Hydroponics (from the Greek words hydro water and ponos labor) is a method of growing plants using mineral nutrient solutions, without soil. Terrestrial plants may be grown with their roots in the mineral nutrient solution only or in an inert medium, such as perlite, gravel, coco, hydroton, rockwool and many more.

Plant physiology researchers discovered in the 19th century that plants absorb essential mineral nutrients as inorganic ions in water. In natural conditions, soil acts as a mineral nutrient reservoir but the soil itself is not essential to plant growth. When the mineral nutrients in the soil dissolve in water, plant roots are able to absorb them. When the required mineral nutrients are introduced into a plant's water supply artificially, soil is no longer required for the plant to thrive. Almost any terrestrial plant will grow with hydroponics. Hydroponics is also a standard technique in biology research and teaching.

The study of crop nutrition began thousands of years ago. Ancient history tells us that various experiments were undertaken by Theophrastus (372-287 B.C.), while several writings of Dioscorides on botany dating from the first century A.D., are still in existence..The earliest published work on growing terrestrial plants without soil was the 1627 book, Sylva Sylvarum by Sir Francis Bacon, printed a year after his death. Water culture became a popular research technique after that. In 1699, John Woodward published his water culture experiments withspearmint. He found that plants in less pure water sources grew better than plants in distilled water. By 1842 a list of nine elements believed to be essential to plant growth had been made out, and the discoveries of the German botanists,Julius von Sachs and Wilhelm Knop, in the years 1859-65, resulted in a development of the technique of soilless cultivation..Growth of terrestrial plants without soil in mineral nutrient solutions was called solution culture. It quickly became a standard research and teaching technique and is still widely used today. Solution culture is now considered a type of hydroponics where there is no inert medium.

In 1929, Professor William Frederick Gericke of the University of California at Berkeley began publicly promoting that solution culture be used for agricultural crop production. He first termed it aquaculture but later found that aquaculture was already applied to culture of aquatic organisms. Gericke created a sensation by growing tomato vines twenty-five feet high in his back yard in mineral nutrient solutions rather than soil. By analogy with the ancient Greek term for agriculture, geoponics, the science of cultivating the earth, Gericke introduced the term hydroponics in 1937 (although he asserts that the term was suggested by Dr. W. A. Setchell, of the University of California) for the culture of plants in water (from the Greek hydros, "water", and ponos, "labor"). Reports of Gericke's work and his claims that hydroponics would revolutionize plant agriculture prompted a huge number of requests for further information. Gericke refused to reveal his secrets claiming he had done the work at home on his own time. This refusal eventually resulted in his leaving the University of California. In 1940, he wrote the book, Complete Guide to Soilless Gardening.

Two other plant nutritionists at the University of California were asked to research Gericke's claims. Dennis R. Hoaglang and Daniel I. Arnon wrote a classic 1938 agricultural bulletin, The Water Culture Method for Growing Plants Without Soil, debunking the exaggerated claims made about hydroponics. Hoagland and Arnon found that hydroponic crop yields were no better than crop yields with good quality soils. Crop yields were ultimately limited by factors other than mineral nutrients, especially light. This research, however, overlooked the fact that hydroponics has other advantages 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 as they need. This is important as one of the most common errors when growing is over- and under- watering; and hydroponics prevents this from occurring as large amounts of water can be made available to the plant and any water not used, drained away, recirculated, or actively aerated, eliminating anoxic conditions which drown root systems in soil. 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 not be able to access oxygen; too little and the plant will lose the ability to transport nutrients, which are typically moved into the roots while in solution. These two researchers developed several formulas for mineral nutrient solutions, known as Hoagland solutions. Modified Hoagland solutions are still used today.

One of the early 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.

In the 1960s, Allen Cooper of England developed the Nutrient Film Technique. 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 their Controlled Ecological Life Support System or CELSS. Hydroponics intended to take place on Mars are using LED lighting to grow in different color spectrum with much less heat. In 1978, hydroponics pioneer Dr. Howard Resh published the first edition of his book "Hydroponics Food Production." This book (now updated) spurred what has become known as the 3-part base nutrients formula that is still a major component of today's hydroponics gardening. Resh later went on to publish other books, and is currently in charge of a highly advanced hydroponics research and production facility in the Caribbean.

Today, hydroponics is an established branch of agronomical science. Progress has been rapid, and results obtained in various countries have proved it to be thoroughly practical and to have very definite advantages over conventional methods of horticulture. The two chief merits of the soilless cultivation of plants are, first, much higher crop yields, and secondly, the fact that hydroponics can be used in places where ordinary agriculture or gardening is impossible. Thus not only is it a profitable undertaking, but one which has proved of great benefit to humanity. People living in crowded city streets, without gardens, can grow fresh vegetables and fruits in window-boxes or on house tops. By means of hydroponics all such places can be made to yield a regular and abundant supply of clean, health-giving greenstuff. Not only town dwellers, but also country residents have cause to be thankful to soiless culture. Deserts, rocky and stony land in mountainous districts or barren and sterile areas can be made productive.

