture for space: People and places paving the way.  Open Agriculture 2017 (2):14-32. </ref>

As of 2017, Canada had hundreds of acres of large-scale commercial hydroponic greenhouses, producing tomatoes, peppers and cucumbers.<ref name="marketplace2017">{{cite web|last1=Schaefer|first1=Karen|title=Canadian greenhouse industry seeks methods to reduce pollution into Lake Erie|url=http://www.marketplace.org/2017/01/02/sustainability/canadian-greenhouse-industry-seeks-methods-reduce-pollution-lake-erie|website=Marketplace.org|access-date=17 January 2017|date=2017-01-02}}</ref>

Due to technological advancements within the industry and numerous [[Factors of production|economic factors]], the global hydroponics market is forecast to grow from US$226.45 million in 2016 to US$724.87 million by 2023.<ref>{{cite web|url=https://www.businesswire.com/news/home/20171206006224/en/|title=Global Hydroponics Market Report 2017-2023: Market is expected to grow from $226.45 million in 2016 to reach $724.87 million by 2023 - Research and Markets|last1=Wood|first1=Laura|date=Dec 6, 2017|website=Business Wire|publisher=Berkshire Hathaway|language=en|access-date=Apr 1, 2018}}</ref>{{Update inline|date=April 2023|reason=It is now 2023, has this prediction come true?}}

==Techniques==
Hydroponic systems typically fall into two [[irrigation]] categories: [[Subirrigation|sub-irrigation]] systems, where nutrient solution is supplied from below and roots absorb moisture upward (e.g., deep water culture, ebb-and-flow), and top-irrigation systems, where nutrient solution is applied from above through drip emitters or sprayers (e.g., nutrient film technique, [[aeroponics]]).<ref name="jourVela">{{Cite journal |last=Velázquez-González |first=R. S. |author2=Garcia-Garcia, A. L. |author3=Ventura-Zapata, E. |author4=Barceinas-Sánchez, J. D. O. |author5=Sosa-Savedra, J. C. |year=2022 |title=A Review on Hydroponics and the Technologies Associated for Medium- and Small-Scale Operations |journal=Agriculture |language=en |volume=12 |issue=5 |pages=646 |doi=10.3390/agriculture12050646 |bibcode=2022Agric..12..646V |doi-access=free }}</ref>Hydroponic techniques aim to simultaneously optimize the water, nutrient and oxygen supply to the plant roots. For all techniques, most hydroponic reservoirs are now built of plastic, but other materials have been used, including concrete, glass, metal, vegetable solids, and wood. The containers should exclude light to prevent algae and fungal growth in the hydroponic medium.<ref name="jourVela" />

===Static solution culture===
[[File:CDC South Aquaponics Raft Tank 1 2010-07-17.jpg|thumb|The deep water raft tank at the Crop Diversification Centre (CDC) South [[Aquaponics]] greenhouse in [[Brooks, Alberta]]]]
In static solution culture, plants are grown in containers of nutrient solution, such as glass [[Mason jar]]s (typically, in-home applications), [[Flowerpot|pots]], buckets, tubs, or tanks. The solution is usually gently aerated but may be un-aerated.<ref name=":-3" /> If un-aerated, the solution level is kept low enough that enough roots are above the solution so they get adequate oxygen. A hole is cut (or drilled) in the top of the reservoir for each plant; if it is a jar or tub, it may be its lid, but otherwise, cardboard, foil, paper, wood or metal may be put on top. A single reservoir can be dedicated to a single plant, or to various plants. Reservoir size can be increased as plant size increases. A home-made system can be constructed from food containers or glass canning jars with [[aeration]] provided by an aquarium pump, aquarium airline tubing, aquarium valves or even a [[biofilm]] of [[green algae]] on the glass, through [[photosynthesis]]. Clear containers can also be covered with aluminium foil, butcher paper, black plastic, or other material to eliminate the effects of negative [[phototropism]]. The nutrient solution is changed either on a schedule, such as once per week, or when the concentration drops below a certain level as determined with an [[EC meter|electrical conductivity meter]]. Whenever the solution is depleted below a certain level, either water or fresh nutrient solution is added. A [[Mariotte's bottle]], or a float valve, can be used to automatically maintain the solution level. In raft solution culture, plants are placed in a sheet of buoyant plastic that is floated on the surface of the nutrient solution. That way, the solution level never drops below the roots.<ref name="Suryawanshi Hydroponic Cultivation"/>

===Continuous-flow solution culture===
[[File:Leafy Greens Hydroponics.jpg|thumb|The ''nutrient film technique'' (NFT) being used to grow various salad greens]]
In continuous-flow solution culture, the nutrient solution constantly flows past the roots. It is much easier to automate than the static solution culture because sampling and adjustments to the temperature, pH, and nutrient concentrations can be made in a large storage tank that has potential to serve thousands of plants. A popular variation is the [[nutrient film technique]] or NFT, whereby a very shallow stream of water containing all the dissolved nutrients required for plant growth is recirculated in a thin layer past a bare root mat of plants in a watertight channel, with an upper surface exposed to air. As a consequence, an abundant supply of oxygen is provided to the roots of the plants. A properly designed NFT system is based on using the right channel slope, the right flow rate, and the right channel length. The main advantage of the NFT system over other forms of hydroponics is that the plant roots are exposed to adequate supplies of water, oxygen, and nutrients. In all other forms of production, there is a conflict between the supply of these requirements, since excessive or deficient amounts of one results in an imbalance of one or both of the others. NFT, because of its design, provides a system where all three requirements for healthy plant growth can be met at the same time, provided that the simple concept of NFT is always remembered and practised. The result of these advantages is that higher yields of high-quality produce are obtained over an extended period of cropping. A downside of NFT is that it has very little buffering against interruptions in the flow (e.g., power outages). But, overall, it is probably one of the more productive techniques.<ref>{{cite book |doi=10.1016/B978-0-444-63696-6.00013-X |chapter=Technical Equipment in Soilless Production Systems |title=Soilless Culture |date=2019 |last1=Van Os |first1=E.A. |last2=Gieling |first2=Th. H. |last3=Lieth |first3=J. Heinrich |pages=587–635 |isbn=978-0-444-63696-6 }}</ref>

The same design characteristics apply to all conventional NFT systems. While slopes along channels of 1:100 have been recommended, in practice it is difficult to build a base for channels that is sufficiently true to enable nutrient films to flow without ponding in locally depressed areas. As a consequence, it is recommended that slopes of 1:30 to 1:40 are used.<ref>{{cite web|url=http://www.flairform.com/hints/nft.htm|title=Nutrient Film Technique|website=www.flairform.com|archive-url=https://web.archive.org/web/20180416110457/http://flairform.com/hints/nft.htm|archive-date=2018-04-16|access-date=Nov 22, 2018}}</ref> This allows for minor irregularities in the surface, but, even with these slopes, ponding and [[waterlogging (agriculture)|water logging]] may occur. The slope may be provided by the floor, benches or racks may hold the channels and provide the required slope. Both methods are used and depend on local requirements, often determined by the site and crop requirements.

For nutrient film technique (NFT) systems, recommended flow rates are commonly around 1 L/min per gully to provide sufficient nutrient replenishment to the root film.<ref>{{Cite journal |last=Puerta |first=A. R. |author2=Gabriel, J. |author3=Muro, J. |year=2007 |title=A Modified Nutrient Film Technique System Offers a More Uniform Nutrient Supply to Plants |url=https://journals.ashs.org/view/journals/horttech/17/2/article-p227.xml |journal=HortTechnology |language=en |volume=17 |issue=2 |pages=227–232 |doi=10.21273/HORTTECH.17.2.227}}</ref><ref>{{Cite journal|date=Oct 2014|title=What are the fundamentals of setting up an NFT system?|url=http://www.hydroponics.com.au:80/what-are-the-fundamentals-of-setting-up-an-nft-system|journal=Practical Hydroponics & Greenhouses|publisher=Casper Publications|issue=148|archive-url=https://web.archive.org/web/20170904200942/http://www.hydroponics.com.au/what-are-the-fundamentals-of-setting-up-an-nft-system|archive-date=2017-09-04|via=[[Wayback Machine]]|access-date=2017-05-16}}</ref> At planting, rates may be half this and the upper limit of 2 L/min appears about the maximum. Flow rates beyond these extremes are often associated with nutritional problems. Depressed growth rates of many crops have been observed when channels exceed 12 meters in length. On rapidly growing crops, tests have indicated that, while oxygen levels remain adequate, nitrogen may be depleted over the length of the gully. As a consequence, channel length should not exceed 10–15 meters. In situations where this is not possible, the reductions in growth can be eliminated by placing another nutrient feed halfway along the gully and halving the flow rates through each outlet.<ref>{{Cite web |title=Dissolved Oxygen and Water {{!}} U.S. Geological Survey |url=https://www.usgs.gov/special-topics/water-science-school/science/dissolved-oxygen-and-water |access-date=2022-10-19 |website=www.usgs.gov|date=22 October 2019 }}</ref><ref name="Suryawanshi Hydroponic Cultivation"/>

===Aeroponics===
{{Main|Aeroponics}}
[[Aeroponics]] is a system wherein roots are continuously or discontinuously kept in an environment saturated with fine drops (a [[mist]] or [[aerosol]]) of nutrient solution. The method requires no substrate and entails growing plants with their roots suspended in a deep air or growth chamber with the roots periodically wetted with a fine mist of [[Atomizer nozzle|atomized nutrients]]. Excellent aeration is the main advantage of aeroponics.
[[File:Systeme AEROPONIC.svg|thumb|upright=1.5|A diagram of the [[Aeroponics|aeroponic technique]]]]
Aeroponic techniques have proven to be commercially successful for propagation, seed germination, seed potato production, tomato production, leaf crops, and micro-greens.<ref>{{Cite journal|date=2008|title=Commercial Aeroponics: The Grow Anywhere Story|url=https://sivb.org/InVitroReport/42-2/research.htm|journal=In Vitro Report|volume=44|series=Research News|publisher=The Society for In Vitro Biology|issue=2|access-date=2018-11-22|archive-url=https://web.archive.org/web/20170131001154/https://sivb.org/InVitroReport/42-2/research.htm|archive-date=2017-01-31}}</ref> Since inventor Richard Stoner commercialized aeroponic technology in 1983, aeroponics has been implemented as an alternative to water intensive hydroponic systems worldwide.<ref>{{Cite journal|last=Stoner|first=R. J.|date=Sep 22, 1983|title=Aeroponics Versus Bed and Hydroponic Propagation|url=https://www.biocontrols.com/aero28.html|journal=Florists' Review|volume=173|issue=4477|via=AgriHouse}}</ref> A major limitation of hydroponics is the fact that {{convert|1|kg}} of water can only hold {{convert|8|mg}} of air, no matter whether aerators are utilized or not.

