For Early and Best Control. Crabgrass seeds can germinate each year when nighttime soil temperatures reach over 50 degrees for 3 days. This âwakes upâ the seed, and starts it on its process of growing up to be your worst nightmare.Note, the seed âcanâ germinate at that point.reen Light Crabgrass Preventer covers up 5,000 sq. ft. with a 10 lb. bag, and is safe to use on all lawn types. (IMPORTANT! See note below.). This is one of the few companies that provides the pre-emergent alone, as most want to sell you a combination product with fertilizer.