Hydroponics is a method of growing plants without soil. Instead, plants are grown in a liquid fertilizer that provides all the plants' nutrients. Basic hydroponic systems provide support for the roots, oxygen and carbon dioxide exchange, water and nutrients to the plant. Water culture systems do this without holding the plant in a substrate (a growing medium such as perlite), while aggregate systems do.
Nutrient Film Technique
The nutrient film technique is a water culture system. Plants are placed in a plastic trough or tube that has a constant stream of nutrient solution running through it. The trough is often sloped so that the film travels downward into a reservoir that pumps the nutrient solution back to the top of the system.
Aeroponics is a water culture system. A misting device sprays the plant roots with a nutrient solution. Plants are commonly suspended in a triangle planting structure that holds the stem of the plant while exposing the roots. Misting devices are placed inside the A-frame and spray the roots on a regular basis.
Aeration is a water culture method. Plants are suspended just above a reservoir of nutrient solution. An air pump, placed at the bottom of the reservoir, bubbles air through the solution. As the bubbles pop, nutrient solution touches the roots of the plant.
Flood and Drain Method
The flood and drain method is an aggregate system. Aggregate systems use an inert material such as gravel, clay pebbles or vermiculite to hold the plant roots in one place. The flood and drain method has plants suspended in this manner in a water holding container. The container floods and drains, wetting the roots and holding material. The roots are submerged in the solution for no more than 20 to 30 minutes, according to the Virginia Cooperative Extension.
Trickle Feed Method
The trickle feed method is an aggregate system. A 1/2-inch irrigation tube sits in a reservoir and pumps nutrient solution up into 1/8-inch tubes. The 1/8-inch tubes connect to an individual container and provide nutrient solution to the inert material and the plant roots.