Hydroponics, the soilless culture of plants, has fascinated the public for decades. This important research tool has been used for well over a century to study plant growth and mineral nutrition. The two main types of hydroponic culture are aggregate and solution culture. In aggregate culture, plants are grown in a solid substratum such as sand, gravel, vermiculite, or rockwool. The plants are irrigated frequently with a nutrient solution containing a full range of essential elements. In solution culture, by contrast, plant roots have no solid support but constantly are immersed in the nutrient solution.