Crabgrass, a summer annual, has a tendency to make a gardener crabby. As soon as the soil begins to warm in the spring and on into fall, crabgrass can become abundant, spreading by seed and by rooting at the nodes.
Keeping the lawn full and healthy is one way to prevent crabgrass from getting a foothold in the lawn. Once it's there, aside from hand-pulling, the best way to get rid of crabgrass is by using herbicide. Apply the herbicide prior to crabgrass seed germination, generally around mid-March (or when the soil begins to warm to over 50 degrees F), and again in mid-September.
Pour the pre-emergent herbicide granules into the spreader. Crank the handle on the spreader as you walk the lawn, going north to south, in strips. Add more granules to the spreader and apply it as you walk east to west, over the entire lawn. This criss-cross-patterned application will help to ensure even coverage of the lawn.
Water the area until the lawn is completely saturated after application. Water helps activate the herbicide.
Re-apply the pre-emergent herbicide in September, or when the weather begins to cool, in the same manner that you applied it the first time.
Spray post-emergent herbicide directly on young crabgrass that grows during the summer. Cover the entire plant with the spray, until it is wet and dripping.
Prevent crabgrass by cutting your lawn as high as possible for the species of grass you are growing, but at least 2 inches. The longer grass height will create shade, which is the enemy of crabgrass. Watering less often, but deeper (to 4 to 6 inches deep) will keep crabgrass seeds from germinating.