Vermiculite is a lightweight silicate mineral that has the ability to store nutrients for later use. The pH sterile grow medium has excellent water retention, but is often used together with perlite to improve drainage and aeration. Vermiculite is a popular choice for growing in hotter climates There are different types of vermiculite, and some are not intended to be used as growing media. Vermiculite can break down over time, so it is best used with short term crops