Hydroponics

Summary

Hydroponics uses varied scientific and technological processes to cultivate plants without soils usually associated with agriculture. Throughout history, humans have delivered nutrients directly to plant roots with water. Based on that principle, modern hydroponics has diverse commercial and utilitarian agriculture applications. Hydroponics supplies food to military personnel in places where agricultural resources are limited because of climate and terrain. Astronauts eat fresh vegetables grown with hydroponics in space. Food security is bolstered by the availability of substantial yields year-round as assured by hydroponics, providing people access to nutrients and relief from hunger. Agribusinesses sell hydroponic crops and equipment to consumers. Many scientific and educational curricula incorporate hydroponic lessons.

Definition and Basic Principles

Hydroponics is the scientific use of chemicals, organic and inorganic materials, and technology to grow plants independently of soil. Solutions composed of water and dissolved minerals and elements provide essential macronutrients and micronutrients and supplement oxygen and light necessary for plant growth. Plant roots absorb nutrients that are supplied through various methods. Some hydroponic systems involve suspending roots in liquid solutions. Other hydroponic techniques periodically wash or spray roots with solutions. Methods also utilize containers filled with substrates, such as gravel, where roots are flooded with nutrient solutions. Hydroponics is practiced in greenhouses, where temperatures and lighting can be regulated, and outdoors, where milder climates pose few natural detriments to plants.

Hydroponics enables agriculturists to grow crops continually without relying on weather, precipitation, and other factors associated with natural growing seasons. These systems permit agricultural production in otherwise unsuitable settings for crop cultivation, such as congested cities, deserts, and mountains. Hydroponics is convenient, producing foods in all seasons. Plants can be grown closely together because root growth does not spread like soil-based plant roots extending to seek nutrients and water. Agriculturists can grow crops that are not indigenous to areas, such as tropical fruits. Growth typically occurs more quickly with hydroponics than in soil because plants invest energy in maturing rather than competing for resources, resulting in large yields. Many hydroponic systems recycle water that is not absorbed by roots and use it for other purposes. Crops cultivated with hydroponic systems are usually safer for consumers than field-grown crops because their exposure to soil-transmitted diseases has been minimized.

Negative aspects of hydroponics include costs associated with acquiring equipment and supplies. Automation and computerized systems require substantial investments in machinery, software, and training personnel to operate them.

Background and History

Records indicate people cultivated plants using water instead of soil in ancient Mesopotamia, Egypt, and Rome. Aztecs in Mexico invented floating barges and chinampas to grow food on lakes because they lacked suitable agricultural land. In the mid-nineteenth century, German botanist Julius von Sachs and German agrochemist Wilhelm Knop experimented with combining minerals with water to nourish plants.

During the 1920s, University of California, Berkeley, plant nutrition professor Dennis R. Hoagland studied how roots absorb nutrients. William F. Gericke, also a professor at the University of California, Berkeley, cultivated tomatoes in tanks of mineral-rich solution and discussed his research in a February 1937 Science article, noting colleague William A. Setchell referred to that process as hydroponics, representing Greek vocabulary: hydro (water) and ponos (work).

In the 1940s, the United States (US) military utilized hydroponics to provide sustenance to World War II soldiers in the Pacific. Oil companies built hydroponic gardens on Caribbean islands to feed employees who were extracting natural resources in that region. The US Army established a hydroponics branch to supply troops serving in the Korean War in the early 1950s, growing eight million pounds of food.

By mid-century, researchers began incorporating plastic equipment in hydroponic systems. Engineers innovated better pumps and devices, automating some hydroponic processes with computers. By the 1970s, new methods, including drip-irrigation systems and the nutrient film technique (NFT), had been created by English scientist Allen Cooper, which helped commercial hydroponics expand globally. The United Nations Food and Agriculture Organization (FAO) funded hydroponic programs in areas experiencing food crises. Scientists continued devising new techniques, such as aerohydroponics, in the late twentieth century. Advances have been made in the twenty-first century in machine learning and automation used to monitor and pick crops. Artificial intelligence is used in hydroponics to analyze and adapt to environmental changes, predict growth and harvesting models, and detect disease.

