When should you apply crabgrass preventer?

Apply crabgrass preventer in mid-spring, before dormant seeds germinate. Use preemergence herbicides while the soil temperature is between 50 and 55 degrees Fahrenheit. Local forsythia will be in bloom.

If the herbicide is applied too early, the chemicals will break down and not be as effective, but turf must be treated before the soil temperature reaches above 62 degrees in the top 2 inches of soil. According to Michigan State University, the herbicide will create a barrier that prevents the crabgrass from growing when the weather gets warmer. It is too warm to apply crabgrass preventer when the blooms drop from the forsythia.