Another distinct advantage of aeroponics over hydroponics is that any species of plants can be grown in a true aeroponic system because the microenvironment of an aeroponic can be finely controlled. Another limitation of hydroponics is that certain species of plants can only survive for so long in water before they become [[waterlogging (agriculture)|waterlogged]]. In contrast, suspended aeroponic plants receive 100% of the available oxygen and carbon dioxide to their roots zone, stems, and leaves,<ref>{{Cite journal|last=Stoner|first=R. J.|date=1983|title=Rooting in Air|journal=Greenhouse Grower|volume=1|issue=11}}</ref><ref>{{Cite web |title=Aeroponic System: A Comprehensive Guide for Agriculture Enthusiasts |url=https://www.agriculturelandusa.com/2024/03/Aeroponic-system.html |access-date=2024-05-21 |website=Agriculture land usa |language=en-US}}</ref> thus accelerating biomass growth and reducing rooting times. [[NASA]] research has shown that aeroponically grown plants have an 80% increase in dry weight biomass (essential minerals) compared to hydroponically grown plants. Aeroponics also uses 65% less water than hydroponics. NASA concluded that aeroponically grown plants require ¼ the nutrient input compared to hydroponics.<ref name=":1">{{cite journal |title=Progressive Plant Growing Has Business Blooming |journal=Spinoff 2006 |date=September 2006 |url=https://ntrs.nasa.gov/citations/20070019327 }}</ref><ref>{{cite journal |last1=Ritter |first1=E. |last2=Angulo |first2=B. |last3=Riga |first3=P. |last4=Herrán |first4=C. |last5=Relloso |first5=J. |last6=San Jose |first6=M. |title=Comparison of hydroponic and aeroponic cultivation systems for the production of potato minitubers |journal=Potato Research |date=June 2001 |volume=44 |issue=2 |pages=127–135 |doi=10.1007/bf02410099 }}</ref> Unlike hydroponically grown plants, aeroponically grown plants will not suffer transplant shock when transplanted to soil, and offers growers the ability to reduce the spread of disease and pathogens.{{fact|date=March 2025}}

Aeroponics is also widely used in laboratory studies of plant physiology and plant pathology. Aeroponic techniques have been given special attention from NASA since a mist is easier to handle than a liquid in a zero-gravity environment.<ref name=":1" /><ref name="Suryawanshi Hydroponic Cultivation"/>

===Fogponics===
{{Main|Fogponics}}
Fogponics is a derivation of aeroponics wherein the nutrient solution is aerosolized by a [[ultrasonic humidifier|diaphragm vibrating at ultrasonic frequencies]]. Solution droplets produced by this method tend to be 5–10&nbsp;μm in diameter, smaller than those produced by forcing a nutrient solution through pressurized nozzles, as in aeroponics. The smaller size of the droplets allows them to diffuse through the air more easily, and deliver nutrients to the roots without limiting their access to oxygen.<ref>{{Cite news|url=https://www.maximumyield.com/figuring-out-fogponics/2/1361|title=Figuring Out Fogponics|last=Elliott|first=S.|date=Dec 27, 2016|work=Maximum Yield|access-date=Mar 15, 2017|language=en|archive-date=June 1, 2023|archive-url=https://web.archive.org/web/20230601050951/https://www.maximumyield.com/figuring-out-fogponics/2/1361}}</ref><ref>{{cite journal |last1=Rakib Uddin |first1=M |last2=Suliaman |first2=M F |title=Energy efficient smart indoor fogponics farming system |journal=IOP Conference Series: Earth and Environmental Science |date=February 2021 |volume=673 |issue=1 |article-number=012012 |doi=10.1088/1755-1315/673/1/012012 |bibcode=2021E&ES..673a2012R |doi-access=free }}</ref>

===Passive sub-irrigation===
{{Main|Passive hydroponics}}
[[File:Water-cultivate a crocus.jpg|thumb|upright|[[Water plant]]-cultivated [[crocus]]]]
Passive sub-irrigation, also known as passive hydroponics, semi-hydroponics, or ''hydroculture'',<ref>{{Cite news|url=https://www.agriculturelandusa.com/2024/02/Hydroponic-farming.html|title=Hydroponic Farming: How to Grow Plants Without Soil|work=Agriculture land usa|access-date=Feb 13, 2024|language=en-GB}}</ref> is a method wherein plants are grown in an [[Chemically inert|inert]] [[porous]] medium that moves water and fertilizer to the roots by [[capillary action]] from a separate reservoir as necessary, reducing labor and providing a constant supply of water to the roots. In the simplest method, the pot sits in a shallow solution of fertilizer and water or on a capillary mat saturated with nutrient solution. The various hydroponic media available, such as [[ex-clay|expanded clay]] and [[Coir|coconut husk]], contain more air space than more traditional potting mixes, delivering increased oxygen to the roots, which is important in [[epiphyte|epiphytic]] plants such as [[Orchidaceae|orchids]] and [[Bromeliaceae|bromeliads]], whose roots are exposed to the air in nature. Additional advantages of passive hydroponics are the reduction of root rot.{{fact|date=March 2025}}

===Ebb and flow (flood and drain) sub-irrigation===
[[File:Systeme FLOOD&DRAIN 573px.jpg|thumb|An ''ebb and flow'', or ''flood and drain'', hydroponics system]]
{{Main|Ebb and flow hydroponics}}
In its simplest form, nutrient-enriched water is pumped into containers with plants in a growing medium such as [[Expanded clay aggregate]]  At regular intervals, a simple timer causes a pump to fill the containers with nutrient solution, after which the solution drains back down into the reservoir. This keeps the medium regularly flushed with nutrients and air.<ref>{{cite web |url=http://www.makehydroponics.com/whatsystem/flood-and-drain.htm |title=Flood and Drain or Ebb and Flow |publisher=www.makehydroponics.com |access-date=2013-05-17 |archive-url=https://web.archive.org/web/20130217071200/http://www.makehydroponics.com/whatsystem/flood-and-drain.htm |archive-date=2013-02-17  }}</ref>

===Run-to-waste===
In a run-to-waste system, nutrient and water solution is periodically applied to the medium surface. The method was invented in [[Bengal]] in 1946; for this reason it is sometimes referred to as "The Bengal System".{{sfn|Douglas|1975|p=10}}

[[File:Bengal System.png|thumb|A ''run-to-waste'' hydroponics system, referred to as "The [[Bengal]] System" after the region in eastern India where it was invented (circa 1946)]]

This method can be set up in various configurations. In its simplest form, a nutrient-and-water solution is manually applied one or more times per day to a container of inert growing media, such as rockwool, perlite, vermiculite, coco fibre, or sand. In a slightly more complex system, it is automated with a delivery pump, a timer and irrigation tubing to deliver nutrient solution with a delivery frequency that is governed by the key parameters of plant size, plant growing stage, climate, substrate, and substrate conductivity, pH, and water content.{{fact|date=March 2025}}

In a commercial setting, watering frequency is multi-factorial and governed by computers or [[Programmable logic controller|PLCs]].

Commercial hydroponics production of large plants like tomatoes, cucumber, and peppers uses one form or another of run-to-waste hydroponics.

===Deep water culture===
[[File:Hungarian wax peppers roots being revealed IMG 5673.JPG|thumb|upright|The ''deep water culture'' technique being used to grow [[Hungarian wax pepper]]s]]
{{Main|Deep water culture}}
The hydroponic method of plant production by means of suspending the plant roots in a solution of nutrient-rich, oxygenated water. Traditional methods favor the use of plastic buckets and large containers with the plant contained in a net pot suspended from the centre of the lid and the roots suspended in the nutrient solution.
The solution is oxygen saturated by an air pump combined with [[airstone|porous stones]]. With this method, the plants grow much faster because of the high amount of oxygen that the roots receive.<ref name="Growell">{{cite web|url=http://www.growell.co.uk/pr/60/Deep-Water-Culture-It-s-all-about-the-bubbles-.html|title=Deep Water Culture|website=GroWell Hydroponics & Plant Lighting|archive-url=https://web.archive.org/web/20100413041448/http://www.growell.co.uk/pr/60/Deep-Water-Culture-It-s-all-about-the-bubbles-.html|archive-date=April 13, 2010}}</ref> The [[Kratky Method]] is similar to deep water culture, but uses a non-circulating water reservoir.

====Top-fed deep water culture====
''Top-fed'' deep water culture is a technique involving delivering highly oxygenated nutrient solution direct to the root zone of plants. While deep water culture involves the plant roots hanging down into a reservoir of nutrient solution, in top-fed deep water culture the solution is pumped from the reservoir up to the roots (top feeding). The water is released over the plant's roots and then runs back into the reservoir below in a constantly recirculating system. As with deep water culture, there is an [[airstone]] in the reservoir that pumps air into the water via a hose from outside the reservoir. The airstone helps add oxygen to the water. Both the airstone and the water pump run 24 hours a day.{{fact|date=March 2025}}

The biggest advantage of top-fed deep water culture over standard deep water culture is increased growth during the first few weeks.{{citation needed|reason=An important claim likes this needs a good reference.|date=April 2016}} With deep water culture, there is a time when the roots have not reached the water yet. With top-fed deep water culture, the roots get easy access to water from the beginning and will grow to the reservoir below much more quickly than with a deep water culture system. Once the roots have reached the reservoir below, there is not a huge advantage with top-fed deep water culture over standard deep water culture. However, due to the quicker growth in the beginning, grow time can be reduced by a few weeks.{{Citation needed|date=January 2017}}

== Advantages ==
* '''Space optimization''': [[Vertical farming]] and advanced control technologies maximize the use of limited spaces.  
* '''Resource management''': Reduced water and fertilizer consumption through the recycling of nutrient solutions.  
* '''Protection for sensitive species''': Controlled conditions shield plants from climatic extremes, pests, and diseases.

Hydrozones lie at the intersection of urban agriculture innovations, environmental concerns, and biodiversity conservation efforts. Notable examples include specialized botanical gardens, cultivation facilities for threatened endemic species, and domestic spaces for advanced horticulture enthusiasts.

