Crab Grass

Asked August 24, 2020, 1:06 PM EDT

Hi, Most of my lawn is covered with crab grass. I also have a lot of bare areas where there is shade. I had one yard company tell me that because I have so much crab grass that he thinks I should spray those areas and then aerate in the spring and put in a crab grass preventer then and wait to over seed until the following fall. He said if I aerate now and seed it won’t get through because of how thick the crab grass is. He did say to bring in dirt and seed the bare areas this fall. He said to be sure and not spray those areas. Do you think this is a good plan? I am thinking about selling my house and really want to get these bare areas taken care of. I know we will have to find good shady grass seed. Thanks, Nancy

Benton County Minnesota

1 Response

I think the advice you received was mostly accurate. Crabgrass is an annual, so applying herbicides in the late summer or fall won't do anything that the first frost can't accomplish. Pre-emergence herbicides should be applied in mid April to mid May before the crabgrass comes out of the ground. Post-emergence herbicides should be applied in mid May to early June to small, visible crabgrass.


Mechanical practices are also important for managing crabgrass. Mowing grass to 3-4" and pulling small infestations by hand before they spread can reduce the overall numbers of plants. The best defense for weeds is a dense, healthy turf, and early autumn and fall are the best times of the year to make sure next year’s weeds do not have a place to fill.

In cases with currently greater than 20% weed cover, consider overseeding to ensure all voids left by the dying summer annuals are filled prior to their germination the following spring. Overseeding can be done this year (now through mid-September) in preparation for next spring. You'll want to get good seed to ground contact, so raking away dead plant material is important. If overseeding in the spring, especially after applying an herbicide, removing the dead material will give the seeds their best chance at taking root.

Herbicides used for crabgrass should be safe for most lawn grasses (be sure to check the label). For shady locations, look for seed mixtures specifying shade tolerance. These will contain fescues along with some common and shade-tolerant Kentucky bluegrasses.For more specific recommendations for grass seed mixes go to this link: https://extension.umn.edu/lawn-care/renovating-lawn-quality-and-sustainability#seed

This link includes herbicide options for crabgrass: https://apps.extension.umn.edu/garden/diagnose/weed/idlist.html#Crabgrass The chemical name is listed, not the trade name you'd see in a store, but you can do an internet search to find herbicides that contain the specific chemical. Typically any herbicide that can be purchased by homeowners can be found in garden or hardware stores.

A herbicide label is a legal document. Always follow the herbicide label directions attached to the herbicide container you are using. Herbicide labels may change frequently. Internet labels may not match the label on the container you are using. The site of use or plant to which the herbicide is to be applied must be listed on the label or the herbicide cannot be used. Remember, the label is the law.