My customers sometimes seem to think it has something to do with Forsythia bloom. They get impatient. Preemergent crabgrass control is critical. Lets plan ahead. How many Growing Degree Days (GDD), base 50, does it take to sprout the first crabgrass in your area? Does your local University have a GDD reccomendation, on the best time, or cut-off GDD when it is too late? What is the best date and cutoff date in your area? I have seen university recommendations to stop doing crabgrass at anywhere from 70 to 200 GDD. Myself I think up to 500 GDD works fine. I am satisfied if I get my crabgrass control done by May 10th. I usually do not see visible tiny crabgrass plants until late May.