Asked August 19, 2018, 11:45 AM EDT

What can I spread over mulch to prevent weeds? At age 76 I have mulching done. However, it doesn't take long before weeds appear on top of the mulch. Is there something easy I can put on top of the mulch (like a granular) to prevent the weeds for 1 year?

Howard County Maryland weeds mulch plant care pre-emergent herbicide weeds growing on mulch

1 Response

It's odd that weeds are growing on the mulch if it's being put down fresh each spring. A few things could account for that:

1) the mulch is too fine and decomposes very quickly (or is is already partially decomposed when spread), so it becomes a growing medium for weed seeds before the growing season is over. The solution would be to request coarser mulch. Also, pine nuggets would work. These both break down much more slowly and should get you through the growing season.

2) There are perennial weeds under the mulch. The top growth dies back in the fall, but the root system is strong and can push through a layer of mulch each year. To solve that, you could either:
- spray those weeds with a systemic herbicide that will go down to the roots and get rid of them once and more all Early fall is a good time for this. Or
- pull them and don't let them do to seed, or
- when mulch is put down, first put down 3-4 layers of newspapers under the mulch. This is a solid barrier that most weeds, annual or perennial, can't get through.

The herbicide you asked about would be a pre-emergent herbicide (granular) such as Preen. You would need to apply it in early fall to kill "winter annual" weeds that germinate in the fall, and apply it in spring for spring-summer weeds.

Please read through this webpage: https://extension.umd.edu/hgic/lawns/control-options

Our weed gallery will tell you how to handle each type of weed: https://extension.umd.edu/hgic/problems/weeds