Is It Safe To Use Grass Clippings From Treated Lawns In Garden Beds?

There are many ways to repurpose your lawn clippings. You can use cut grass for compost, organic fertilizer, eco-friendly mulch, or even animal feed, so long as it hasn't been treated with herbicides. Grass clippings are also useful for gardening and are a cheap, easy way to nourish the soil and protect your plants. But as with the previously mentioned uses, if you treat your lawn with weed killers or pesticides, you shouldn't use such clippings in your garden beds as mulch if you want to grow a healthy garden.

Herbicides and pesticides are great for keeping unwanted guests out of your yard, but while the chemicals are safe for grass, they may not be safe for other plants on your property. Chemical treatments, especially weed killers, can linger for months. If you use clippings from treated grass in your garden bed(s), these chemicals can leach into the soil and harm the growth of your fruits, flowers, and vegetables. They may even kill some sensitive plant species outright.

When it comes to treating lawns with herbicides, the error is assuming other plants in your lawn or garden won't be harmed by these same chemicals or that the residue isn't enough to cause damage. As noted, weed killers, specifically, can persist for months after its application. One study, published in HortScience, found that some common pesticide residues, when applied in two days after pesticide treatment, killed certain plants: tomato, bean, and petunia. In other cases, plants exposed to the treated grass-clippings mulch were injured.

So, if you can't use the clippings in your garden, what should you do with them? The safest way to reuse treated grass clippings is to leave them on your lawn. This is especially important for the first three cuttings after applying the treatment, as it gives the chemical herbicides and/or pesticides time to break down naturally.

After three mowings, the treated lawn clippings, according to the University of Missouri Extension, can be added to a compost pile — provided you didn't reapply weed killer. However, you still shouldn't use the fresh grass clippings directly in garden beds as mulch; it's safer to compost them first.