Crabgrass is never a welcome addition to anyone's lawn. Bruce Spangenberg, a horticulture educator at the University of Illinois, warns that, as the summer weather gets warmer, you should be on the lookout for the emergence of crabgrass. Dry heat is another welcome mat for crabgrass. As your lawn begins to wilt in the dog days of summer, crabgrass begins to take hold. Your best course of action is to keep your lawn as healthy as possible, so it can be its own defense against a crabgrass invasion.
Set your lawn mower higher. Cutting your lawn to a height of 2 to 2 ½ inches helps to inhibit the growth of crabgrass.
Water your lawn deeply. Create a watering schedule for your lawn in which you water less frequently, but saturate the soil to a depth of 4 to 6 inches. This practice strengthens the root system of your lawn, making it more difficult for crabgrass to penetrate.
Fertilize your lawn. A healthy, lush lawn is the best defense against a crabgrass invasion. The thicker your lawn, the more competition it provides against crabgrass.
Use a post-emergent herbicide to treat crabgrass directly. Spot treat your lawn for visible crabgrass that has taken hold. The sooner the crabgrass is killed, the less likely it will have the opportunity to germinate and spread .