A lush and thick lawn will naturally compete against crabgrass, and healthy grass will usually prevail. If a lawn has bare spots with soil showing through, crabgrass often establishes in the bare spots. Because crabgrass is an annual grass, every spring a gardener has another chance to prevent a new season of crabgrass from gaining a foothold in a lawn. Use pre-emergence herbicide in the spring to prevent crabgrass from growing amongst your healthy grass.
Apply the pre-emergence herbicide to the lawn before crabgrass germinates in the spring. Because crabgrass will quickly germinate once soil temperatures reach 60 degrees F, you must apply the herbicide/fertilizer combination prior to the crabgrass germinating. Consult the herbicide/fertilizer package for the recommended amount of herbicide for your lawn area and fill the broadcast spreader with this amount of fertilizer. Push the broadcast spreader over every area of your lawn to prevent the crabgrass from germinating.
Set the lawn mower height to 2 1/2 to 3 inches and keep the grass at this height during the entire growing season. Grass this height will be dense and strong enough to choke out crabgrass. Mow the grass once or twice per week to keep your grass at the optimal height.
Water the grass only during dry periods and then water the grass deeply. If you water often and shallowly, you encourage crabgrass growth. Wait until you see indications of drought by waiting until the grass turns bluish and stays matted down when you walk on it.
Avoid fertilizing a lawn with a nitrogen fertilizer in the middle of the growing season because this will promote crabgrass growth. Fertilize the grass again in early autumn and a final time after the last mowing of the growing season.