What Are Perlite and Vermiculite?

Vermiculite for gardening

Vermiculite can hold up huge amounts of water — up to 200 to 300 percent of its own weight. Photo credit: Jungle Rebel Flickr

Gardeners often see the ingredients perlite or vermiculite on the potting soil mixture bags. Sometimes they see these minerals listed in soil recipes. The recipe that I like uses vermiculite, but I am switching to coir for environmental reasons. Some recipes call for both perlite and vermiculite because they have different qualities. Here is some information to help you understand these gardening assets.

perlite Maja Dumat

Notice the perlite is white round beads and the vermiculite in the photo at the beginning of the article is brown with irregularly square shapes. Photo credit: Maja Dumat Flickr

Perlite is a treated volcanic glass that gardeners add to condition the soil. The porous material will hold water and release it slowly when the soil dries out. In heavy, clayish soil, it will increase the drainage ability of the soil by loosening up the clay. Hydroponic gardeners use it as a growing medium. People often mistake it for Styrofoam because of its white appearance and tendency to float; but unlike Styrofoam, which is a synthetic plastic, perlite is a natural product.

Vermiculite is mica, a mineral, that retains more water than perlite can. Some gardeners say that it adds minerals to the soil, but it has only small traces of minerals. Vermiculite’s true purpose is to condition the soil and retain moisture. The downside of vermiculite is that companies are mining it to the excess.

When heated, the both perlite and vermiculite swell up. These expanded products have the ability to hold a lot of water, fertilizer, and air. For gardeners, this enhances their garden soil without adding acid or alkaline imbalances. They are sterile, odorless, and do not decompose.

Perlite and vermiculite are finite products, meaning that once the earth’s supply is exhausted, they will be gone. Many gardeners are turning to other products from renewable sources, including coir, mushroom compost, and nut hulls.


Potting Media for Containers at Mohave County Cooperative Extension of The University of Arizona 


A Basic Guide for Beginning Gardeners

What You Should Know about Composting Kitchen Scraps

Coir as a Soil Enhancer 


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