===Rotary===
[[File:Expo 2015 - Coltura idroponica al padiglione del Belgio.jpg|thumb|upright|A rotary hydroponic cultivation demonstration at the Belgian Pavilion Expo in 2015]]
A rotary hydroponic garden is a style of commercial hydroponics created within a circular frame which rotates continuously during the entire growth cycle of whatever plant is being grown.{{fact|date=March 2025}}

While system specifics vary, systems typically rotate once per hour, giving a plant 24 full turns within the circle each 24-hour period. Within the center of each rotary hydroponic garden can be a high intensity grow light, designed to simulate sunlight, often with the assistance of a mechanized timer.{{fact|date=March 2025}}

Each day, as the plants rotate, they are periodically watered with a hydroponic growth solution to provide all nutrients necessary for robust growth. Due to the plants continuous fight against gravity, plants typically mature much more quickly than when grown in soil or other traditional hydroponic growing systems.<ref>{{cite journal|author=Al-Kodmany, K. |title=The vertical farm: a review of developments and implications for the vertical city |journal=Buildings |volume=8 |issue=2 |pages=1–24|doi=10.3390/buildings8020024|year=2018|doi-access=free}}</ref> Because rotary hydroponic systems have a small size, they allow for more plant material to be grown per area of floor space than other traditional hydroponic systems.<ref>{{cite web|url=https://mvonederland.nl/sites/default/files/media/MVO_factsheet_Skygreens.pdf|title=Commercial Vertical Farming Initiatives|last=Sky Green|date=Jun 17, 2016|website=MVO Netherland|access-date=Nov 22, 2018|author-mask=Sky Green|archive-url=https://web.archive.org/web/20180509013713/https://mvonederland.nl/sites/default/files/media/MVO_factsheet_Skygreens.pdf|archive-date=May 9, 2018}}</ref>

Rotary hydroponic systems should be avoided in most circumstances, mainly because of their experimental nature and their high costs for finding, buying, operating, and maintaining them.<ref>{{cite journal |last1=Manos |first1=Dimitrios-Panagiotis |last2=Xydis |first2=George |title=Hydroponics: are we moving towards that direction only because of the environment? A discussion on forecasting and a systems review |journal=Environmental Science and Pollution Research |date=May 2019 |volume=26 |issue=13 |pages=12662–12672 |doi=10.1007/s11356-019-04933-5 |pmid=30915697 |doi-access=free |bibcode=2019ESPR...2612662M }}</ref>

=== Vertical farming ===
Some benefits of [[vertical farming]] include that plants grown with this technique can take place inside, be stacked up in layers, and can take advantage of soilless plant-growing techniques such as hydroponics.<ref>{{Cite web |title=Vertical Farming – No Longer A Futuristic Concept: USDA ARS |url=https://www.ars.usda.gov/oc/utm/vertical-farming-no-longer-a-futuristic-concept/#:~:text=JA:%20Traditional%20farming%20involves%20planting,other%20methods%20of%20soilless%20agriculture. |access-date=2025-02-24 |website=www.ars.usda.gov}}</ref>

=== Environmental benefits ===
Hydroponic farming offers several environmental benefits when compared to traditional agriculture. The most significant of these is reduced [[Water footprint|water consumption]] and controlled nutrient usage. Hydroponic systems can use up to 90% less water when compared to conventional farming. Also, in hydroponic systems, water and nutrients are recirculated in a controlled environment, eliminating [[Runoff (hydrology)|runoff]] and the discharge of [[Pollutant|pollutants]] into local waterways.<ref name=":8">{{cite journal |title=Closed soilless growing systems: A sustainable solution for Dutch greenhouse horticulture |journal=Water Science and Technology |date=1999 |volume=39 |issue=5 |doi=10.1016/S0273-1223(99)00091-8 }}</ref>

By using hydroponics to grow crops indoors or in greenhouses, land use is minimized, reserving arable soil and land for other purposes. Also, utilizing the controlled environment created for hydroponic farming reduces the need for [[Pesticide|pesticides]] and other chemicals. This is due to the fact that many pests and diseases in farming are soil-borne. Since hydroponics uses other substrates, eliminating soil use, these farming obstacles are reduced.<ref>{{cite journal |last1=Gruda |first1=Nazim |title=Do soilless culture systems have an influence on product quality of vegetables? |journal=Journal of Applied Botany and Food Quality |date=6 May 2009 |volume=82 |pages=141–147 |doi=10.18452/9433 }}</ref>

Using hydroponics systems that grow vertically in a space-efficient manner also makes cultivating crops in urban areas possible. However, These systems can use large amounts of energy due to the use of water filtration systems and [[Lighting|artificial lighting]]. Due to this, the carbon footprint of a hydroponic farm can vary depending on factors like the energy source, local climate, and the scale of the operation. Using renewable energy sources such as solar panels has the possibility of making hydroponic farms more sustainable.<ref name=":8" />

=== Resource use ===
Hydroponic systems use less water than traditional farming due to the system's ability to recirculate water rather than absorb it from the soil or lose it to evaporation.{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} Nutrients are also efficiently delivered to plant roots, minimizing nutrient waste and lowering the cost of fertilizing crops.

=== Higher yields and faster growth ===
Because plants are provided with water, nutrients, and light in a controlled environment, hydroponics allows crops to grow faster and potentially yield more within the same or smaller footprint. Some studies show increases of up to 20–30% in crop yield when compared to traditional farming methods.<ref name=":9" />

=== Year-round production ===
Because hydroponic crops can be grown indoors in controlled environments, crops are not dependent on growing seasons or climate. Additionally, extreme weather conditions such as drought and freezing temperatures are less impactful to crops. This stabilizes production and allows hydroponics to produce crops more consistently year-round than traditional farming.<ref name=":7" />

=== Pest and disease control ===
Since hydroponics uses substrates instead of soil as the base for root growth, soil-borne diseases and pests are eliminated. This reduces the use of chemical pesticides and lowers crop maintenance costs.{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}}

=== Urban crop growth ===
Hydroponic gardens can be set up in urban areas with little to no arable land. They can be constructed on rooftops, in warehouses, or other available space. This provides the opportunity for urban neighborhoods to have crops grown closer to them, allowing for closer delivery and fresher produce for consumers.<ref>{{Cite web |title=Growing {{!}} Controlled Environment Agriculture |url=https://cea.cals.cornell.edu/crops/ |access-date=2025-03-04 |website=cea.cals.cornell.edu}}</ref>

==Substrates (growing support materials)==
Different media are appropriate for different growing techniques.

===Rock wool===
[[File:Rockwool 4lbs per ft3 fibrex5.jpg|thumb|upright|Rock wool]]
Rock wool ([[mineral wool]]) is the most widely used medium in hydroponics. Rock wool is an inert substrate suitable for both run-to-waste and recirculating systems. Rock wool is made from molten rock, basalt or 'slag' that is spun into bundles of single filament fibres, and bonded into a medium capable of capillary action, and is, in effect, protected from most common microbiological degradation. Rock wool is typically used only for the seedling stage, or with newly cut clones, but can remain with the plant base for its lifetime. Rock wool has many advantages and some disadvantages. The latter being the possible skin irritancy (mechanical) whilst handling (1:1000).{{Citation needed|date=April 2016}} Flushing with cold water usually brings relief. Advantages include its proven efficiency and effectiveness as a commercial hydroponic substrate. Most of the rock wool sold to date is a non-hazardous, non-carcinogenic material, falling under Note Q of the European Union Classification Packaging and Labeling Regulation (CLP).{{Citation needed|reason=reliable source|date=October 2012}}

Mineral wool products can be engineered to hold large quantities of water and air that aid root growth and nutrient uptake in hydroponics; their fibrous nature also provides a good mechanical structure to hold the plant stable. The naturally high [[pH]] of mineral wool makes them initially unsuitable to plant growth and requires "conditioning" to produce a wool with an appropriate, stable pH.<ref name="Alexander 1994">{{cite book |title=The Best of Growing Edge |date=1994 |publisher=New Moon Publishing, Inc. |isbn=978-0-944557-01-3 }}{{pn|date=March 2025}}</ref>

===Expanded clay aggregate===
{{Main|Expanded clay aggregate}}
[[File:Hydroton.jpg|upright|thumb|[[Expanded clay aggregate]]]]
Baked clay pellets are suitable for hydroponic systems in which all nutrients are carefully controlled in water solution. The clay pellets are inert, [[pH]]-neutral, and do not contain any nutrient value.

The clay is formed into round pellets and fired in rotary [[kiln]]s at {{convert|1200|C}}. This causes the clay to expand, like popcorn, and become porous. It is light in weight, and does not compact over time. The shape of an individual pellet can be irregular or uniform depending on brand and manufacturing process. The manufacturers consider expanded clay to be an ecologically sustainable and re-usable growing medium because of its ability to be cleaned and sterilized, typically by washing in solutions of white vinegar, [[chlorine]] [[bleach]], or [[hydrogen peroxide]] ({{chem|H|2|O|2}}), and rinsing completely.{{fact|date=March 2025}}

Another view is that clay pebbles are best not re-used even when they are cleaned, due to root growth that may enter the medium. Breaking open a clay pebble after use can reveal this growth.{{Citation needed|date=April 2023}}

===Growstones===
[[Growstones]], made from glass waste, have both more air and water retention space than perlite and peat. This aggregate holds more water than [[parboiled rice hulls]].<ref name=":2">{{cite press release |title=Growstones ideal alternative to perlite, parboiled rice hulls |url=https://www.sciencedaily.com/releases/2011/12/111214144753.htm |work=ScienceDaily |publisher=American Society for Horticultural Science |date=14 December 2011 }}</ref> Growstones by volume consist of 0.5 to 5% [[calcium carbonate]]<ref name=":3">{{cite web|url=http://sunlightsupply.s3.amazonaws.com/documents/product/714230_MSDS.pdf|title=GrowStone Products MSDS|date=Dec 22, 2011|publisher=Growstone, LLC|access-date=Nov 22, 2018|archive-url=https://web.archive.org/web/20180410062314/http://sunlightsupply.s3.amazonaws.com/documents/product/714230_MSDS.pdf|archive-date=April 10, 2018}}</ref> – for a standard 5.1&nbsp;kg bag of Growstones that corresponds to 25.8 to 258 grams of [[calcium carbonate]]. The remainder is soda-lime glass.<ref name=":3" />

