Is vermiculite safe for houseplants? If not, what’s a good substitute?
—Ruth Allen, Snohomish, WA
Vermiculite doesn’t pose a threat to plants. It’s humans who are at risk from exposure to the asbestos that’s contained in some products made from vermiculite. For decades, W. R. Grace and Co. mined vermiculite near Libby, Montana. The asbestos-contaminated mineral was made into home insulation and other products. Though the Libby mine shut down in 1990, vermiculite continues to be mined elsewhere, and in 2000 the U.S. Environmental Protection Agency (EPA) found low levels of asbestos in some soil amendments and premixed potting soils that contain vermiculite. According to the EPA, “Potential exposure to asbestos from vermiculite products poses only a minimal health risk to consumers.”
Despite the minimal risk, the EPA does suggest finding an alternative to vermiculite. Depending on what you use them for, bark, perlite, sawdust, and sand may be good substitutes. If you do use vermiculite, keep it moist to reduce the amount of dust (and asbestos fiber) getting into the air. Use it outside or in an area with good ventilation, and don’t bring the dust inside on clothing or shoes. Choose premixed potting soil over pure vermiculite, as it contains more moisture and is less likely to release asbestos fibers into the air.
To root cuttings, try clean sand or perlite. You can also find horticultural-grade vermiculite over the Internet.