The term "hydroponics" refers to any of several techniques for growing plants without soil. Plants need nutrients, and nutrients are dissolved in water. Traditionally grown plants get their nutrients from the water held in soil, but the soil itself is not necessary. The use of hydroponics allows the grower to more closely regulate the nutrients, allows for more plants in less space, and since the water is recirculated, it requires much less water than conventional growing methods. The simplest method is passive hydroponics. This method places the plant in a container of inert material such as gravel, coir fiber, or vermiculite. The container is then placed in a tray of water with nutrients added. The large spaces between particles of growing medium allow nutrients to be moved to the plant roots by capillary action. This system needs to be washed regularly to prevent the buildup of salts. Ebb and flow hydroponics involves an upper tray which contains the plant and an inert medium and a lower tray which contains nutrient solution. Using a timer, the solution is pumped at regular intervals into the upper tray and allowed to drain back into the lower tray. This provides constant aeration, which is necessary for the roots to thrive. Deep water cultivation or raft cultivation means that a cover is suspended over the nutrient solution, holes are made in the cover, and the plants are inserted with their roots hanging directly in the nutrient solution. A pump is necessary to keep the water aerated, and the reservoir must be light proof to prevent the growth of algae. | 
