A hydroponic growing system works by saturating a plant's roots with a nutrient-rich water solution. Because the solution carries everything a plant needs to grow and thrive, soil is unnecessary. Hydroponic growing systems also use some type of neutral medium, a material that supports the plant's roots.
The deepwater culture or reservoir method is the simplest type of hydroponic growing system. In this system, a reservoir holds the nutrient-rich solution, and the plants' roots dangle down into it. An air stone or similar device constantly aerates the solution, supplying the roots with oxygen and preventing the growth of algae or anaerobic microbes. The grower must change the solution periodically, as the plants eventually use up the nutrients suspended in the solution.
More complex hydroponic growing systems include the nutrient film technique and the ebb-and-flow method. In the nutrient film technique, plants are placed in single file within a gently sloping container. Pumps then continually pass nutrient solution over the roots. Because the roots are not submerged in a nutrient film system, aeration is not required.
Ebb-and-flow hydroponic systems use a pump that periodically fills and drains a plant's container with nutrient solution. These systems are costly and complex, and they are only necessary for plants that require set cycles of dry and wet conditions.