===Coconut coir===
[[File:Mother plants in flower.jpg|thumb|"Mother" cannabis plants growing in coir with added perlite.]]
[[Coconut coir]], also known as coir peat, is a natural byproduct derived from coconut processing. The outer husk of a coconut consists of fibers which are commonly used to make a myriad of items ranging from floor mats to brushes.  After the long fibers are used for those applications, the dust and short fibers are merged to create coir. Coconuts absorb high levels of nutrients throughout their life cycle, so the coir must undergo a maturation process before it becomes a viable growth medium.<ref>{{cite journal |last1=Namasivayam |first1=C. |last2=Sangeetha |first2=D. |title=Application of coconut coir pith for the removal of sulfate and other anions from water |journal=Desalination |date=January 2008 |volume=219 |issue=1–3 |pages=1–13 |doi=10.1016/j.desal.2007.03.008 |bibcode=2008Desal.219....1N }}</ref> This process removes salt, tannins and phenolic compounds through substantial water washing. Contaminated water is a byproduct of this process, as three hundred to six hundred liters of water per one cubic meter of coir are needed.<ref>[Pavlis, Robert. "Is Coir an Eco-Friendly Substitute for Peat Moss?" Garden Myths, 22 July 2017, http://www.gardenmyths.com/coir-ecofriendly-substitute-peat-moss/.].</ref> Additionally, this maturation can take up to six months and one study concluded the working conditions during the maturation process are dangerous and would be illegal in North America and Europe.<ref>{{cite journal |last1=Panicker |first1=Venugopal |last2=Karunakaran |first2=Raseela |last3=Ravindran |first3=C. |title=Nasobronchial allergy and pulmonary function abnormalities among coir workers of Alappuzha |journal=The Journal of the Association of Physicians of India |date=July 2010 |volume=58 |pages=420–422 |pmid=21121206 }}</ref> Despite requiring attention, posing health risks and environmental impacts, coconut coir has impressive material properties. When exposed to water, the brown, dry, chunky and fibrous material expands nearly three or four times its original size. This characteristic combined with coconut coir's water retention capacity and resistance to pests and diseases make it an effective growth medium. Used as an alternative to rock wool, coconut coir offers optimized growing conditions.<ref>{{cite journal |last1=Barrett |first1=G.E. |last2=Alexander |first2=P.D. |last3=Robinson |first3=J.S. |last4=Bragg |first4=N.C. |title=Achieving environmentally sustainable growing media for soilless plant cultivation systems – A review |journal=Scientia Horticulturae |date=November 2016 |volume=212 |pages=220–234 |doi=10.1016/j.scienta.2016.09.030 |doi-access=free |bibcode=2016ScHor.212..220B }}</ref>

===Rice husks===
[[File:Rice husk.jpg|thumb|upright|Rice husks]]
[[Rice husks#Fertilizer and substrate|Parboiled rice husks]] (PBH) are an agricultural byproduct that would otherwise have little use. They decay over time, and allow drainage,<ref name="woodfibre pgr" /> and even retain less water than growstones.<ref name=":2" /> A study showed that rice husks did not affect the effects of [[plant hormones|plant growth regulators]].<ref name="woodfibre pgr" />{{Primary source inline|reason=See wood fiber.|date=March 2016}}

===Perlite===
[[File:Schultz Horticultural Perlite.jpg|thumb|upright|Perlite]]
[[Perlite]] is a volcanic rock that has been superheated into very lightweight expanded glass pebbles. It is used loose or in plastic sleeves immersed in the water. It is also used in potting soil mixes to decrease soil density. It does contain a high amount of fluorine which could be harmful to some plants.<ref>{{cite web|last=Stallsmith |first=Audrey |url=https://www.bobvila.com/articles/vermiculite-vs-perlite/ |title=Vermiculite vs Perlite: Which is Best for Your Potted Plants? |publisher=Bob Vila |date=2021-11-24 |access-date=2022-08-03}}</ref> Perlite has similar properties and uses to [[vermiculite]] but, in general, holds more air and less water and is buoyant.

===Vermiculite===
[[File:Vermiculite1.jpg|thumb|upright|Vermiculite]]
Like perlite, [[vermiculite]] is a mineral that has been superheated until it has expanded into light pebbles. Vermiculite holds more water than perlite and has a natural "wicking" property that can draw water and nutrients in a passive hydroponic system. If too much water and not enough air surrounds the plants roots, it is possible to gradually lower the medium's water-retention capability by mixing in increasing quantities of perlite.

===Pumice===
[[File:Pumice.JPG|thumb|upright|Pumice stone]]
Like perlite, [[pumice]] is a lightweight, mined volcanic rock that finds application in hydroponics.

===Sand===
Sand is cheap and easily available. However, it is heavy, does not hold water very well, and it must be sterilized between uses.<ref>{{Cite news|url=https://fvsugreenhouse.wordpress.com/2014/06/13/an-intro-into-sand-culture-hydroponics/|title=An Intro Into Sand Culture Hydroponics|date=Jun 13, 2014|work=The FVSU Greenhouse Project|access-date=Nov 22, 2018|language=en-US}}</ref>

===Gravel===
The same type that is used in aquariums, though any small gravel can be used, provided it is washed first. Indeed, plants growing in a typical traditional gravel filter bed, with water circulated using electric powerhead pumps, are in effect being grown using gravel hydroponics, also termed "nutriculture". Gravel is inexpensive, easy to keep clean, drains well and will not become waterlogged. However, it is also heavy, and, if the system does not provide continuous water, the plant roots may dry out.

===Wood fiber===
[[File:Palha de madeira2.jpg|thumb|upright|Excelsior, or wood wool]]
[[Wood fibre]], produced from steam friction of wood, is an efficient organic substrate for hydroponics. It has the advantage that it keeps its structure for a very long time. [[Wood wool]] (i.e. wood slivers) have been used since the earliest days of the hydroponics research.<ref name=Gericke /> However, more recent research suggests that wood fibre may have detrimental effects on "plant growth regulators".<ref name="woodfibre pgr">{{cite web|url=http://www.purdue.edu/newsroom/research/2010/101025LopezHulls.html|title=Rice hulls a sustainable drainage option for greenhouse growers|last=Wallheimer|first=Brian|date=Oct 25, 2010|publisher=Purdue University|access-date=Aug 30, 2012|archive-date=October 18, 2017|archive-url=https://web.archive.org/web/20171018223549/http://www.purdue.edu/newsroom/research/2010/101025LopezHulls.html}}</ref>{{Primary source inline|reason=This citation is vague in its description of its findings and is in contradiction of more established science suggesting that wood fiber is an adequate media choice. This claim needs a better citation for support.|date=March 2016}}

===Sheep wool===
[[Wool]] from shearing [[sheep]] is a little-used yet promising renewable growing medium. In a study comparing wool with peat slabs, coconut fibre slabs, perlite and rockwool slabs to grow cucumber plants, sheep wool had a greater air capacity of 70%, which decreased with use to a comparable 43%, and water capacity that increased from 23% to 44% with use.<ref name=":4">{{cite journal |last1=Böhme |first1=M. |last2=Schevchenko |first2=J. |last3=Pinker |first3=I. |last4=Herfort |first4=S. |title=Cucumber grown in sheepwool slabs treated with biostimulator compared to other organic and mineral substrates |journal=Acta Horticulturae |date=January 2008 |issue=779 |pages=299–306 |doi=10.17660/actahortic.2008.779.36 }}</ref> Using sheep wool resulted in the greatest yield out of the tested substrates, while application of a biostimulator consisting of humic acid, lactic acid and Bacillus subtilis improved yields in all substrates.<ref name=":4" />

===Brick shards===
Brick shards have similar properties to gravel. They have the added disadvantages of possibly altering the pH and requiring extra cleaning before reuse.<ref name="auto">{{cite book |last1=Parker |first1=Rick |title=Plant & Soil Science: Fundamentals & Applications |date=2009 |publisher=Cengage Learning |url=https://books.google.com/books?id=oSkEAAAAQBAJ&pg=PP1 |access-date=22 January 2019|isbn=978-1-111-78077-7 }}</ref>

===Polystyrene packing peanuts===
[[File:Foam Peanuts.jpg|thumb|upright|Polystyrene foam peanuts]]
Polystyrene [[packing peanuts]] are inexpensive, readily available, and have excellent drainage. However, they can be too lightweight for some uses. They are used mainly in closed-tube systems. Note that non-biodegradable [[polystyrene]] peanuts must be used; biodegradable packing peanuts will decompose into a sludge. Plants may absorb [[styrene]] and pass it to their consumers; this is a possible health risk.<ref name="auto"/>

