Crabgrass is an annual plant that propagates by small seeds. The seeds fall from last year's growth, and remain dormant until mid May. Full exposure from the summer sun allows the invasive plant to thrive. One method of controlling this grass in lawns is to raise the lawn mower's height. This will cause the seed to be shaded from the sun. A pre-emergent herbicide can also be applied to the area to kill the plants just as they begin to sprout. A last resort is to physically burn the plant's seed heads as they develop during the late summer.
Raise the level on the lawn mower. Cut the lawn, leaving the overall height higher than you may normally. The taller grass will shade the crabgrass seeds. This lack of direct sunlight will diminish the chances of the crabgrass seed germinating. Typically one season is all that is required for eliminating crabgrass from an area.
Apply a pre-emergent herbicide to the lawn or garden area on a regular schedule for one season. Consult your local agricultural extension service for recommendations of the chemical product. There may be various strains or species of crabgrass that may require different herbicide applications.
Mix the pre-emergent herbicide in the sprayer. Apply the herbicide according to the manufacturer's instructions. Be careful of any over spray to areas that may contain seeds or young plants, as the herbicide may adversely affect those plants.
Use a propane powered plant burner to eliminate the crabgrass and the seed heads. The powerful weed burners will literally scorch and kill all plants that fall under the powerful flame. While using the weed burner may be more labor intensive, you can accurately control where the flame is directed. Using a propane weed burner is also an organic method of eliminating weeds from a garden area.