Hydroponic gardening, or gardening without soil, has been practiced since ancient times. The Babylonians, Egyptians and Aztecs employed the technique in areas where soil was nutrient-deficient. In the 13th century, Marco Polo described the lush, luxurious water gardens of China. Plants grown without soil require the same nutrients that their soil-bound cousins utilize, but the delivery of those elements offers unique challenges.
The major nutrients, or macroelements, are oxygen, carbon, hydrogen, nitrogen, phosphorus, potassium, calcium, magnesium and sulfur. Carbon is not an issue in traditional, outdoor gardens. In a greenhouse, however, where most hydroponic plants are grown, this element must be considered.
Oxygen, usually abundant in well-aerated soil, is also of concern to a hydroponic grower. Air bubbles may be added to the nutrient solution to aid in oxygen delivery. All other macroelements are likely to be found in commercial fertilizers.
Microelements are needed in minuscule quantities. These consist of iron, zinc, manganese, copper, boron, molybdenum and chlorine. The importance of other elements, such as selenium, is still debated among experts.
Without proper amounts of both light and warmth, these nutrients will not be fully exploited. Most plants require eight to 10 hours of sunlight and a temperature of between 50 and 80 degrees, depending upon the crop. Artificial light is usually needed in indoor settings. Care must be taken to ensure that the heat generated by artificial lights does not raise the temperature beyond a crop's tolerance range.
The symptoms of nutrient scarcity are similar for both soil-grown and hydroponic plants. A deficiency in the macroelements, for example, will often cause leaves to discolor and die. A lack of any of the microelements may precipitate mottling or puckering in the plant. Leaf-burn is sometimes present, along with wilting or a tendency toward "cupping," in which the leaves take on the shape of a cup.
Plants should be scrutinized often for signs of deficiency. Since many symptoms are common to different conditions, it is important to test the affected plant as well as the nutrient solution. Tests may be conducted by your state's department of agriculture.
Most common fertilizers do not contain all elements required for hydroponic use. A product designed specifically for soil-free gardens is crucial. Pre-mixed formulas are available at garden centers or over the Internet. For specific nutritional deficiencies, foliar sprays may be applied directly to leaves. These sprays offer a fast boost for nutrient-starved plants.
Those with sufficient expertise may mix their own hydroponic fertilizers, but local water quality must be taken into account. Contact your local university or your county's agricultural service for advice on creating a suitable hydroponic solution.
A carbon generator is advised for large, indoor hydroponics operations. Carbon dioxide is rapidly depleted in enclosed greenhouses. A carbon generator is attached to a sensor. It adds carbon dioxide to the atmosphere whenever the amount drops below optimum levels.
Never use nutrient solutions for more than two weeks. If salt is allowed to build up in solutions, plant production will diminish.
Check the water periodically for unwanted chemicals, to ensure that nothing interferes with the uptake of nutrients.