Passive

• Perhaps the simplest of all methods is the passive hydroponic system. A passive system is where the plants sit in a nutrient solution. A plant is placed in a pot with some type of soil-free growing medium such as vermiculite or perlite. This medium allows air spaces around the root system. The pots have holes in the bottom of them to allow the roots access to the liquid. The roots then soak up the nutrients through capillary action. Capillary action is a physical property in which a liquid is "wicked" up through a string like substance. In this case the roots of the plant pull the liquid nutrients into the plant. The pots are placed inside a sealed tray that contains the liquid nutrients. When the level of the tray lowers more liquid is added. This particular method is used for fast growing plants such as lettuces and greens.
  
  

Ebb and Flow

• The plants are placed, in much the same fashion as the passive system, in a sealed tray. In the ebb and flow method there is a drain hole placed at either end of the plant tray. A nutrient tank or reservoir is located underneath the plant tray. A pump is switched on by a timer and then fills the plant tray. The liquid is allowed to fill the plant tray until it reaches a predetermined level. The pump is then shut off. The liquid nutrient then slowly drains back down into the reservoir below. This action mixes the solution and also aerates the roots for needed oxygen in between the nutrient pumping.
  
  

Deep Water Culture

• Deep-water culture is where the plant is floated on top of a water tank much like an aquarium. The plants are placed in small pots again filled with some type of growing medium to allow air and capillary action to draw the nutrients into the plant. The pots contain holes in the bottom which allow the roots of the plants to fill the deep-water tank. A small air pump, much like an air bubbler in an aquarium, feeds oxygen into the water. The plants take up both the nutrient and the oxygen provided by the small air pump. The tank must be devoid of any light, as algae may begin to grow in the nutrient rich liquid. More liquid nutrient is added as needed.