The science of hydroponics is simple. It's basically a way of growing plants in a water and nutrient solution rather than soil. Chances are you've already grown plants hydroponically and didn't realize it. For instance, have you ever rooted a cutting of your favorite annuals or perennials in water? If so, that's a crude form of hydroponics. In this more sophisticated method, the plants grow not in pure water, but in an artificial medium that remains flushed with water and nutrients. The inert "soil" is far less dense than real soil and provides only a structural support for the plant while allowing greater exchange of oxygen.
Modern home hydroponic systems come in a lot of different configurations and are available from various manufacturers at reasonable prices. Gardening by the Yard host Paul James purchased a system that consisted of a plastic planter box with a built-in recirculating pump, a reservoir tray, a bag of artificial earth, and some nutrients. Here's how to set up the system: