Asked May 1, 2020, 9:28 AM EDT

How long after using weedmaster broad leaf weed killer on a lawn, can the grass clippings be put on the compost pile (for future garden use).? Can the clippings, before composting, be put around very established shrubs?

Clackamas County Oregon

1 Response

Weedmaster is a combination of 2-4 D and Dicamba

Generally, phenoxy herbicides do not persist more than a month in soil. For example, 2,4-D has a relatively short persistence in soil, with a half-life of 14 days or less. Dicamba, a benzoic acid, and triclopyr, a pyridine herbicide, can last somewhat longer — a month or so in soil — depending on application rate and weather conditions.

For your grass clippings, it will depend on how long they will be in the compost pile before you anticipate using that compost. If it is a slow cooking backyard pile and will be many months before you use it, you can being adding the clippings right away.

There are other herbicides that can persist for 6 months or more and then have seen widespread issues with compost being applied and obvious herbicide damage occurring after. I would encourage you to also read the label on your package to make sure they do not include any additional advisement, there are various strengths of the same brand name and they may have a special statement about compost - I know they are super long and require magnification.