How It Works

Hydroponics. Hydroponic processes represent examples of controlled environment agriculture in which plant cultivation involves technology, such as greenhouses, enabling growers to stabilize conditions. Most hydroponic systems function with basic components that supply oxygen and nutrients necessary to sustain plants until they have matured for harvest. Electrical or solar-powered lights, fans, heaters, and pumps regulate temperatures and ventilation for plant respiration, water flow, and photosynthesis, impacting plant growth. Each hydroponic system incorporates variations of equipment and methods according to growers' resources and goals. Styrofoam, wood, glass, and plastic are materials used to construct hydroponic systems.

Basic hydroponic procedures involve placing seeds in substrates that consist of organic materials, such as coconut fibers, rice hulls, sawdust, and peat moss, or inorganic mediums including gravel, pumice, perlite, rock wool, or vermiculite. After roots emerge during germination, growers keep seedlings in substrates or remove them depending on which hydroponic method is selected for cultivation. Roots undergo varying durations of exposure to nutrient solutions to absorb macronutrients and micronutrients. Most hydroponic processes utilize either an open, or non-recirculating, system or a closed system, referred to as recirculating, depending on whether nutrient solution contacts roots once and is discarded or is kept for consistent or repeated use.

Water-Culture Techniques. These hydroponic methods, which are frequently used to cultivate plants that quickly attain maturity, involve roots constantly being suspended in a nutrient solution. Water-culture hydroponic techniques are often utilized to grow lettuce crops. For the raft culture technique, growers place plants on platforms drilled with holes to pull roots through so roots can be submerged in pools of nutrient solution on which the platforms float. In the dynamic root floating technique, roots closest to the plant are kept dry to supply oxygen to the plant. The lower roots are constantly exposed to nutrient solutions and absorb those minerals and elements to nourish the plant.

Pumps and air stones oxygenate nutrient solutions so that roots are aerated. Lighting is essential for plants to undergo photosynthesis above the solution surface. Growers monitor nutrient solutions' pH levels and the presence of any algae, which might harm roots, interfere with their adsorption of nutrients, and impede plant growth. Growers also replenish fluids lost to evaporation.

Nutrient Solution Culture (NSC) Methods. Several forms of NSC are utilized to feed plants. Continuous-flow NSC involves nutrient solutions being poured into a trough and constantly moving through roots. Nutrient solutions contact roots less frequently in intermittent-flow NSC. The drip NSC technique delivers nutrient solutions through tubing and emitters that dispense water on the substrate near the roots. Some drip systems recycle nutrient solution. The wick system utilizes strings that extend from substrates to a reservoir filled with nutrient solution.

In the ebb-and-flow method, the nutrient solution contacts roots in cycles after flooding trays containing roots and substrates, drains, and returns them to a tank for additional delivery. Timers control pump mechanisms, which move nutrient solutions. Aquaponics systems transport water from ponds or greenhouses, where fish tanks are kept, to greenhouses, where plants are grown, so that waste from the fish can provide nutrients for plants.

Nutrient Film Technique (NFT). This closed system continually pumps nutrient solutions into a channel placed at an angle where roots hang under plants supported from above by platforms or other equipment. No substrates are used. The solution contacting roots is delivered as a watery film to ensure roots will receive sufficient oxygen. The hydroponic trough system uses a reservoir, which includes a filtering device to strain contaminants from nutrient solutions. Resembling NFT methods, aeroponics does not rely on substrates. Sprayers attached to timers continually dispense nutrient solutions on roots suspended in air below plants.

Applications and Products

Nutrition. Hydroponics enables ample production of food supplies that meet nutritional needs for vitamins, antioxidants, and amino acids crucial for maintaining people's bodies. These techniques aid hunger relief in arid regions where climate change is associated with expanding desertification and loss of arable land, threatening food security. Hydroponic cultivation provides rural and urban populations access to affordable, fresh, healthy food despite losing access to traditional agricultural supplies due to political, economic, or military crises, natural disasters, or famines. Various hydroponic techniques can be applied to produce crops with increased levels of calcium, potassium, and other elements essential to sustain health. Hydroponic processes can be designed to grow food with appealing tastes, textures, and appearances.

