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The word hydroponics has its derivation from the combining of two Greek words, hydro meaning water and ponos meaning labor, i.e., working water. The word first appeared in a scientific magazine article (Science, Feb 178:1) published in 1937 and authored by W.F. Gericke, who had accepted this word as was suggested by Dr. W.A. Setchell at the University of California. Dr. Gericke began experimenting with hydroponic growing techniques in the late 1920s and then published one of the early books on soilless growing (Gericke, 1940). Later he suggested that the ability to produce crops hydroponically would no longer be "chained to the soil but certain commercial crops could be grown in larger quantities without soil in basins containing solutions of plant food." What Dr. Gericke failed to foresee was that hydroponics would in the future be essentially confined to its application in enclosed environments for growing high cash value crops and would not find its way into the production of a wide range of commercial crops in open environments.

Hydroponic Definitions

The author went to three dictionaries and three encyclopedias to find how hydroponics is defined. Webster's New World College Dictionary, Fourth Edition, 1999, defines hydroponics as "the science of growing or the production of plants in nutrient-rich solutions or moist inert material, instead of soil"; the Random House Webster's College Dictionary, 1999, as "the cultivation of plants by placing the roots in liquid nutrient solutions rather than in soils; soilless growth of plants"; and The Oxford English Dictionary, 2nd Edition, 1989, as "the process of growing plants without soil, in beds of sand, gravel, or similar supporting material flooded with nutrient solutions."

In the Encyclopedia Americana, International Edition, 2000, hydroponics is defined as "the practice of growing plants in liquid nutrient cultures rather than in soil," in The New Encyclopaedia Britannica, 1997 as "the cultivation of plants in nutrient-enriched water with or without the mechanical support of an inert medium, such as sand or gravel," and in The World Book Encyclopedia, 1996 as "the science of growing plants without soil."

The most common aspect of all these definitions is that hydroponics means growing plants without soil, with the sources of nutrients either a nutrient solution or nutrient-enriched water, and that an inert mechanical root support (sand or gravel) may or may not be used. It is interesting to note that in only two of the six definitions is hydroponics defined as a "science."

Searching for definitions of hydroponics in various books and articles, the following were found. Devries (2003) defines hydroponic plant culture as "one in which all nutrients are supplied to the plant through the irrigation water, with the growing substrate being soilless (mostly inorganic), and that the plant is grown to produce flowers or fruits that are harvested for sale." In addition, Devries (2003) states, "hydroponics used to be considered a system where there was no growing media at all, such as the nutrient film technique in vegetables. But today it's accepted that a soilless growing medium is often used to support the plant root system physically and provide for a favorable buffer of solution around the root system." Resh (1995) defines hydroponics as "the science of growing plants without the use of soil, but by use of an inert medium, such as gravel, sand, peat, vermiculite, pumice, or sawdust, to which is added a nutrient solution containing all the essential elements needed by the plant for its normal growth and development." Wignarjah (1995) defines hydroponics as "the technique of growing plants without soil, in a liquid culture." In an American Vegetable Grower article entitled "Is hydroponics the answer?" (Anonymous, 1978), hydroponics was defined for the purpose of the article as "any method which uses a nutrient solution on vegetable plants, growing with or without artificial soil mediums." Harris (1977) suggested that a modern definition of hydroponics would be "the science of growing plants in a medium, other than soil, using mixtures of the essential plant nutrient elements dissolved in water." Jensen (1997) stated that hydroponics "is a technology for growing plants in nutrient solutions (water containing fertilizers) with or without the use of an artificial medium (sand, gravel, vermiculite, rockwool, perlite, peat moss, coir, or sawdust) to provide mechanical support." Jensen (1997) defined the growing of plants without media as "liquid hydroponics" and with media as "aggregate hydroponics." Another defining aspect of hydroponics is how the nutrient solution system functions, whether as an "open" system in which the nutrient solution is discarded after passing through the root mass or medium, or as a "closed" system in which the nutrient solution, after passing through the root mass or medium, is recovered for reuse.