==Nutrient solutions==
===Inorganic hydroponic solutions===
The [[formulation]] of hydroponic solutions is an application of [[plant nutrition]], with nutrient deficiency symptoms mirroring those found in traditional [[Agricultural soil science|soil based agriculture]]. However, the underlying chemistry of hydroponic solutions can differ from [[Soil nutrient|soil chemistry]] in many significant ways. Important differences include:
* Unlike soil, hydroponic nutrient solutions do not have [[cation-exchange capacity]] (CEC) from clay particles or organic matter. The absence of CEC and [[soil pore]]s means the [[pH]], [[oxygen saturation]], and nutrient concentrations can change much more rapidly in hydroponic setups than is possible in soil.
* Selective absorption of nutrients by plants often imbalances the amount of [[counterion]]s in solution.<ref name=Gericke />{{sfn|Douglas|1985|p={{pn|date=March 2025}}}}{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} This imbalance can rapidly affect solution pH and the ability of plants to absorb nutrients of similar ionic charge (see article [[membrane potential]]). For instance, nitrate [[anion]]s are often consumed rapidly by plants to form [[protein]]s, leaving an excess of [[cation]]s in solution.<ref name=Gericke>{{cite book|last1=Gericke|first1=William F.|title=The Complete Guide to Soilless Gardening|date=1940|publisher=Putnam|location=London|isbn=978-1-163-14049-9|pages=[https://archive.org/details/soillessgardenin031829mbp/page/n30 9]–10, 38 & 84|edition=1st|url=https://archive.org/details/soillessgardenin031829mbp}}</ref> This cation imbalance can lead to deficiency symptoms in other cation based nutrients (e.g. [[Magnesium|Mg<sup>2+</sup>]]) even when an ideal quantity of those nutrients are dissolved in the solution.{{sfn|Douglas|1985|p={{pn|date=March 2025}}}}{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}}
* Depending on the pH or on the presence of [[Water pollution|water contaminants]], nutrients such as iron can [[Precipitation (chemistry)|precipitate]] from the solution and become unavailable to plants. Routine adjustments to pH, [[Buffer solution|buffering]] the solution, or the use of [[chelating agent]]s is often necessary.<ref>{{Cite journal|last1= Lea-Cox|first1= J. D.|last2= Stutte|first2= G. W.|last3= Berry|first3= W. L.|last4= Wheeler|first4= R. M.|date= 1996|title= Charge balance - a theoretical basis for modulating pH fluctuations in plant nutrient delivery systems|journal= Life Support & Biosphere Science: International Journal of Earth Space|volume= 3|issue= 1–2|pages= 53–59|pmid= 11539161}}</ref>
* Unlike [[soil type]]s, which can vary greatly in their [[Chemical composition|composition]], hydroponic solutions are often [[Dennis Robert Hoagland#Hewitt's Table 30A|standardized]] and require routine maintenance for plant cultivation.<ref>{{cite journal|title=Optimum nutrient solutions for plants|author=Hoagland, D.R. |journal=Science|year=1920|volume=52|issue=1354|pages=562–564|doi=10.1126/science.52.1354.562|pmid=17811355|bibcode=1920Sci....52..562H|url=https://zenodo.org/record/1532324}}</ref> Under controlled laboratory conditions hydroponic solutions are periodically pH adjusted to near neutral (pH 6.0) and are aerated with oxygen. Also, water levels must be refilled to account for [[transpiration]] losses and nutrient solutions require re-fortification to correct the nutrient imbalances that occur as plants grow and deplete nutrient reserves. Sometimes the regular measurement of [[nitrate]] ions is used as a key parameter to estimate the remaining proportions and concentrations of other essential nutrient ions to restore a balanced solution.<ref>{{cite journal |last1=Rockel |first1=P. |title=Growth and nitrate consumption of sunflowers in the rhizostat, a device for continuous nutrient supply to plants |journal=Journal of Plant Nutrition |date=October 1997 |volume=20 |issue=10 |pages=1431–1447 |doi=10.1080/01904169709365345 |bibcode=1997JPlaN..20.1431R }}</ref>
* Well-known examples of standardized, balanced nutrient solutions are the [[Hoagland solution]], the [[Long Ashton Research Station#Nutrient solution|Long Ashton nutrient solution]], or the [[Dennis Robert Hoagland#Knop's solution|Knop solution]].
* Nowadays, however, [[Dennis Robert Hoagland#Hybrid nutrient solutions|hybrid nutrient solutions]] play a more important role than the above original or modified solutions of [[Dennis Robert Hoagland|Hoagland]], [[Eric John Hewitt|Hewitt]], or [[Wilhelm Knop|Knop]].<ref>{{cite journal|author1=Nagel, K.A. |author2=Lenz, H. |author3=Kastenholz, B. |author4=Gilmer, F. |author5=Averesch, A. |author6=Putz, A. |author7=Heinz, K. |author8=Fischbach, A. |author9=Scharr, H. |author10=Fiorani, F. |author11=Walter, A. |author12=Schurr, U. |title=The platform ''GrowScreen-Agar'' enables identification of phenotypic diversity in root and shoot growth traits of agar grown plants |journal=Plant Methods |volume=16 |issue=89 |pages=1–17|doi=10.1186/s13007-020-00631-3|pmc=7310412|year=2020|pmid=32582364 |bibcode=2020PlMet..16...89N |doi-access=free}}</ref>

As in conventional agriculture, nutrients should be adjusted to satisfy [[Liebig's law of the minimum]] for each specific plant [[Variety (botany)|variety]].{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} Nevertheless, generally acceptable concentrations for nutrient solutions exist, with minimum and maximum concentration ranges for most plants being somewhat similar.<ref>Steiner, A. A. (1984). "The universal nutrient solution". In: Proceedings of the 6th International Congress Soilless Culture, ISOSC, Wageningen, pp. 633-649.</ref> Most nutrient solutions are mixed to have concentrations between 1,000 and 2,500 [[parts per million|ppm]].<ref name=Gericke /> Acceptable concentrations for the individual nutrient ions, which comprise that total ppm figure, are summarized in the following table. For essential nutrients, concentrations below these ranges often lead to nutrient deficiencies while exceeding these ranges can lead to nutrient toxicity. Optimum nutrition concentrations for plant varieties are found [[empirically]] by experience or by [[plant tissue test]]s.{{sfn|Douglas|1985|p={{pn|date=March 2025}}}}