Agribusiness. Hydroponics generates profits for commercial sellers of crops, manufacturers of hydroponic equipment, nutrient solutions, and supplies, and wholesalers and retailers that distribute hydroponic merchandise to consumers. Agribusinesses create and market hydroponic greenhouses of varying sizes, including small growing containers, such as AeroGarden, for use inside homes to consumers. Shipping containers have been outfitted with all the equipment to set up self-contained hydroponics operations anywhere electricity is available. Many florists grow stock cultivated with hydroponics at their stores. Internationally, the number of hydroponic businesses has expanded on all continents except Antarctica, contributing to countries' economies. Advanced Nutrients, one of the most successful hydroponic businesses internationally, sells its merchandise to customers in over one hundred countries. Some hydroponic companies develop and sell smartphone applications to perform hydroponic functions, such as General Hydroponics' calculator for preparing nutrient solutions.

Education. Students at various levels, from elementary through graduate school, often study hydroponics in science classes. Some courses may discuss hydroponics to explain basic scientific principles, such as how roots absorb nutrients, while others may focus on special topics, such as genetics. Students frequently investigate aspects of hydroponics for science fair competitions or projects for the Future Farmers of America. Teachers instructing Advanced Placement biology courses often encourage students to develop hydroponic systems to comprehend concepts associated with plant growth and nutrition. Some school cafeterias use foods grown on their campuses, or students sell products, cultivated with hydroponic techniques for fund-raisers. Universities sometimes award funds to students' innovative hydroponic projects, especially those with humanitarian applications. The Denver Botanic Gardens and other botanical centers have offered hydroponic classes.

Military and Exploration. Military troops benefit from the establishment of hydroponic systems near bases and battlefields to produce fresh vegetables for rations regardless of soil and climate conditions in those areas. Hydroponic applications for military usage enable crews on vessels undergoing lengthy sea voyages to grow foods between ports. Veterans with hydroponic experience or who complete Veterans Sustainable Agriculture Training or similar programs are often sought out for employment in that field. The ability to grow foods without soil nourishes people traveling by submarine, whether for military or scientific reasons. Workers in remote locations, such as offshore oil and natural gas rigs, eat meals incorporating hydroponic produce grown at those sites.

Scientists conducting research at Antarctic stations rely on hydroponics for sustenance and as a method to recycle, purify, and store water. The South Pole Food Growth Chamber, designed by the Controlled Environment Agriculture Center at the University of Arizona, uses NFT methods and is automated with an Argus climate-control system. The National Aeronautics and Space Administration (NASA) funds projects, such as Controlled Ecological Life Support Systems (CELSS), in which hydroponic plants remove carbon dioxide and pollutants while producing food on spacecraft. Researchers have investigated using hydroponics for long-term missions.

Urban Planning. Some twenty-first-century architecture incorporates hydroponics to feed increasing populations, particularly in urban areas. Rooftops are popular sites for hydroponic systems where land is unavailable for gardens. These urban farms grow large yields of basic vegetable crops and supply fresh produce to residents who might otherwise not have access to those foods. Vertical farming techniques inspired proposals applying hydroponics. In New York City, Dickson Despommier, a Columbia University microbiologist, introduced his idea to renovate almost two thousand empty structures with hydroponic equipment. Several large vertical farms operate in the US. In 2022, Upward Farms began constructing the world's largest indoor vertical farm, an aquaponics facility in Luzerne County, Pennsylvania, which hoped to produce organic produce and sustainably raised fish. Unfortunately, this project was forced to shut down in 2023, with the company admitting the complexities of vertical farming were too great for such a large-scale operation. The Seoul Commune 2026 in South Korea presented another vertical farming proposal. When initially proposed, this project was intended to involve covering skyscrapers, some fifty floors high, with supports for plants. Nutrients delivered by fog machines and irrigation technology to roots would nourish plants growing on those garden buildings. This, however, is another example of a vertical farming operation that never came to fruition. Proponents of hydroponics note that by establishing more hydroponic gardens on rooftops located in close proximity to supermarkets, produce can reach consumers in a much fresher and less damaged state than having to be shipped across distances from traditional farms.

