We have a problem with crabgrass (smooth or large unsure) and I have...

Asked April 21, 2014, 3:41 PM EDT

We have a problem with crabgrass (smooth or large unsure) and I have purchased a pre-emergent (Scotts which also contains fertilizer). The information I have found is confusing and contradictory and the instructions say to wait two or three mowings (which seems way too late to me). When is the best time to apply this? How do I know when these little beasties are germinating? Also, when can I re-seed the lawn with the grass that I want growing? Last year I applied an herbicide to kill the dandelions, clover, and other broadleaf weeds which worked quite well but left bare spots which were immediately taken over by the crabgrass. Thanks for any information you can give me. I can't really afford a lawn service.

Hennepin County Minnesota

1 Response

I may have to hedge my response based on the formula of the pre-emergence you actually purchased. If you read the back of the baq carefully, it should tell you if it is only a pre-emergent or if it also is a post-emergent. Some of those combinations are now available which makes it less critical as to timing. Crabgrass is an annual which comes back from seed. Also, the area next to a street/drivewayi/sidewalk warms quicker than the rest of the yard. We often state that crabgrass will sprout about the same time as lilacs bloom. However, you should apply it to the border areas I list above a week or so prior to that time. If you don't have lilacs try thinking about the time your shrubs start to leaf out as the correct time for those areas. Also check the bag for information as to how long it is effective. If its a period of several weeks, you can apply it earlier and be assured that it will be there when needed. That also is your guide to re-seeding. The pre-emergent will prevent crabgrass seed from germinating but also prevent your replacement grass seed from germinating until it loses effectiveness.