Crabgrass is a weed that grows quickly and is very stubborn, so it can be hard to eliminate. One of the most ideal ways to get rid of crabgrass is to use a pre-emergent herbicide. It is also important to follow good lawn-care practices in general, in order to make it grow strong and healthy--a strong lawn can choke out weeds before they start.
Pay attention to the date of the last frost in spring before the growing season to apply the herbicide. It is during this time that crabgrass begins to grow. Purchase an herbicide from a local gardening store.
Make sure to wear gloves and to follow the instructions exactly, as amounts that are too large can harm the grass, animals or humans, and amounts too small can be ineffective.
Apply the herbicide according to the instructions. The directions don't vary much for different types, as they all require a couple applications of the herbicide, just at different times. For example, the pre-emergent herbicide Sidurion needs to be applied to the grass when the soil is at 50 to 55 degrees Fahrenheit. Right after application, water your lawn generously.
Don't touch the lawn for about 2 weeks, then apply the pre-emergent herbicide once again in the same way. Water again generously.
Keep an eye on your lawn, and make sure no crabgrass emerges. Treat your lawn properly during the growing season, by watering it once a week (overwatering will make the grass have shallow roots, which will make it too weak to choke out weeds). Also, mow it regularly.