Tourism. Some hotels, especially in exotic locales, apply hydroponics for agricultural and aesthetic uses. In Anguilla in the Caribbean, the CuisinArt Resort and Spa grows hydroponic herbs, vegetables, and flowers. Guests can tour areas with hydroponic equipment to see where food served in the hotel's restaurant is grown. These businesses sometimes sell hydroponic products, often identified by the resort brand, to cruise ships docking nearby or to markets. Visitors can tour hydroponic displays at Epcot's Land Pavilion in Orlando, Florida. Zoos occasionally utilize hydroponic processes to cultivate grain and grass to feed animals.

Careers and Course Work

Students interested in professions associated with hydroponics can complete diverse educational programs to pursue their career goals. Many entry-level hydroponic positions are available to people with high school educations or associate's degrees. Some employers seeking qualified workers to build and maintain hydroponic systems expect candidates to have completed basic horticultural courses at technical schools, community colleges, or universities, preparing them to cultivate plants and assemble equipment. Experience working for landscaping businesses, farms, or other positions that involve tending plants enhances one's employability. One can sometimes find available positions at gardening businesses that use hydroponics to grow crops and ornamental plants to sell to consumers and markets. Resorts, botanical gardens, and theme parks hire people with educational and work experience to establish and maintain hydroponic gardens.

Government, academic, and industrial employers that staff scientific and technological positions focusing on hydroponics usually require a minimum of a Bachelor of Science degree in a related field. Candidates can acquire basic knowledge of plant cultivation by studying horticulture, botany, agriculture, or subjects applicable to hydroponics. Those seeking research positions typically need to earn advanced degrees—a Master's or Doctorate—in relevant subjects, acquiring expertise that will benefit the quality of their employers' services and hydroponic products. Agricultural engineering, computer science, or robotics courses prepare employees for positions designing hydroponic structures, machinery, and automation software. Candidates with advanced education or hydroponic experience have credentials for many positions as administrators or educators in schools, experiment stations, extension services, or government agencies.

Social Context and Future Prospects

In the twenty-first century, hydroponics continued to provide humanitarian and commercial benefits. The Hydroponic Merchants Association stated in 2004 that hydroponic greenhouses grew 55,000 acres of vegetables internationally, of which 5,800 acres in North America produced tomatoes, peppers, and cucumbers valued at $2.4 billion. Thanks to increasing demand and advances in hydroponic technology, the global market had grown to $9.5 billion in 2024 and was projected to grow more than 11.3 percent annually. Industry experts suggest that hydroponics, universal to diverse cultures, will continue to expand for several reasons, including depletion of arable lands caused by natural disasters and global warming, expenses associated with machinery and operation of conventional agriculture, and public disapproval of bioengineering related to field crops. 

Hydroponics presents food-security solutions to the increasing population, estimated to reach nine billion people by 2050. With the increased legalization of medicinal and recreational marijuana in many US states, a common and once clandestine use for hydroponics technology has been lent a newfound legitimacy. At the same time, authorities struggle with policing legitimate sellers of hydroponic tools and equipment in states where marijuana use has not been legalized, as experience has shown that most of the items sold go toward the purpose of growing marijuana at home. 

While beneficial for numerous reasons, hydroponics has also been the source of debate in the community of organic farmers in the US. Many argued that, due to the lack of soil use, products resulting from the process should not be called organic. After considerable disagreement, a court ruled in 2021 that the US Department of Agriculture (USDA) was correct in allowing hydroponic operations to be certified organic by exempting them from the requirement that producers build soil fertility. Several trends have appeared in the hydroponics market as the twenty-first century has progressed. Liquid hydroponic systems believed to send nutrients to plants more efficiently have been developed. Access to new and exotic foods has increased. The Internet of Things and blockchain technology have increased profits while minimizing costs, making predicting and evaluating plant health and growth more manageable. Finally, hydroponics has seen increased support from global governments keen on sustainability measures. 

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