Hi-Yield Crabgrass Control Is A Pre-Emergant Herbicide That Stops Crabgrass And Many Other Weeds From Sprouting In Bluegrass And Many Other Cool-Season And Warm-Season Grasses. Do not use this pre-emergant if you are planning on seeding. If you use Crabgrass control do not seed for 8 weeks. If you have new seeding, do not apply until the new lawn is up and has been mowed three times. Will not harm established trees and shrubs. Will not affect established annual or perennial weeds. Should be applied in spring before new weed seeds germinate. Usually about April here in the northern MidWest. Do not apply too early. In very long growning season areas, a second application may be needed after 10 weeks. 9 Lb. bag covers 2,500 sq. ft. to 5,000 sq. ft. Contains no fertilizer. Does not kill weeds that are already growing.