Similarly related hydroponic terms are "aqua (water) culture," "hydroculture," "nutriculture," "soilless culture," "soilless agriculture," "tank farming," or "chemical culture." A hydroponicist is defined as one who practices hydroponics, and hydroponicum defined as a building or garden in which hydroponics is practiced.

Historical Past

The growing of plants in nutrient-rich water has been practiced for centuries. For example, the ancient Hanging Gardens of Babylon and the floating gardens of the Aztecs in Mexico were hydroponic in nature. In the 1800s, the basic concepts for the hydroponic growing of plants were established by those investigating how plants grow (Steiner, 1985). The soilless culture of plants was then popularized in the 1930s in a series of publications by a California scientist (Gericke, 1929, 1937, 1940).

During the Second World War, the U.S. Army established large hydroponic gardens on several islands in the western Pacific to supply fresh vegetables to troops operating in that area (Eastwood, 1947). Since the 1980s, the hydroponic technique has become of considerable commercial value for vegetable (Elliott, 1989) and flower (Fynn and Endres, 1994) production, and as of 1995 there are over 60,000 acres of greenhouse vegetables being grown hydroponically throughout the world, an acreage that is expected to continue to increase (Jensen, 1995). In a 2004 Hydroponic Merchants Association publication (see page v), they report over 55,000 acres of hydroponic greenhouse vegetable production worldwide, with about 1,000 acres in the United States, 2,100 acres in Canada, and 2,700 acres in Mexico. In these three countries, 68% of the production is in tomato, 15% in cucumber and 17% in pepper.

Hydroponics in Space

Hydroponics for space applications — providing a means of purifying water, maintaining a balance between oxygen (O2) and carbon dioxide (CO2) in space compartments, and supplying food for astronauts — is being intensively researched (Knight, 1989; Schwartzkopf, 1990; Tibbitts, 1991; Brooks, 1992). Hydroponic growing in desert areas of the world (Jensen and Tern, 1971) and in areas such as the polar regions (Tapia, 1985; Rogan and Finnemore, 1992; Sadler, 1995; Budenheim et al., 1995) or other inhospitable regions will become important for providing food and/or a mechanism for waste recycling (Budenheim, 1991, 1993).

Hydroponics/Soilless Culture

Actually, hydroponics is only one form of soilless culture. It refers to a technique in which plant roots are suspended in either a static, continuously aerated nutrient solution or a continuous flow or mist of nutrient solution. The growing of plants in an inorganic substance (such as sand, gravel, perlite, rockwool) or in an organic material (such as sphagnum peat moss, pine bark, or coconut fiber) and periodically watered with a nutrient solution should be referred to as soilless culture but not necessarily hydroponic. Some may argue with these definitions, as the common conception of hydroponics is that plants are grown without soil, with 16 of the 19 required essential elements (see pages 29-33) provided by means of a nutrient solution that periodically bathes the roots.

Most of the books on hydroponic/soilless culture (see References) focus on the general culture of plants and the design of the growing system, giving only sketchy details on the rooting bed design and the composition and management of the nutrient solution. Although the methods of solution delivery and plant support media may vary considerably among hydroponic/ soilless systems, most have proven to be workable, resulting in reasonably good plant growth. However, there is a significant difference between a "working system" and one that is commercially viable. Unfortunately, many workable soilless culture systems are not commercially sound. Most books on hydroponics would lead one to believe that hydroponic/soilless culture methods for plant growing are relatively free of problems since the rooting media and supply of nutrient elements can be controlled. Jensen (1997), in his overview, stated, "hydroponic culture is an inherently attractive, often oversimplified technology, which is far easier to promote than to sustain. Unfortunately, failures far outnumber the successes, due to management inexperience or lack of scientific and engineering support." Experience has shown that hydroponic/soilless growing requires careful attention to details and good growing skills. Most hydroponic/soilless growing systems are not easy to manage by the inexperienced and unskilled. Soil growing is more forgiving of errors made by the grower than are most hydroponic/soilless growing systems, particularly those that are purely hydroponic.

