Crabgrass is a summer-weather annual grass that reproduces from small seeds. Crabgrass can spread quickly, due to the small seeds' ability to stick to almost anything and be carried a great distance. The seeds can adhere to lawn equipment, shoes and even birds' feathers. While crabgrass can be removed mechanically by burning, the best defense against crabgrass is keeping a healthy lawn. As a last resort, the application of an herbicide may be necessary once all other natural efforts have been exhausted.
Mow the lawn to its optimal height. Depending on the type of grass in your lawn, this can range from 1/2 inch up to 2 inches in deck height settings for the mower. Crabgrass does not like competition in the area it is growing, so keeping the lawn healthy will go a long way in deterring this annual pest.
Apply a lawn fertilizer several times throughout the lawn's growing season. A vigorously growing lawn will choke out any smaller crabgrass plants. Consult your local home center store or nursery for specific fertilizers that will work best for your species of grasses in the lawn.
Irrigate the lawn on a fairly infrequent basis, such as once a week. According to the University of California, this will cause the lawn to grow with an increased vigor and apply more competition to the crabgrass.
Apply a pre-emergent or post-emergent herbicide as a last resort to rid the lawn of the crabgrass. Your local climate and growing conditions will dictate the type of chemical and the application method. Read all application labeling prior to purchase, as not all herbicides will have the same effect on each species of lawn grass.