Hydroponics is a method of cultivating plants without soil. Instead of being grown in soil, the plants are grown in a chemical solution that contains all the nutrients essential for plant growth. Nearly all kinds of plants can be raised by this method, and usually they are at least as healthy and productive as plants grown in rich, fertile soil. Like those grown in soil, plants cultivated by hydroponics require a suitable temperature and an adequate amount of sunlight and air. In popular usage, hydroponics is known by a variety of other terms, including soilless gardening, water culture, tank farming, and chemical gardening.
For many years, plant scientists have been using hydroponics to grow experimental plants. This method of plant growing has also become a popular hobby. In recent years the techniques of hydroponics have been enough improved and developed to make possible large-scale crop raising. However, because hydroponic agriculture requires expensive equipment and skilled labor, its uses are limited.
In the United States and Canada hydroponic agriculture is used chiefly
to raise vegetables and flowers out of season in greenhouses. Usually
the greenhouses are in well-populated areas, where the demand for the
produce makes hydroponic gardening profitable. Hydroponics is also
successfully practiced in tropical areas with thin or poor soils, such
as coral and volcanic islands in the Atlantic and Pacific oceans. For
example, in the Bahamas hydroponic gardening is used to grow vegetables
to supply tourists.
During World War II the U.S. Army operated experimental hydroponic farms on various islands in the Pacific Ocean. Several years later, during the Korean War, hydroponic gardens in Japan supplied American troops with fresh vegetables.
Methods of Cultivation
There are two basic methods of growing plants by hydroponics: water culture and sand or gravel culture. In the water culture method the roots of the plants are directly immersed in the nutrient solution. In the sand or gravel culture method the plants are rooted in a material, such as sand or gravel, through which the nutrient solution is pumped.
In the water culture method, plant sprouts are set in a porous material, such as wood shavings or peat moss, which is spread over a net of fine chicken wire. The wire netting is suspended one or more inches above a nutrient solution that is in a shallow tank. As the sprouts develop, the roots grow down through the underside of the net into the solution. Sometimes the wire netting does not supply enough support for the plants, especially if, like tomatoes, they are tall. In such cases a wire frame is necessary for additional support.
Because plant roots need air for normal growth, a method of aerating the nutrient solution must be provided. Air may be bubbled through the solution from a pipe at the bottom of the tank, or it may be released from a valve and mixed into the solution as it is pumped into the tank. The space between the solution and the wire netting also helps provide the air required by the plant roots.
Some water culture tanks are very small, but for commercial operations they may be as large as 100 feet long, 4 feet wide, and 8 inches deep. The tanks are made of wood, concrete, or sheet metal.
Sand or Gravel Culture
In this method of culture the plants are grown in shallow tanks that are similar to those used in water culture. These tanks are filled with a chemically inactive, porous material in which the plants can take root. Coarse pure sand, fine gravel, crushed rock, and cinders are among the materials most commonly used. At various times the nutrient solution is poured or pumped into the tank and is allowed to seep through the porous material. It then drains off into a reservoir tank. The frequency of pumping depends on a variety of factors. These include the size of the plants, the intensity of light, and the temperature.
Sand or gravel culture has several advantages over water culture. The plants do not need frames for support, because the roots become firmly embedded in the sand or gravel. In addition, the porous supporting material allows the plant roots to receive air naturally, eliminating the need to aerate the nutrient solution. Because of its advantages, sand or gravel culture is the technique most often used for commercial hydroponics.
Most plants can thrive in any of a wide variety of solutions. However, every solution must provide all the elements essential to green plants. Six of the elements, calcium, magnesium, potassium, nitrogen, sulfur, and phosphorus, are needed in relatively large amounts, and they are called primary elements. Very small quantities of boron, iron, manganese, chlorine, copper, zinc, and molybdenum are also needed, and they are called trace elements. In addition, plants require three other primary elements: carbon, oxygen, and hydrogen. These elements can be obtained from the air or from water absorbed by the plants, and they do not have to be added to the nutrient solution.