Advantages and Disadvantages

In 1981, Jensen listed the advantages and disadvantages of the hydroponic technique for crop production, many of which are still applicable today:

Advantages a. Crops can be grown where no suitable soil exists or where the soil is contaminated with disease.

  1. Labor for tilling, cultivating, fumigating, watering, and other traditional practices is largely eliminated.
  2. Maximum yields are possible, making the system economically feasible in high-density and expensive land areas.
  3. Conservation of water and nutrients is a feature of all systems. This can lead to a reduction in pollution of land and streams because valuable chemicals need not be lost.
  4. Soilborne plant diseases are more readily eradicated in closed systems, which can be totally flooded with an eradicant.
  5. More complete control of the environment is generally a feature of the system (i.e., root environment, timely nutrient feeding or irrigation), and in greenhouse-type operations, the light, temperature, humidity, and composition of the air can be manipulated.
  6. Water carrying high soluble salts may be used if done with extreme care. If the soluble salt concentrations in the water supply are over 500 ppm, an open system of hydroponics may be used if care is given to frequent leaching of the growing medium to reduce the salt accumulations.
  7. The amateur horticulturist can adapt a hydroponic system to home and patio-type gardens, even in high-rise buildings. A hydroponic system can be clean, lightweight, and mechanized.

Disadvantages a. The original construction cost per acre is great.

  1. Trained personnel must direct the growing operation. Knowledge of how plants grow and of the principles of nutrition is important.
  2. Introduced soilborne diseases and nematodes may be spread quickly to all beds on the same nutrient tank of a closed system.
  3. Most available plant varieties adapted to controlled growing conditions will require research and development.
  4. The reaction of the plant to good or poor nutrition is unbelievably fast. The grower must observe the plants every day.

Wignarajah (1995) gave the following advantages of hydroponics over soil growing:

  1. All of the nutrients supplied are readily available to the plant.
  2. Lower concentrations of the nutrient can be used.
  3. The pH of the nutrient solution can be controlled to ensure optimal nutrient uptake.
  4. There are no losses of nutrients due to leaching.

Wignarajah (1995) gave only one disadvantage of hydroponic systems, "that any decline in the O2 tension of the nutrient solution can create an anoxic condition which inhibits ion uptake." His recommendation is that only aeroponics solves this problem since it provides a "ready supply of O2 to the roots, hence never becomes anoxic."

The Hydroponic Techniques

In 1983, Collins and Jensen prepared an overview of the hydroponic technique of plant production, and more recently, Jensen (1995) discussed probable future hydroponic developments, stating that "the future growth of controlled environment agriculture will depend on the development of production systems that are competitive in terms of costs and returns with open field agriculture" and that "the future of hydroponics appears more positive today than any time over the last 30 years." In a brief review of hydroponic growing activities in Australia, Canada, England, France, and Holland, Brooke (l995a) stated that "today's hydroponic farmer can grow crops safely and in places that were formerly considered too barren to cultivate, such as deserts, the Arctic, and even in space." He concluded, "hydroponic technology spans the globe." Those looking for a brief overview of the common systems of hydroponic growing in use today will find the article by Rorabaugh (1995) helpful.

Proper instruction in the design and workings of a hydroponic/soilless culture system is absolutely essential. Those not familiar with the potential hazards associated with these systems or who fail to understand the chemistry of the nutrient solution required for their proper management and plant nutrition will normally fail to achieve commercial success with most hydro-ponic/soilless culture systems.

