Crab grass is an annual grass that is considered a weed and can take over a yard if left unattended and untreated. Fortunately, taking a few preventive measures can thwart it, saving the trouble of getting rid of it later, which is much harder. Implement as many of the preventative techniques as applicable for greater success.
Mow the grass to a height of at most 2 inches, as a shorter length and bare spots receive more light and air, which are ideal conditions for crab grass to grow.
Seed the new lawn in the fall or early spring before the onset of warmer temperatures, when crab grass begins to grow.
Apply to the lawn ½ to 1 inch of water three or four times a month. More water than that could promote crab grass expansion.
Apply a pre-emergent herbicide in the late winter or early spring, but before soil temperatures reach 55 degrees F. Follow dosing instructions for correct application.