The cultivation of plants without the use of soil is called hydroponics. Plants in traditional gardens receive water and nutrients from the soil they live in; in hydroponic gardening, plants receive all their nutritional needs from a nutrient solution that their roots sit in or are sprayed by.
For a hydroponic system to work, plants require many of the same factors as those grown in soil. Plants need nutrients, water, light and air. Water and nutrients are provided by the nutrient solution, but light may need to be replaced when the hydroponic system is indoors. The Virginia Cooperative Extension recommends metal halide, sodium vapor lights, grow-lights or fluorescent lights paired with an incandescent light to provide the correct light requirements for a plant. A fan may be required to circulate air throughout the room for the purpose of pollination and to prevent disease.
The nutrient solution provides the plants all 13 elements required for the healthy growth of a plant. Hydroponic solutions, according to the Alabama Cooperative Extension, are available from gardening catalogs, garden centers, fertilizer companies and hydroponics specialty stores. Premixed solutions are available, but nutrients are also available individually for mixing. After mixing a nutrient solution, the pH requires testing. A good hydroponic solution should be between 5.5 and 6.5 on the pH scale.
Water culture systems use a constant stream of nutrient solution, or the spraying of nutrient solution onto bare, unsupported plant roots that hang loose. Nutrient film runs a steady stream of nutrients over the plant roots to keep them moist and provide nutrients. An aeroponic system uses spraying heads to mist plants that are suspended in a container that exposes the plant roots. Plants are suspended above a reservoir of nutrient solution. A the bottom of the reservoir sits an air pump that sends bubbles up through the solution. As the bubbles burst at the solution's surface, a small amount of the solution is sprayed onto the plant roots.
Aggregate systems use a growing medium or inert material such as perlite, rock wool, vermiculite, sand or foam chips to contain the roots of the plants in the hydroponic system. Nutrient solution is flooded into the growing medium, or substrate, which briefly holds the nutrient solution to the plant roots. Common aggregate systems are the trickle feed method, flood and drain method, and the tube culture.
As a nutrient solution evaporates, deficiencies in certain nutrients may affect plant growth. Green plants with yellowing leaves at the bottom that continue to fall off are likely suffering from a lack of nitrogen. When a plant turns bluish-green with yellowing lower leaves, the plant is likely missing phosphorous. To quickly fix a nutrient deficiency, foliar fertilizer should be sprayed onto the plant. To prevent the problem, change the nutrient solution every week or every two weeks to keep it fresh.