If theyre beginning to bloom its time to get your crabgrass preventer down. Ad Take Control Of Your Lawn Tackle Unwanted Growth With Tools Products From Top Brands. Vitamin Water Zero Intermittent Fasting In 2021 Lawn Food Crabgrass Preventer Crab Grass You can apply a crabgrass preventer when the soil temperature reaches 55 to 60 degrees Fahrenheit for a few days in a row because thats when the majority of crabgrass seeds begin to germinate. . The best time to apply crabgrass preventer in early spring when soil temperatures start to warm up to 55 F. Soil temperature should be around 55-60 degrees Fahrenheit. For fall the best time is the end of the august month and earlier in October and if you are optimistic to apply crabgrass second application during fall then wait for 28 to 48 days approximately until good control comes and the lawn appears with excellent dormancy for spring. Browse Our Variety Of Weed Control - Great...