{| class="wikitable"
|-
! Element !! Role !! Ionic form(s) !! Low range (ppm) !! High range (ppm) !! Common Sources !! Comment
|-
| [[Nitrogen]] || [[Plant nutrition|Essential macronutrient]] || [[Nitrate|NO{{su|b=3|p=−}}]] or [[Ammonium|NH{{su|b=4|p=+}}]]|| 100{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} || 1000{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} || [[KNO3|KNO<sub>3</sub>]], [[NH4NO3|NH<sub>4</sub>NO<sub>3</sub>]], [[Ca(NO3)2|Ca(NO<sub>3</sub>)<sub>2</sub>]], [[HNO3|HNO<sub>3</sub>]], [[(NH4)2SO4|(NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>]], and [[(NH4)2HPO4|(NH<sub>4</sub>)<sub>2</sub>HPO<sub>4</sub>]]
|| NH{{su|b=4|p=+}} interferes with Ca<sup>2+</sup> uptake and can be toxic to plants if used as a major nitrogen source. A 3:1 ratio of NO{{su|b=3|p=−}}-N to NH{{su|b=4|p=+}}-N (''wt%'') is sometimes recommended to balance pH during nitrogen absorption.{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} Plants respond differently depending on the form of nitrogen, e.g., ammonium has a positive charge, and thus, the plant expels one proton (H{{su|b=|p=+}}) for every NH{{su|b=4|p=+}} taken up resulting in a reduction in rhizosphere pH. When supplied with NO{{su|b=3|p=−}}, the opposite can occur where the plant releases bicarbonate (HCO{{su|b=3|p=−}}) which increases rhizosphere pH. These changes in pH can influence the availability of other plant nutrients (e.g., Zn, Ca, Mg).<ref>{{Cite journal|last=Mc Near|first=D. H. Jr.|date=2013|title=The Rhizosphere - roots, soil and everything in between|url=https://www.nature.com/scitable/knowledge/library/the-rhizosphere-roots-soil-and-67500617/|journal=Nature Education|volume=4|issue=3|page=1}}</ref>
|-
| [[Potassium]] || Essential macronutrient || K<sup>+</sup> || 100{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} || 400{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} || KNO<sub>3</sub>, [[K2SO4|K<sub>2</sub>SO<sub>4</sub>]], [[KCl]], [[Potassium hydroxide|KOH]], [[K2CO3|K<sub>2</sub>CO<sub>3</sub>]], [[K2HPO4|K<sub>2</sub>HPO<sub>4</sub>]], and [[Potassium silicate|K<sub>2</sub>SiO<sub>3</sub>]] || High concentrations interfere with the function of Fe, Mn, and Zn. Zinc deficiencies often are the most apparent.{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}}
|-
| [[Phosphorus]] || Essential macronutrient || [[Phosphate|PO{{su|b=4|p=3−}}]] || 30{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} || 100{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} || [[K2HPO4|K<sub>2</sub>HPO<sub>4</sub>]], [[KH2PO4|KH<sub>2</sub>PO<sub>4</sub>]], [[NH4H2PO4|NH<sub>4</sub>H<sub>2</sub>PO<sub>4</sub>]], [[H3PO4|H<sub>3</sub>PO<sub>4</sub>]], and [[Ca3po42|Ca(H<sub>2</sub>PO<sub>4</sub>)<sub>2</sub>]] || Excess NO{{su|b=3|p=−}} tends to inhibit PO{{su|b=4|p=3−}} absorption. The ratio of iron to PO{{su|b=4|p=3−}} can affect [[Precipitation (chemistry)|co-precipitation]] reactions.{{sfn|Douglas|1985|p={{pn|date=March 2025}}}}
|-
| [[Calcium]] || Essential macronutrient || Ca<sup>2+</sup> || 200{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} || 500{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} || [[Ca(NO3)2|Ca(NO<sub>3</sub>)<sub>2</sub>]], [[Ca3po42|Ca(H<sub>2</sub>PO<sub>4</sub>)<sub>2</sub>]], [[CaSO4|CaSO<sub>4</sub>]], [[CaCl2|CaCl<sub>2</sub>]] || Excess Ca<sup>2+</sup> inhibits Mg<sup>2+</sup> uptake.{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}}
|-
| [[Magnesium]] || Essential macronutrient || Mg<sup>2+</sup> || 50{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} || 100{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} || [[MgSO4|MgSO<sub>4</sub>]] and [[MgCl2|MgCl<sub>2</sub>]] || Should not exceed Ca<sup>2+</sup> concentration due to competitive uptake.{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}}
|-
| [[Sulfur]] || Essential macronutrient || [[Sulfate|SO{{su|b=4|p=2−}}]] || 50{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} || 1000{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} || MgSO<sub>4</sub>, K<sub>2</sub>SO<sub>4</sub>, CaSO<sub>4</sub>, [[H2SO4|H<sub>2</sub>SO<sub>4</sub>]], (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>, [[ZnSO4|ZnSO<sub>4</sub>]], [[CuSO4|CuSO<sub>4</sub>]], [[FeSO4|FeSO<sub>4</sub>]], and [[MnSO4|MnSO<sub>4</sub>]] || Unlike most nutrients, plants can tolerate a high concentration of the SO{{su|b=4|p=2−}}, selectively absorbing the nutrient as needed.<ref name=Gericke />{{sfn|Douglas|1985|p={{pn|date=March 2025}}}}{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} Undesirable [[counterion]] effects still apply however.
|-
| [[Iron]] || Essential micronutrient || Fe<sup>3+</sup> and Fe<sup>2+</sup> || 2{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} || 5{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} || Fe[[Pentetic acid|DTPA]], Fe[[EDTA]], iron [[Citric acid|citrate]], [[Ferrous tartrate|iron tartrate]], [[FeCl3|FeCl<sub>3</sub>]], [[Ferric EDTA]], and FeSO<sub>4</sub>
 || [[pH]] values above 6.5 greatly decreases iron solubility. [[Chelating agent]]s (e.g. [[Pentetic acid|DTPA]], [[citric acid]], or EDTA) are often added to increase iron solubility over a greater pH range.{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}}
|-
| [[Zinc]] || Essential micronutrient || Zn<sup>2+</sup> || 0.05{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} || 1{{sfn|Douglas|1985|p={{pn|date=March 2025}}}}|| ZnSO<sub>4</sub> || Excess zinc is highly toxic to plants but is essential for plants at low concentrations. The zinc content of commercially available plant-based food ranges from 3 to 10&nbsp;μg/g fresh weight.<ref>{{Cite journal|last1= Waldner|first1= H.|last2= Günther|first2= K.|date= 1996|title= Characterization of low molecular weight zinc species in normal commercial vegetable foodstuffs|journal= Zeitschrift für Lebensmittel-Untersuchung und Forschung|volume= 202|issue= 3|pages= 256–262|doi= 10.1007/BF01263550|pmid=  8721222|doi-access= free}}</ref>
|-
| [[Copper]] || Essential micronutrient || Cu<sup>2+</sup> || 0.01{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} || 1{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} || CuSO<sub>4</sub> || Plant sensitivity to copper is highly variable. 0.1 ppm can be toxic to some plants{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} while a concentration up to 0.5 ppm for many plants is often considered ideal.{{sfn|Douglas|1985|p={{pn|date=March 2025}}}}
|-
| [[Manganese]] || Essential micronutrient|| Mn<sup>2+</sup> || 0.5{{sfn|Douglas|1985|p={{pn|date=March 2025}}}}{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} || 1{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} || [[MnSO4|MnSO<sub>4</sub>]] and [[MnCl2|MnCl<sub>2</sub>]] || Uptake is enhanced by high [[Phosphate|PO{{su|b=4|p=3−}}]] concentrations.{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}}
|-
| [[Boron]] || Essential micronutrient || [[Boric acid#Properties|B(OH){{su|b=4|p=−}}]] || 0.3{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} || 10{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} || [[H3BO3|H<sub>3</sub>BO<sub>3</sub>]], and [[Na2B4O7|Na<sub>2</sub>B<sub>4</sub>O<sub>7</sub>]] || An essential nutrient, however, some plants are highly sensitive to boron (e.g. toxic effects are apparent in [[citrus]] trees at 0.5 ppm).{{sfn|Douglas|1985|p={{pn|date=March 2025}}}}
|-
| [[Molybdenum]] || Essential micronutrient || [[Molybdate#Equilibria in aqueous solution|MoO{{su|b=4|p=−}}]] || 0.001{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} || 0.05{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} || [[Ammonium heptamolybdate|(NH<sub>4</sub>)<sub>6</sub>Mo<sub>7</sub>O<sub>24</sub>]] and [[Na2MoO4|Na<sub>2</sub>MoO<sub>4</sub>]] || A component of the enzyme [[nitrate reductase]] and required by [[rhizobia]] for [[nitrogen fixation]].{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}}
|-
| [[Chlorine]] || Essential micronutrient || Cl<sup>−</sup> || 0.65<ref>{{cite book|url=https://archive.org/details/watercultureme3450hoag|title=The water-culture method for growing plants without soil|author=Hoagland|author2=Arnon|name-list-style=amp|date=1950|publisher=(Circular (California Agricultural Experiment Station), 347. ed.). Berkeley, Calif. : University of California, College of Agriculture, Agricultural Experiment Station. (Revision)|access-date=1 October 2014}}</ref> || 9<ref>{{cite journal |last1=Smith |first1=G. S. |last2=Johnston |first2=C. M. |last3=Cornforth |first3=I. S. |title=Comparison of nutrient solutions for growth of plants in sand culture |journal=New Phytologist |date=August 1983 |volume=94 |issue=4 |pages=537–548 |doi=10.1111/j.1469-8137.1983.tb04863.x |doi-access=free |bibcode=1983NewPh..94..537S }}</ref> || KCl, CaCl<sub>2</sub>, MgCl<sub>2</sub>, and NaCl || Can interfere with NO{{su|b=3|p=−}} uptake in some plants but can be beneficial in some plants (e.g. in asparagus at 5 ppm). Absent in [[conifer]]s, [[fern]]s, and most [[bryophyte]]s.{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} Chloride is one of the [[Soil nutrient|16 elements]] essential for plant growth. Because it is supposedly needed in small quantities for healthy growth of plants (< 50–100 μM in the nutrient media), chloride is classified as a micronutrient.<ref>{{Cite journal|last1= Franco-Navarro|first1= J. D.|last2= Brumos|first2= J.|last3= Rosales|first3= M. A.|last4= Cubero-Font|first4= P.|last5= Talon|first5= M.|last6= Colmenero-Flores|first6= J. M.|date= 2016|title= Chloride regulates leaf cell size and water relations in tobacco plants|journal= Journal of Experimental Botany|volume= 67|issue= 3|pages= 873–891|doi= 10.1093/jxb/erv502|pmid= 26602947|pmc= 4737079|doi-access= free}}</ref>
|-
| [[Aluminum]] || Variable micronutrient || [[Metal ions in aqueous solution#Aluminium and Group 3 metals|Al<sup>3+</sup>]] || 0 || 10{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} || [[Aluminium sulfate|Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>]]|| Essential for some plants (e.g. [[pea]]s, [[maize]], [[sunflower]]s, and [[cereal]]s). Can be toxic to some plants below 10 ppm.{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} Sometimes used to produce [[biological pigment|flower pigments]] (e.g. by [[Hydrangea]]s).
|-
| [[Silicon]] || Variable micronutrient || [[Silicate|SiO{{su|b=3|p=2−}}]] || 0 || 140{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} || [[Potassium silicate|K<sub>2</sub>SiO<sub>3</sub>]], [[Na2SiO3|Na<sub>2</sub>SiO<sub>3</sub>]], and [[Silicic acid|H<sub>2</sub>SiO<sub>3</sub>]] || Present in most plants, abundant in cereal crops, grasses, and tree bark. Evidence that SiO{{su|b=3|p=2−}} improves plant disease resistance exists.{{sfn|Douglas|1985|p={{pn|date=March 2025}}}}
|-
| [[Titanium]] || Variable micronutrient || Ti<sup>3+</sup> || 0 || 5{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} || [[Titanic acid|H<sub>4</sub>TiO<sub>4</sub>]] || Might be essential but trace Ti<sup>3+</sup> is so ubiquitous that its addition is rarely warranted.{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} At 5 ppm favorable growth effects in some crops are notable (e.g. [[pineapple]] and peas).{{sfn|Douglas|1985|p={{pn|date=March 2025}}}}
|-
| [[Cobalt]] || Variable micronutrient || Co<sup>2+</sup> || 0 || 0.1{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} || [[CoSO4|CoSO<sub>4</sub>]] || Required by rhizobia, important for legume [[Root nodule|root nodulation]].{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} Some [[algae]] require cobalt for the synthesis of [[vitamin B12]].<ref>{{cite journal|title=Methylcobalamin – a form of vitamin B12 identified and characterised in Chlorella vulgaris|author=Kumudha, A.|author2=Selvakumar, S.|author3=Dilshad, P.|author4=Vaidyanathan, G.|author5=Thakur, M.S.|author6=Sarada, R.|journal=Food Chemistry|year=2015|volume=170|pages=316–320|pmid=25306351|doi=10.1016/j.foodchem.2014.08.035}}</ref>
|-
| [[Nickel]] || Variable micronutrient || Ni<sup>2+</sup> || 0.057{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} || 1.5{{sfn|Douglas|1985|p={{pn|date=March 2025}}}} || [[Nickel(II) sulfate|NiSO<sub>4</sub>]] and [[NiCO3|NiCO<sub>3</sub>]] || Essential to many plants (e.g. [[legume]]s and some grain crops).{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} Also used in the enzyme [[urease]].
|-
| [[Sodium]] || Non-essential micronutrient || Na<sup>+</sup> || 0 || 31<ref>{{cite book |last1=Hewitt |first1=Eric John |title=Sand and Water Culture Methods Used in the Study of Plant Nutrition |date=1952 |publisher=Commonwealth Agricultural Bureaux |oclc=1068279167 }}{{pn|date=March 2025}}</ref> || [[Na2SiO3|Na<sub>2</sub>SiO<sub>3</sub>]], [[Na2SO4|Na<sub>2</sub>SO<sub>4</sub>]], NaCl, [[NaHCO3|NaHCO<sub>3</sub>]], and [[NaOH]] || Na<sup>+</sup> can partially replace K<sup>+</sup> in some plant functions but K<sup>+</sup> is still an essential nutrient.{{sfn|Douglas|1985|p={{pn|date=March 2025}}}}
|-
| [[Vanadium]] || Non-essential micronutrient || [[Vanadyl ion|VO<sup>2+</sup>]] || 0 || Trace, undetermined || [[VOSO4|VOSO<sub>4</sub>]] || Beneficial for rhizobial [[Nitrogen fixation|N<sub>2</sub> fixation]].{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}}
|-
| [[Lithium]] || Non-essential micronutrient || Li<sup>+</sup> || 0 || Undetermined || [[Li2SO4|Li<sub>2</sub>SO<sub>4</sub>]], [[LiCl]], and [[LiOH]] || Li<sup>+</sup> can increase the chlorophyll content of some plants (e.g. [[potato]] and [[Capsicum|pepper plants]]).{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}}
|}