The technology associated with plant production, hydroponic or otherwise, is rapidly changing, as can be evaluated by reviewing the various bibliographies on hydroponics (Anon., 1984; Gilbert, 1979, 1983, 1984, 1985, 1987, 1992). Those interested in hydroponics must keep abreast of the rapid developments that are occurring by subscribing to and reading periodicals, such as the magazines The Growing Edge;1 and Maximum Yield Hydrogardening2 by membership and participation in groups devoted to the hydroponic/soilless growing of plants; and by becoming acquainted with the books, bulletins, and developing computer, video, and Internet (i.e., e-mail: hydrosoc-[email protected]) sources of hydroponics information. It could be that the problem today is not the lack of information on hydroponics (there are over 400,000 Web sites about hydroponics, for example), but the flood of information, much lacking a scientific basis, that leads to confusion and poor decision-making on the part of users.

"Is Hydroponics the Answer?" was the title of an article that appeared in 1978 (Anon., 1978) that contained remarks by those prominent at that time in discussions of hydroponic topics. In the article was the following quote: "Hydroponics is curiously slow to receive the mass grower endorsement that some envisioned at one time." Carruthers (1998) provided a possible answer for what has been occurring in the United States, stating, "the reasons for this slow growth can be attributed to many factors, including an abundance of rich, fertile soil and plenty of clean water." At the 1985 Hydroponics Worldwide: State of the Art in Soilless Crop Production conference, Savage (1985a) in his review stated, "many extravagant claims have been made for hydroponics/ soilless systems, and many promises have been made too soon, but the reality is that a skilled grower can achieve wondrous results." In addition, he sees "soilless culture technology as having reached 'adulthood' and rapid maturing to follow." In addition, Savage (1985a) stated that "soilless and controlled environment crop production take special skills and training; however, most failures were not the result of the growing method, but can be attributed to

1 The Growing Edge, P.O. Box 1027, Portland, OR 97339; tel: (503) 757-0027; Web site:

2 Maximum Yield Hydro Gardening, 11-1925 Bowden Rd., Nanaimo, B.C. Canada V95 1H1; tel: (250) 729-2677; fax: (205) 729-2687; Website:

poor financial planning, management, and marketing." More recently, at the 2003 South Pacific Soilless Culture Conference, Alexander (2003b) reported on current developments, stating "hydroponics is growing rapidly everywhere and within the next 5 to 10 years will be established as a major part of our agricultural and horticultural production industries."

Wilcox (1980) wrote about the "High Hopes of Hydroponics," stating that the "future success in the greenhouse industry will demand least-cost, multiple-cropping production strategies nearer to the major population centers." More recently, Naegely (1997) stated that the "greenhouse vegetable business is booming." She concluded, "the next several years promise to be a dynamic time in the greenhouse vegetable industry." Growth in the hydroponic-greenhouse industry was considerable in the 1990s, and its continued future expansion will depend on developments that will keep "controlled environmental agriculture" (CEA) systems financially profitable (see pages 305-307). Jensen (1997) remarked, "while hydroponics and CEA are not synonymous, CEA usually accompanies hydroponics — their potentials and problems are inextricable."

"Hydroponics for the New Millennium: A Special Section on the Future of the Hydroponic Industry" is the title of a series of articles by six contributors who addressed this topic from their own perspectives; the final comment was, "it really is an exciting time to be in the worldwide hydroponic industry, whether it's for commercial production or a hobby" [Growing Edge 11(3):6-l3, 2000]. Jones and Gibson (2002) stated that "the future of the continued expansion of hydroponics for the commercial production of plants is not encouraging unless a major breakthrough occurs in the way the technique is designed and used." Those factors limiting wide application are cost, the requirement for reliable electrical power, inefficiencies in the use of water and nutrient elements, and environmental requirements for disposal of spent nutrient solution and growing media. Just recently, Schmitz (2004) remarked that "hydroponics is also seen as too technical, too expensive, too everything."

The Future of Hydroponics

What is not encouraging for the future is the lack of input from scientists in public agricultural colleges and experiment stations that at one time made significant contributions to crop production procedures, including hydroponics. The early hydroponic researchers, Dr. W.F. Gericke and D.R. Hoagland for example, were faculty members at the University of California. Today, there are only a few in universities who are still active in hydroponic investigations and research. The current status of Agricultural Cooperative Extension programs varies considerably from state to state. In the past, state specialists and county agents played major roles as sources for reliable information, but today these services are being cut back. Also, few of these specialists and agents have any expertise in hydroponics or extensive experience in dealing with greenhouse management questions. Edwards (1999), however, sees a positive role that county extension offices play, providing assistance to those seeking information, stating that "the Extension office is often the first place these people contact."

