How late can crabgrass prevention be applied to the lawn? What is the optimal timing in the spring?
Crabgrass doesn’t know the calendar. It only knows the soil temperature. Crabgrass will start to germinate when the soil temperature reaches 50 to 60 degrees at a depth of 2″. Therefore, pre-emergent can be applied until that time, which is usually around the end of May or the beginning of June. The thing to remember is that the crabgrass barrier works for 12 weeks once it has been put down. For folks who get anxious and “must” have their pre-emergent put down at the end of April, there are 4 extra weeks of the crabgrass barrier that will be wasted before emergence of crabgrass. It would be preferable to use those 4 weeks toward the end of the growing season. Thus, optimal timing of pre-emergent is toward the end of May.
