Originally Posted by
kimini
People figured out that they couldn't keep the grow beds full of water because it drowns the plant roots. Someone came up with the idea of using a small pump to constantly add water to the container, and when it gets about 2" below the surface the media, the siphon dumps all the water out in short order. As the water drops, it sucks air into the grow media, ensuring the roots are exposed to some air in the "soil". The expanded clay holds water long enough to keep the roots happy until the next cycle, though some people use simple gravel because of the much lower price.