What is the latest you guys would put down Crabgrass preventer in the spring in northern climates. I am in Milwaukee which is probably a week or so earlier than Minneapolis and a week or so later than central Illinois. I know it all depends on soil temps at 50-55 for 3 consecutive days but I am looking for a guide to use to plan out my first apps. March 15th on a really early year to as late as April 15th on a cool spring????