Named after the Greek words for water and labor, hydroponics is a range of soil-free growing systems that supply plants with nutrients dissolved in water. Plants naturally absorb nutrients in solution in soil, but hydroponics delivers calculated amounts of nutrients and removes the need for soil as a growing medium. The required water level in hydroponics differs according to the type of system, which includes floating raft, wick, drip, nutrient film technique and ebb and flow.
Floating Raft System
Also called water culture, floating raft hydroponics supports plants so that their roots are partially submerged in water. Plants grow in pockets in a styrofoam tray that floats on a nutrient solution. Plant roots require air as well as nutrients, so a pump circulates air through the solution, and only the lower portion of plant roots touch it. The solution should be deep enough to contain and supply nutrients to the lower plant roots. For example, lettuce plants in 3-inch-deep pots should have no more than 1/16 inch at the bottom of their pots protruding into a nutrient solution about 5 inches deep. Providing a gap between the plants and the water helps avoid rotting.
Wick and Drip Systems
The water level in wick and drip hydroponics should stay sufficiently high for the systems to work. Aggregates such as rock wool or sand provide the growing medium for plants in wick and drip hydroponics. In wick systems, nutrient solution flows from a reservoir through wicks to the growing medium. Drip hydroponics also supplies nutrient solution from a reservoir, but through drip irrigation. In both systems an air pump circulates solutions to add oxygen. The water level for each system is unimportant, providing it's sufficiently high for the system to run. If the water level in a wick system falls so low that the wicks dry out, apply solution directly to the growing medium and wet the wicks thoroughly to restart the process.
Nutrient Film Technique
A film of nutrients dissolved in water feeds plants growing in a nutrient-film technique hydroponics system. Plants grow in holes in plastic tubing, such as PVC pipes or closed gutters, with their roots inserted into the tubing and their top growth protruding out. A constant stream of shallow water passes over plant roots at a level high enough to coat the lower plant roots but not so high that it fills the tube and emerges from the planting holes. The tubing sits at a slight angle so that the water flows constantly downward.
Ebb and Flow
Ebb and flow hydroponics submerges plant roots in water at fixed intervals. Plants grow in a soilless growing medium in growing trays, and a pump floods the trays with water and drains them later at timer-controlled intervals. Plant roots are constantly moist but never submerged so long that they die. The number of times the plant roots require flooding depends on the plant sizes, the growing medium, the temperature and humidity, and the water level is high enough to wet the plant roots but not overflow the trays.
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