Growing plants in aggregates such as sand or gravel is often preferred to the water culture method since the aggregate helps to support the roots. The aggregate is held in the same type of tank as is used for a water culture system. The nutrient solution is held in a separate tank and pumped into the aggregate tank to moisten the roots as needed. After the aggregate has been flooded it is drained to provide aeration. Enough water and nutrients cling to the aggregate and roots to supply the plant until the next flooding
The solution is generally pumped to within 1 inch of the surface and then allowed to drain. If the top surface of the bed is kept dry, the growth of algae will be minimal. To allow rapid drainage, the aggregate must be coarse. Use sand with particles of at least 1/16-inch diameter or gravel of about 1/4- to 3/8-inch diameter. The best aggregates are silica gravel, granite, basalt, or smooth river-bottom rock of the inert type that contains no calcium. Larger aggregates will require more frequent flooding, whereas smaller aggregates will not drain properly. In small, experimental units you may use any of several different substances. Perlite, Styrofoam, and crushed marbles have all been used successfully by hobbyists.
The aggregate should be flooded for about 10 minutes and allowed to drain for no longer than 30 minutes.