We get asked this question often so I thought I would address it. Of course, if you are going to be using compost on your garden to grow vegetables or flowers you want to make sure the compost is safe.
Many people have concerns about composting lawn grass that has been treated with herbicide and how that will affect their compost. If you are composting residential lawn clippings, then the herbicide that can legally be used on your lawn is required to be able to break down within a matter of a few days and should not pose any further danger to other plants that receive compost made from these grass clippings.
It is not so much a matter of “if” as it is “when” to use grass clippings as an additive to your compost pile. Grass clippings are very helpful in a compost pile to provide the necessary green element that works with the brown elements (newsprint, straw, leaves, manure etc.) to create heat and make the compost cook.
Some lawn care companies do use liquid herbicides that are applied directly to the blades of grass, and I would probably not use those as mulch in flowerbeds but would consider them safe when broken down in an actively cooking compost pile. For grass clippings treated with granular herbicides, once they are watered in and can’t be vacuumed up with the clippings, they should be safe.
In general, plant material with insecticides registered for home use is safe to use in a compost pile. Insecticides sprayed on plant material break down rapidly in light, and the plant material usually can be used in the compost pile within one week of application. Our grass clippings are exposed to light for more than a week and usually longer before we mix them in to our compost.
Remedy If Still Concerned:
If you still don’t feel confident in the above information or you are trying for a more registered organic method, consider this. We sell a product called Soil Diva and Reclaim that will bind with any residual chemicals in the compost or soil. This product works to naturally burn up or dissolve any trace of the elements of concern.