Crabgrass is an annual weed that can overrun lawns and flowerbeds. Crabgrass is difficult to eliminate in the adult stage; the best ways to kill crabgrass involve elimination of seeds and young plants as well as proper maintenance practices.
The best way to kill crabgrass is to control the spread of seeds. Stopping the spread of crabgrass seeds will keep this weed from coming back the following season. Keeping the edges of driveways and walkways clear of debris and grass will deny crabgrass seeds of a reservoir for gathering. Not allowing crabgrass to become full grown and go to seed is another way to kill crabgrass effectively for the following season.
Maintaining proper shade in areas also kills crabgrass. Mowing grass to a minimum height of 3 inches eliminates sunlight from reaching the ground; crabgrass requires lots of sun and is a low-lying plant. Keeping other plants at 3 inches or higher will shade the area and kill crabgrass.
Keeping soil in lawns and landscaped areas deeply irrigated provides needed moisture for grass and plants while keeping water below the top level of soil. Crabgrass has shallow roots and requires moisture near the surface of the ground to grow. Allow the top layer of soil to dry out during wet or rainy seasons; avoid watering the area if it has rained within a 48-hour period.
Remove dead plants to help turf grass or other plants re-establish themselves in the area. Removing young plants removes the chance of seeds spreading. Maintaining a healthy lawn is the easiest method to kill crabgrass. Avoid over-fertilization to starve crabgrass of needed nutrients. Replace bare spots with new grass seeds or plantings. Cover non-lawn areas with a thick mulch layer of between 1 and 2 inches, which shades the ground beneath and deters crabgrass from growing.
These are products that inhibit crabgrass seeds from sprouting. There are natural and chemical varieties available. Use pre-emergents during the early days of the growing season for your area. Crabgrass starts its growth cycle before turf grass.