===Organic hydroponic solutions===
{{Main|Organic hydroponics}}

[[Organic fertilizer]]s can be used to supplement or entirely replace the [[inorganic compound]]s used in [[Dennis Robert Hoagland#Hewitt's Table 30A|conventional hydroponic solutions]].{{sfn|Douglas|1985|p={{pn|date=March 2025}}}}{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} However, using organic fertilizers introduces a number of challenges that are not easily resolved. Examples include:
* organic fertilizers are highly variable in their nutritional compositions in terms of [[Mineral (nutrient)|minerals]] and different organic and inorganic [[chemical species|species]]. Even similar materials can differ significantly based on their source (e.g. the quality of [[manure]] varies based on an animal's diet).
* organic fertilizers are often sourced from animal byproducts, making [[Transmission (medicine)|disease transmission]] a serious concern for plants grown for human consumption or animal [[forage]].
* organic fertilizers are often [[particulate]], contain environmental [[pollutant]]s, and can clog [[#Substrates (growing support materials)|substrates]] or other growing equipment. [[Sieve|Sieving]] or [[mill (grinding)|milling]] the organic materials to fine dusts is often necessary.
* [[Biochemistry|biochemical]] [[Biodegradation|degradation]] and conversion processes of complex organic materials can make their mineral ingredients [[Bioavailability (soil)|available]] to plants.
* some organic materials (i.e. particularly [[manures]] and [[offal]]) can further degrade to emit foul odors under [[Anaerobic digestion|anaerobic conditions]] or emit [[nanoparticle]]s.
* many organic molecules (i.e. [[sugar]]s) demand additional oxygen during aerobic degradation, which is essential for [[cellular respiration]] in the plant roots.
* organic compounds (i.e. sugars, [[vitamin]]s, a.o.) are not necessary for normal plant nutrition.<ref>{{cite journal |last1=Murashige |first1=Toshio |last2=Skoog |first2=Folke |title=A Revised Medium for Rapid Growth and Bio Assays with Tobacco Tissue Cultures |journal=Physiologia Plantarum |date=July 1962 |volume=15 |issue=3 |pages=473–497 |doi=10.1111/j.1399-3054.1962.tb08052.x |bibcode=1962PPlan..15..473M }}</ref>

Nevertheless, if precautions are taken, organic fertilizers can be used successfully in hydroponics.{{sfn|Douglas|1985|p={{pn|date=March 2025}}}}{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}}

====Organically sourced macronutrients====
Examples of suitable materials, with their average nutritional contents tabulated in terms of percent dried mass, are listed in the following table.{{sfn|Douglas|1985|p={{pn|date=March 2025}}}}
{| class="wikitable"
|-
! Organic material !! [[Nitrogen fertilizers|N]] !! [[Phosphate fertilizer|P<sub>2</sub>O<sub>5</sub>]] !! [[Fertilizer#Potassium fertilizers|K<sub>2</sub>O]] !! [[Calcium|CaO]] !! [[Magnesium|MgO]] !! [[Sulfur|SO<sub>2</sub>]] !! Comment
|-
| [[Bloodmeal]] || 13.0% || 2.0% || 1.0% || 0.5%|| – || – ||
|-
| [[Bone ash]]es || – || 35.0% || – || 46.0% || 1.0% || 0.5% ||
|-
| [[Bonemeal]] || 4.0% || 22.5% || – || 33.0% || 0.5% || 0.5% ||
|-
| [[Hoof]] / [[Horn (anatomy)|Horn]] meal || 14.0% || 1.0% || – || 2.5% || – || 2.0% ||
|-
| [[Fishmeal]] || 9.5% || 7.0% || – || 0.5% || – || – ||
|-
| [[Wool]] waste || 3.5% || 0.5% || 2.0% || 0.5% || – || – ||
|-
| [[Wood ash]]es || – || 2.0% || 5.0% || 33.0% || 3.5% || 1.0% ||
|-
| [[Cottonseed]] ashes || – || 5.5% || 27.0% || 9.5% || 5.0% || 2.5% ||
|-
| [[Cottonseed meal]]|| 7.0% || 3.0% || 2.0% || 0.5% || 0.5% || – ||
|-
| Dried [[locust]] or [[grasshopper]] || 10.0% || 1.5% || 0.5% || 0.5% || – || – ||
|-
| [[Leather]] waste || 5.5% to 22% || – || – || – || – || – || [[Mill (grinding)|Milled]] to a fine dust.{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}}
|-
| [[Seaweed fertiliser|Kelp meal, liquid seaweed]] || 1% || – || 12% || – || – || – || Commercial products available.
|-
| [[Poultry]] manure || 2% to 5% || 2.5% to 3% || 1.3% to 3% || 4.0% || 1.0% || 2.0% || A [[Compost tea|liquid compost]] which is [[sieve]]d to remove solids and checked for [[pathogen]]s.{{sfn|Douglas|1985|p={{pn|date=March 2025}}}}
|-
| [[Sheep]] manure|| 2.0% || 1.5% || 3.0% || 4.0% || 2.0% || 1.5% || Same as poultry manure.
|-
| [[Goat]] manure || 1.5% || 1.5% || 3.0% || 2.0% || – || – || Same as poultry manure.
|-
| [[Horse]] manure || 3% to 6% || 1.5% || 2% to 5% || 1.5% || 1.0% || 0.5% || Same as poultry manure.
|-
| [[Cow]] manure || 2.0% || 1.5% || 2.0% || 4.0% || 1.1% || 0.5% || Same as poultry manure.
|-
| [[Bat]] [[guano]]|| 8.0% || 40% || 29% || Trace || Trace || Trace || High in micronutrients.{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} Commercially available.
|-
| Bird guano|| 13% || 8% || 20% || Trace || Trace || Trace || High in micronutrients. Commercially available.
|}

====Organically sourced micronutrients====
Micronutrients can be sourced from organic fertilizers as well. For example, [[compost]]ed [[conifer|pine]] bark is high in [[manganese]] and is sometimes used to fulfill that mineral requirement in [[Dennis Robert Hoagland#Hewitt's Table_30A|conventional hydroponic solutions]].{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} To satisfy requirements for [[National Organic Program]]s, pulverized, unrefined [[mineral]]s (e.g. [[Gypsum]], [[Calcite]], and [[glauconite]]) can also be added to satisfy a plant's nutritional needs.

===Additives===
Compounds can be added in both organic and conventional hydroponic systems to improve nutrition acquisition and uptake by the plant''.'' Chelating agents and humic acid have been shown to increase nutrient uptake.<ref>{{cite journal|last1=Adania|first1=Fabrizio|last2=Genevinia|first2=Pierluigi|last3=Zaccheoa|first3=Patrizia|last4=Zocchia|first4=Graziano|date=1998|title=The effect of commercial humic acid on tomato plant growth and mineral nutrition|journal=Journal of Plant Nutrition|volume=21|issue=3|pages=561–575|doi=10.1080/01904169809365424|bibcode=1998JPlaN..21..561A }}</ref>{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} Additionally, plant growth promoting rhizobacteria (PGPR), which are regularly utilized in field and greenhouse agriculture, have been shown to benefit hydroponic plant growth development and nutrient acquisition.<ref>{{cite journal |last1=Lee |first1=Seungjun |last2=Lee |first2=Jiyoung |title=Beneficial bacteria and fungi in hydroponic systems: Types and characteristics of hydroponic food production methods |journal=Scientia Horticulturae |date=November 2015 |volume=195 |pages=206–215 |doi=10.1016/j.scienta.2015.09.011 |bibcode=2015ScHor.195..206L }}</ref> Some PGPR are known to increase nitrogen fixation. While nitrogen is generally abundant in hydroponic systems with properly maintained fertilizer regimens, ''Azospirillum'' and ''Azotobacter'' genera can help maintain mobilized forms of nitrogen in systems with higher microbial growth in the rhizosphere.<ref name=":5">{{Cite thesis |degree=Bachelor |last=Soderstrom |first=Linus |date=2020|title=Plant-Growth Promoting Rhizobacteria in Soilless Cannabis Cropping Systems |url=https://stud.epsilon.slu.se/16079/11/soderstrom_l_200923.pdf |publisher=Sveriges lantbruksuniversitet}}</ref> Traditional fertilizer methods often lead to high accumulated concentrations of nitrate within plant tissue at harvest. ''Rhodopseudo-monas palustris'' has been shown to increase nitrogen use efficiency, increase yield, and decrease nitrate concentration by 88% at harvest compared to traditional hydroponic fertilizer methods in leafy greens.<ref>{{Cite journal |author=ShuHua Hsu |author2=KaiJiun Lo |author3=Wei Fang |author4=HuuSheng Lur |author5=ChiTe Liu |date=2015|title=Application of phototrophic bacterial inoculant to reduce nitrate content in hydroponic leafy vegetables|url=https://www.cabdirect.org/cabdirect/abstract/20153203178 |url-access=subscription |journal=Crop, Environment, and Bioinformatics|volume=12|pages=30–41}}</ref>  Many ''Bacillus'' spp., ''Pseudomonas'' spp. and ''Streptomyces'' spp. convert forms of phosphorus in the soil that are unavailable to the plant into soluble anions by decreasing soil pH, releasing phosphorus bound in chelated form that is available in a wider pH range, and mineralizing organic phosphorus.<ref name=":5" />

Some studies have found that ''Bacillus'' inoculants allow hydroponic leaf lettuce to overcome high salt stress that would otherwise reduce growth.<ref>{{cite journal |last1=Moncada |first1=Alessandra |last2=Vetrano |first2=Filippo |last3=Miceli |first3=Alessandro |title=Alleviation of Salt Stress by Plant Growth-Promoting Bacteria in Hydroponic Leaf Lettuce |journal=Agronomy |date=6 October 2020 |volume=10 |issue=10 |page=1523 |doi=10.3390/agronomy10101523 |doi-access=free |bibcode=2020Agron..10.1523M |hdl=10447/437141|hdl-access=free }}</ref> This can be especially beneficial in regions with high electrical conductivity or salt content in their water source. This could potentially avoid costly reverse osmosis filtration systems while maintaining high crop yield.

===Tools===
====Common equipment====
Managing nutrient concentrations, oxygen saturation, and pH values within acceptable ranges is essential for successful hydroponic [[horticulture]]. Common tools used to manage hydroponic solutions include:
* [[Electrical conductivity meter]]s, a tool which estimates nutrient ppm by measuring how well a solution transmits an [[electric current]].
* [[pH meter]], a tool that uses an electric current to determine the concentration of [[hydrogen ion]]s in solution.
* [[Clark electrode|Oxygen electrode]], an electrochemical sensor for determining the oxygen concentration in solution.
* [[Litmus paper]], disposable [[pH indicator]] strips that determine hydrogen ion concentrations by color changing [[chemical reaction]].
* [[Graduated cylinder]]s or [[measuring spoon]]s to measure out premixed, commercial hydroponic solutions.

====Equipment====
Chemical equipment can also be used to perform accurate [[chemical analysis|chemical analyses]] of nutrient solutions. Examples include:{{sfn|Douglas|1985|p={{pn|date=March 2025}}}}
* [[Weighing scale|Balances]] for accurately measuring materials.
* [[Laboratory glassware]], such as [[burette]]s and [[pipette]]s, for performing [[titration]]s.
* [[Colorimeter (chemistry)|Colorimeters]] for solution tests which apply the [[Beer–Lambert law]].
* [[Spectrophotometry|Spectrophotometer]] to measure the concentrations of the key parameter nitrate and other nutrients, such as phosphate, sulfate or iron.
* [[Containers]] for growing and storing the plants.

