How to Dethatch a Lawn
If you need to dethatch your lawn, you have a few options. If the lawn is small and you like exercise, you can remove thatch manually with a sturdy leaf rake, hoe or inexpensive thatching rake. Rake the built-up brown matter from under the green grass and dispose of it. You can also hire a lawn service to do the job for you.
There are some chemical products on the market that claim to dethatch, but horticulturists say they're ineffective [source: Fagerness]. Small dethatching blades are sold as lawn-mower attachments, but they're not the best choice because they put a lot of strain on the mower.
Most people rent a power dethatcher. Because these machines are expensive and dethatching is necessary infrequently, it rarely makes sense to buy one.
Dethatchers are called such names as vertical slicer, verticutter, vertical mower and power rake. Some have flat steel blades. For bluegrass and similar varieties, wire tines can work. The bladed types typically have flail (rotating) blades or fixed knife-life blades. The flail type is more commonly available. These machines are heavy. You will probably need help loading and unloading.
When you rent the dethatcher, ask for advice about how far apart and how deep to set the blades. If the rental agency can't help, check with your agricultural extension service. Settings differ according to types of grass. Generally, blades should be an inch or two (2.5 or 5 centimeters) apart for tough grasses, three inches (7.6 centimeters) or more for more delicate grasses.
You want to remove thatch that is right above the soil without tearing it up. A height of about a quarter-inch (6.35 millimeters) above the soil may work -- adjust the blades while they are on a smooth surface. They may need to be slightly higher for delicate grasses.
First, mow the grass about half as high as usual. Then make several passes across your lawn with the dethatcher, changing directions to cross previous passes.
Rake up and remove the thatch you loosen. There may be a lot: An average size lawn can yield two or three pickup truck loads. If you haven't used herbicides, the thatch can be used for mulch or compost. If you have used pesticides as recently as a month earlier, discard the thatch.
Read on to learn about why timing is so key to dethatching success.