Other advantages include faster growth combined with relative freedom from soil diseases, and very consistent crops, the quality of produce being excellent. There is also a considerable reduction in growing area, weeds are practically non-existent, while standard methods and automatic operations mean less labor, less cost, and no hard manual work. Some plants can be raised, out of season, better control of crops naturally results in addition to no dirt and no smells. Waterlogging never occurs now. Chemically grown plants are not inferior to naturally reared ones in point of flavor, nor have analyses shown any deficiency in vitamin content.

The two main types of hydroponics are solution culture and medium culture. Solution culture does not use a solid medium for the roots, just the nutrient solution. The three main types of solution culture are static solution culture, continuous flow solution culture and aeroponics. The medium culture method has a solid medium for the roots and is named for the type of medium, e.g. sand culture, gravel culture or rockwool culture. There are two main variations for each medium, subirrigation and top irrigation. 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 growth in the nutrient solution.

With pest problems reduced, and nutrients constantly fed to the roots, productivity in hydroponics is high, plant growth being limited by the low levels of carbon dioxide in the atmosphere, or limited light. To increase yield further, some sealed greenhouses inject carbon dioxide into their environment to help growth (CO2 enrichment), or add lights to lengthen the day, control vegetative growth etc.

Organic horticulture is the science and art of growing fruits, vegetables, flowers, or ornamental plants by following the essential principles of organic agriculture in soil building and conservation, pest management, and heirloom variety preservation.

The Latin words hortus (garden plant) and cultura (culture) together form horticulture, classically defined as the culture or growing of garden plants. Horticulture is also sometimes defined simply as “agriculture minus the plough.” Instead of the plough, horticulture makes use of human labour and gardener’s hand tools, although small small machine tools like rotary tillers are common now.

Vermicompost, Mulches, cover crops, compost, manures, and mineral supplements are soil-building mainstays that distinguish this type of farming from its commercial counterpart. Through attention to good healthy soil condition,it is expected that insect, fungal, or other problems that sometimes plague plants can be minimized. However, pheromone traps, insecticidal soap sprays, and other pest-control methods available to organic farmersare also sometimes utilized by organic horticulturists.

Horticulture involves five areas of study. These areas are floriculture (includes production and marketing of floral crops), landscape horticulture (includes production, marketing and maintenance of landscape plants), olericulture (includes production and marketing of vegetables), pomology (includes production and marketing of fruits), and postharvest physiology (involves maintaining quality and preventing spoilage of horticultural crops). All of these can be, and sometimes are, pursued according to the principles of organic cultivation.

Organic horticulture (or organic gardening) is based on knowledge and techniques gathered over thousands of years. In general terms, organic horticulture involves natural processes, often taking place over extended periods of time, and a sustainable, holistic approach - while chemical-based horticulture focuses on immediate, isolated effects and reductionist strategies.

There are a number of formal organic gardening and farming systems that prescribe specific techniques. They tend to be more specific than, and fit within, general organic standards. Biodynamic farming is an approach based on the esoteric teachings of Rudolf Steiner. The Japanese farmer and writer Masanobu Fukuoka invented a no-till system for small-scale grain production that he called Natural Farming. French intensive and biointensive methods and SPIN Farming (Small Plot INtensive) are all small scale gardening techniques.

A garden is more than just a means of providing food, it is a model of what is possible in a community - everyone could have a garden of some kind (container, growing box, raised bed) and produce healthy, nutritious organic food, a farmers market, a place to pass on gardening experience, and a sharing of bounty, promoting a more sustainable way of living that would encourage their local economy. A simple 4' x 8' (32 square feet) raised bed garden based on the principles of bio-intensive planting and square foot gardening uses fewer nutrients and less water, and could keep a family, or community, supplied with an abundance of healthy, nutritious organic greens, while promoting a more sustainable way of living.

Other methods can also be used to supplement an existing garden. Methods such as composting, or vermicomposting. These practices are ways of recycling organic matter into some of the best organic fertilizers and soil conditioner. Vermicompost is especially easy. The byproduct is also an excellent source of nutrients for an organic garden.

Differing approaches to pest control are equally notable. In chemical horticulture, a specific insecticide may be applied to quickly kill off a particular insect pest. Chemical controls can dramatically reduce pest populations in the short term, yet by unavoidably killing (or starving) natural control insects and animals, cause an increase in the pest population in the long term, thereby creating an ever increasing problem. Repeated use of insecticides and herbicides also encourages rapid natural selection of resistant insects, plants and other organisms, necessitating increased use, or requiring new, more powerful controls.

In contrast, organic horticulture tends to tolerate some pest populations while taking the long view. Organic pest control requires a thorough understanding of pest life cycles and interactions, and involves the cumulative effect of many techniques, including:
• Allowing for an acceptable level of pest damage
• Encouraging predatory beneficial insects to flourish and eat pests
• Encouraging beneficial microorganisms
• Careful plant selection, choosing disease-resistant varieties
• Planting companion crops that discourage or divert pests
• Using row covers to protect crop plants during pest migration periods
• Rotating crops to different locations from year to year to interrupt pest reproduction cycles
• Using insect traps to monitor and control insect populations

Each of these techniques also provides other benefits, such as soil protection and improvement, fertilization, pollination, water conservation and season extension. These benefits are both complementary and cumulative in overall effect on site health. Organic pest control and biological pest control can be used as part of integrated pest management (IPM). However, IPM can include the use of chemical pesticides that are not part of organic or biological techniques.