Using chemical equipment for hydroponic solutions can be beneficial to growers of any background because nutrient solutions are often reusable.<ref name=Reuse /> Because nutrient solutions are virtually never completely depleted, and should never be due to the unacceptably low [[osmotic pressure]] that would result, re-fortification of old solutions with new nutrients can save growers money and can control [[point source pollution]], a common source for the [[eutrophication]] of nearby lakes and streams.<ref name="Reuse">{{cite journal|last1=Kumar|first1=Ramasamy Rajesh|last2=Cho|first2=Jae Young|title=Reuse of hydroponic waste solution|journal=Environmental Science and Pollution Research|date=2014|volume=21|issue=16|pages=9569–9577|doi=10.1007/s11356-014-3024-3|pmid=24838258|bibcode=2014ESPR...21.9569K }}</ref>

====Software====
Although pre-mixed concentrated nutrient solutions are generally purchased from commercial nutrient manufacturers by hydroponic hobbyists and small commercial growers, several tools exist to help anyone prepare their own solutions without extensive knowledge about chemistry. The free and open source tools HydroBuddy<ref>{{cite web|url=https://scienceinhydroponics.com/2016/03/the-first-free-hydroponic-nutrient-calculator-program-o.html|title=HydroBuddy v1.62: The First Free Open Source Hydroponic Nutrient Calculator Program Available Online|date=Mar 30, 2016|website=scienceinhydroponics.com|language=en-US|access-date=Nov 22, 2018}}</ref> and HydroCal<ref>{{cite web|url=https://sourceforge.net/projects/hydrocal/|title=HydroCal: Hydroponic Nutrient Formula Calculator|date=Feb 2, 2010|website=SourceForge|language=en}}</ref> have been created by professional chemists to help any hydroponics grower prepare their own nutrient solutions. The first program is available for Windows, Mac and Linux while the second one can be used through a simple JavaScript interface. Both programs allow for basic nutrient solution preparation although HydroBuddy provides added functionality to use and save custom substances, save formulations and predict electrical conductivity values.

===Mixing solutions===
Often mixing hydroponic solutions using individual salts is impractical for hobbyists or small-scale commercial growers because commercial products are available at reasonable prices. However, even when buying commercial products, multi-component fertilizers are popular. Often these products are bought as three part formulas which emphasize certain nutritional roles. For example, solutions for vegetative growth (i.e. high in nitrogen), flowering (i.e. high in potassium and phosphorus), and micronutrient solutions (i.e. with trace minerals) are popular. The timing and application of these multi-part fertilizers should coincide with a plant's growth stage. For example, at the end of an [[annual plant]]'s [[Biological life cycle|life cycle]], a plant should be restricted from high nitrogen fertilizers. In most plants, nitrogen restriction inhibits vegetative growth and helps [[Flowering transition|induce flowering]].{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}}

==Additional improvements==

[[File:Young plants in veg.jpg|thumb|Young cannabis plants in an ebb-and-flow grow room, Alaska.]]

=== Growrooms ===
With pest problems reduced and nutrients constantly fed to the roots, productivity in hydroponics is high; however, growers can further increase yield by manipulating a plant's environment by constructing sophisticated [[growroom]]s.<ref name="Air">{{cite journal|last1=Peiro|first1=Enrique|last2=Pannico|first2=Antonio|last3=Colleoni|first3=Sebastian George|last4=Bucchieri|first4=Lorenzo|last5=Rouphael|first5=Youssef|last6=De Pascale|first6=Stefania|last7=Paradiso|first7=Roberta|last8=Godia|first8=Francesc|title=Air distribution in a fully-closed higher plant growth chamber impacts crop performance of hydroponically-grown Lettuce|journal=Frontiers in Plant Science|date=2020|volume=11|issue=537|page=537 |doi=10.3389/fpls.2020.00537|pmc=7237739|pmid=32477383|bibcode=2020FrPS...11..537P |doi-access=free }}</ref>

===CO<sub>2</sub> enrichment===
{{Main|Carbon dioxide#Applications}}
To increase yield further, some sealed greenhouses inject [[carbon dioxide|CO<sub>2</sub>]] into their environment to help improve growth and plant fertility.

== Crops grown ==
Hydroponic crops are chosen based on the [[Demand|market demand]] for a crop, environmental suitability, growth cycles, root structures, and plant growth characteristics that make them good candidates for soilless cultivation.{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}} [[Leaf vegetable|Leafy greens]] like lettuce, spinach, and kale are grown because they have a short growing cycle of as little as 30-50 days, have high market value, and require minimal space.<ref name=":9">{{Citation |last1=Asaduzzaman |first1=Md. |title=Influence of Soilless Culture Substrate on Improvement of Yield and Produce Quality of Horticultural Crops |date=2015-02-25 |work=Soilless Culture - Use of Substrates for the Production of Quality Horticultural Crops |editor-last=Asaduzzaman |editor-first=Md. |url=https://www.intechopen.com/chapters/48098 |access-date=2025-03-04 |publisher=InTech |language=en |doi=10.5772/59708 |isbn=978-953-51-1739-1 |last2=Saifullah |first2=Md. |last3=Mollick |first3=A.K.M. Salim Reza |last4=Hossain |first4=Md. Mokter |last5=Halim |first5=G.M.A. |last6=Asao |first6=Toshiki}}</ref>

Vegetable crops like tomatoes, peppers, and cucumbers are also widely grown in hydroponics. These crops are successful due to a hydroponic system's ability to precisely control each crop's temperature, humidity, and light requirements. This control optimizes crop yield and maintains the quality and nutrition of the plants grown.{{sfn|Jones Jr.|2016|p={{pn|date=March 2025}}}}

[[Herb|Culinary herbs]] such as basil, mint, cilantro, rosemary, and parsley are popular to grow using hydroponics due to their demand from consumers and profitability. Most herbs also grow quickly, with a growth cycle of 25-40 days per harvest for herbs like basil, mint, and cilantro.<ref name=":7">{{cite book |doi=10.1201/9781003133254 |title=Hydroponic Food Production |date=2022 |last1=Resh |first1=Howard M. |isbn=978-1-003-13325-4 }}{{pn|date=March 2025}}</ref> Longer growing herbs such as rosemary can be harvested multiple times from the same plant. This eliminates the need for new seedlings and extends the production window for each plant.<ref name=":7" />

== Urban hydroponics ==
Urban hydroponics refers to the use of soilless cultivation systems in city environments, including apartments, rooftops, and other indoor spaces. These systems have been explored in response to challenges related to urban food access. According to the [[United States Department of Agriculture]], more than 19 million people in the United States live in low-income neighborhoods with limited access to supermarkets or large grocery stores, areas often referred to as [[Food desert|food deserts]].<ref>{{Cite web |title=Food Access Research Atlas {{!}} Economic Research Service |url=https://www.ers.usda.gov/data-products/food-access-research-atlas |access-date=2025-05-03 |website=www.ers.usda.gov}}</ref> In these contexts, hydroponic systems can be used as a method to grow vegetables such as lettuce, spinach, and herbs indoors.

Urban hydroponic systems are generally designed to operate within small spaces. Commercially available units include vertical towers, countertop kits, and window-mounted structures, many of which rely on artificial lighting and water circulation to deliver nutrients directly to plant roots.<ref name=":7" /> These configurations are intended to support plant growth in environments with limited natural sunlight and no access to soil.

Some hydroponic systems are marketed toward individual consumers and households. While larger systems may require significant investment, smaller-scale models are available for individual use. Reports suggest that such systems can produce a range of crops year-round, though yield and cost-efficiency vary by setup and user experience.<ref>{{Cite journal |last1=Zhang |first1=Jingmiao |last2=Hori |first2=Naruhito |last3=Takemura |first3=Akio |date=2020-12-20 |title=Thermal and time regularities during oilseed rape straw liquefaction process to produce bio-polyol |url=https://www.sciencedirect.com/science/article/abs/pii/S0959652620340609 |journal=Journal of Cleaner Production |volume=277 |article-number=124015 |doi=10.1016/j.jclepro.2020.124015 |bibcode=2020JCPro.27724015Z |issn=0959-6526|url-access=subscription }}</ref>

Hydroponic systems have also been studied for their resource efficiency. In urban settings, [[Local food|locally grown produce]] using hydroponics may reduce the need for long-distance transportation of produce, though the overall environmental impact depends on multiple factors, including energy use for lighting and [[Heating, ventilation, and air conditioning|climate control]].

As global [[urbanization]] continues, hydroponics has been included in urban food systems and localized agriculture discussions. The United Nations projects that by 2050, nearly 70 percent of the global population will live in urban areas, a demographic trend contributing to interest in alternative food production methods such as hydroponics.<ref>{{Cite web |title=World Urbanization Prospects |url=https://population.un.org/wup/ |access-date=2025-05-03 |website=population.un.org}}</ref>

==See also==
{{Portal|Agriculture|Gardening}}
* [[Aeroponics]]
* [[Anthroponics]]
* [[Aquaponics]]
* [[Digeponics]]
* [[Fogponics]]
* [[Folkewall]]
* [[Grow box]]
* [[Growroom]]
* [[Nutrient film technique]]
* [[Organoponics]]
* [[Passive hydroponics]]
* [[Plant factory]]
* [[Plant nutrition]]
* [[Plant pathology]]
* [[Root rot]]
* [[Vertical farming]]
* [[Xeriscaping]]

==References==
{{Reflist|30em}}

==Sources==
* {{cite book |last1=Douglas |first1=James Sholto |title=Hydroponics: The Bengal System: with Notes on Other Methods of Soilless Cultivation |date=1975 |publisher=Oxford University Press |isbn=978-0-19-560530-3 }}
* {{cite book |last1=Douglas |first1=James Sholto |title=Advanced Guide to Hydroponics |date=1985 |publisher=Pelham |isbn=978-0-7207-1571-2 |oclc=1341823405 }}
* {{cite book |doi=10.1201/9780849331671 |title=Hydroponics |date=2016 |last1=Jones Jr. |first1=J. Benton |isbn=978-1-4200-3770-8 }}

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