Vermiculite is a light, spongy material derived from mica. It is used in both horticulture and mycology. In horticulture, the vermiculite particles allow for greater aeration of the soil. They also allow for greater hydration of the soil without the same risk of root rot that over-watering might pose. By using vermiculite, the excess water is stored in the vermiculite particles until it is needed. The spongy texture of the vermiculite soaks up water, releasing it slowly as the external soi...