Hydroponic growing is a method of growing plants without the use of soil. To replace the nutrients that are found in the soil, a nutrient solution is applied to the roots of the growing plants. How the nutrients are applied to the plants determines what kind of hydroponic system is used.
Water Culture Systems
Water culture systems provide a constant supply of nutrient solution to the roots of the plants. Water culture systems include the film technique, which supplies a trickle stream of solution along the roots of the plant by placing the plant in a trough and pouring the liquid down on it. Aeroponics is another technique where plants are suspended in a container and the roots are misted with a nutrient solution from a spray gun. The aeration method uses a a pump inside the nutrient solution to bubble it up, touching the plant roots.
Aggregate systems use a inert growing medium such as perlite, vermiculite, rockwool or gravel to support the plant root system, according to the Virginia Cooperative Extension. The flood and drain method is a system where plants are put into a growing medium, inside a container, then placed into another water-holding container that floods and drains nutrient solution at regular intervals. The trickle feed method pumps nutrient solution from a reservoir to a series of small tubes which supply containers with plants. The tube culture is a modification of this: a plastic tube or bag, filled with a light weight growing medium with holes punched in the sides for plants, is supplied a trickle of solution from a reservoir.
Passive and Active Systems
Passive systems use a growing media or a wick to provide the nutrient solution to the plants, and they are best utilized for growing seeds and cuttings. Active systems use pumps or other devices to supply nutrient solution to the plants.