The science of hydroponics is currently little investigated, and much of the current focus is on the application of existing hydroponic techniques. Hydroponics, as a method of growing, is being primarily supported by those in the private sector who have a vested interest in its economic development. An example is the Hydroponic Merchants Association (HMA),1 an association of those who manufacture, distribute, and market hydroponic growing systems that "exists to serve the interests of those who have made hydroponics, aquaponics, greenhouse growing, and other associated trades their livelihood" (Peckenpaugh, 2002f). Most of the hydroponic scientific advancements made today are by those who are investigating how this technique can be made to work for plant production in outer space (Hankinson, 2000a).

Another disturbing factor is that the Hydroponic Society of America2 has not been active since 1997 when it published its last Proceedings. The Society was founded in 1979 and had been holding annual meetings and publishing proceedings from 1981 through 1997. Also, the International Society of Soilless Culture,3 an organization that had held meetings and published proceedings in the past, has not been active for several years.

The role that commercial and scientific advancements have on society cannot be ignored when considering what is occurring in hydroponics today. The ease of movement of produce by surface and air transport, for example, allows for the growing of food products at great distances from their point of consumption. The advent of plastics has had a enormous impact on hydroponics because growing vessels, liquid storage tanks, drip irrigation tubing and fittings, greenhouse glazing materials, and sheeting materials, essential components in all hydroponic/greenhouse operations, are derived from a wide range of plastic materials that vary in their physical and chemical characteristics (Garnaud, 1985; Wittwer, 1993). The use of computers and computer control of practically every aspect of a hydroponic/greenhouse operation have revolutionized decision-making and managerial control procedures. Although one might conclude that hydroponic crop production is becoming more and more a science, there is still much art required that makes this method of plant production a challenge as well as an adventure.

The role of the Internet, the superhighway of information technology and communication, has changed and will continue to change how we educate ourselves and obtain the information and devices needed to establish and manage hydroponic/greenhouse systems. The ability to instantly send word and picture messages opens to the most isolated the world of information and resources added to the Internet daily. A grower with a plant problem,

1 Hydroponic Merchants Association, 10210 Leatherland Court, Manassas, VA 20111; tel: (703) 392-5890; fax: (503) 257-0213;

2 Hydroponic Society of America, P.O. Box 1183, El Centro, CA 94530; tel: (510) 232-2323; fax: (510) 232-2384; Web site:

3 International Society of Soilless Culture. (There is no current address for the Society and the Web site is not currently being supported.)

whether cultural or nutritional, the result of a disease or insect, can send photographs to an expert for identification and solution. The Internet is "awash" with innumerable Web sites on practically any subject. What might prove to be the challenge is how to separate the reliable from the unreliable while wading through the mass of material that exists.

This book describes various systems of hydroponic/soilless growing and the requirements essential for success. The common procedures for both inorganic and organic media as well as purely hydroponic culture are included, with emphasis on the essential requirements for each technique. Although the importance of these factors is discussed in some detail in this text, the reader is advised to seek other resources for general information on plant production, greenhouse design and construction, environmental control, cultivar selection, general plant cultural practices, and pest management.

Elemental Compound and Ion Symbol Designation

In this text, all elements are designated by their symbols, whereas reagents and compounds are named and their symbol compositions shown when first mentioned in that portion of the text. The symbols for those elements, compounds, and ions found in this text are as follows:
























Fe Pb Li

Mg Mn Mo



















Y Zn













Carbon dioxide






Dihydrogen phosphate


Monohydrogen phosphate






Phosphate (ortho)








In those situations where there may be confusion if only the symbol is used, both the element, compound, or ion and its symbol will be used.

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