Hydroponics is the practice of growing plants in water as opposed to soil. It comes from the Greek hydro ("water") and ponos ("labor"), implying "water working." The essential macro- and micro- (trace) nutrients needed by the plants are supplied in the water.

Hydroponic methods have been used for more than 2,000 years, dating back to the Hanging Gardens of Babylon. More recently, it has been used by plant physiologists to discover which nutrients are essential for plant growth. Unlike soil, where nutrient levels are unknown and variable, precise amounts and kinds of minerals can be added to deionized water, and removed individually, to find out their role in plant growth and development. During World War II hydroponics was used to grow vegetable crops by U.S. troops stationed on some Pacific islands.

Today, hydroponics is becoming a more popular alternative to conventional agriculture in locations with low or inaccessible...