What if you can't use pre-emer, or chemicals to kill the crabgrass? I know that crabgrass is a annual weed and will most likely be killed as the first frost comes in fall. (in Canada), but the seeds will remain on the ground, therefor creating new plants in spring. Is crabgrass a type of weed that does not tolerate frequent mowing? If so, frequent mowing would eventually kill the crabgrass? What are the other ways you can "Naturally" kill the crabrass? I am speaking of mostly Kentucky blue grass lawns, kentucky is good for choking out weeds at a 3" height, but crabgrass grows higher and sooner than that. Any help would be appreciated.