Controlling crabgrass

Asked February 8, 2018, 1:16 PM EST

I have a large garden area that was taken over by crabgrass & weeds last year. This year, in an attempt to better control the crabgrass and make gardening a bit easier, I am moving my garden into raised beds and putting down weed fabric and mulch around the beds. I have read that the best way to attempt to control crabgrass is to put down a pre-emergent in the spring. Do you have any recommendations on what type of pre-emergent to use? Also, is it safe to use it around the raised beds? The raised beds will be about 22" high. Any other suggestions on how to control crabgrass and weeds around raised beds? Thank you.

Washington County Oregon

3 Responses

The only way to eliminate crabgrass is to dig out all the roots as even a tiny bit will regrow. This is generally a long and tedious process. You can try cutting back the turf around the box to 12 inches from the box and to a depth below any crabgrass roots and discarding that soil (or piling it in an out-of-the way place). This should prevent any seeds from the outside areas getting into the box or stolons from the grass crawling under the box. I would think that heavy weed cloth under the box and lack of sunlight would eventually kill any grass underneath the box, so your problem must be originating from plants on the perimeter. Once you have eliminated them, place heavy weed barrier (or a double layer) around the edges of the box. You can cover the cloth with bark or other materials such as gravel. You might also try placing a pre-emergent such as corn gluten on the area. Unfortunately, your only other alternative would be to dig out the boxes and redo the weed barrier (a double layer or better quality) or elevate the boxes (you would have to construct a bottom for them) on pier blocks or other risers.

Thank you for the response. The raised beds this year will be new and in the process of preparing the space, we were able to dig out a lot of the roots. What is a product name or brand of a corn gluten pre-emergent?

A brief Google search suggests a variety of solid and liquid products as unprocessed, granualated and pelletized, available online and in retail garden centers.
As a cautionary note, You should read the OSU Extension Service article "Corn gluten did not prevent weeds from germinating in OSU study" December 1, 2006 by Carol Savonen, before you invest in a corn gluten product and you can thus make an informed decision. It can be costly and needs to be applied under certain conditions applied in early spring 3-5 weeks before weeds begin to sprout. Good Luck!