Many lawns are plagued with crabgrass and fortunately, it can be controlled with herbicides, especially when the crabgrass is still in its early growing stages in the spring or early summer. However, after you have successfully killed the crabgrass, your lawn still might not thrive because the dead organic material can accumulate on top of the soil, under the grass blades. Use a power rake--also known as a dethatcher--to cut vertically into the lawn to bring the dead crabgrass and other dead organic materials, called thatch, up to the top of the grass where you can more easily remove it.
Mow your grass to a height of 1 inch and remove the grass clippings. This will make power raking easier.
Set the blades on the highest setting to start so the rake doesn't dig too deeply into the ground--about 1/8 to 1/4 inch deep is all you usually need. Each power rake is different and every rental power rake should come with a manual. Usually, a the rake has a lever or blade bar to set the height. Ask the rental store personnel to set the blades for you, based on your grass variety.
Push the rake over a small, inconspicuous area first, an area around 10 feet square. Rake up the crab grass and other debris with a lawn rake. Check to make sure it worked effectively and did not damage your lawn. Reset the blades lower or higher, as necessary. Make another pass across the test area. It might take several passes to effectively remove the dead crabgrass.
Rake the test area and see how it looks. If the crabgrass and other dead organic matter is removed and your lawn is not harmed, dethatch the rest of your lawn.