There is a debate going on among our employees about when to dethatch a lawn. Some the guys here say you should do it in the spring when the grass has established its root base. They base their opinion off of what golf courses do for their grass in the spring. Others, like myself, believe it should be done in the fall. If you dethatch your lawn late in the summer/early fall lawns are less susceptible to weeds and crabgrass establishing themselves. Whether you dethatch in spring or fall you need to make sure to give your lawn a healthy drink afterward. At least a 1/2 inch of watering should be done. If you dethatch in the spring you are going to want to make sure to use a fertilizer with a weed killer or crabgrass killer in it after you are done. Here are a few articles I have found to support only my argument. If the other guys in the store want to defend themselves they’ll have to start their own blog:)
Late summer lawn care:
Lawn aerification: If your lawn has significant compaction problems, the period right around Labor Day and through the early fall is an excellent time to do some core aerification. Lawn aerification machines are usually available through most rental businesses.
Be sure to rent a core aerifier, one that actually pulls cores out of the soil and redeposits them on the lawn or soil surface. The extra aeration in the soil will encourage more active root growth as well as benefit the soil microbial community. Healthy plant roots and a healthy soil microbial population make for a healthy, vigorous grass plant better able to withstand stress along with normal wear and tear of lawn activity. The cores can be left on the soil or lawn surface to naturally decompose. This will also help control the buildup of thatch in the lawn. It is best to make two or three passes over the lawn to increase the number of holes needed to maximize the benefit.
Thatch control: Occasionally, a thick layer of brown fibrous material will build-up between the soil surface and where the grass plant shoots begin to turn green. This brown fibrous mat is known as thatch. It is actually composed of both living and non-living material. Thatch develops from the regular sloughing off of plant roots and other dead and decaying parts of the grass plant. It is however, NOT composed of any grass clippings. While there may be some grass clippings left on the surface, they are not part of the true thatch layer. So, whether you pick up your clippings or not, it will make no difference on the build-up of thatch. The living component of thatch consists of some roots, rhizomes and, of course, the many microorganisms and other living creatures.
If thatch develops at a faster rate than can be broken down by microorganisms, it can accumulate to undesirable levels. Generally, thatch greater than half-inch is undesirable. Cultural practices that contribute to thatch buildup are excessive nitrogen fertilizer, overwatering, infrequent mowing, compacted soils and simply the genetics of the particular grasses. Some grasses are more prone to thatch build-up than others.
Photo 3: Vertical mower or dethatcher; sometimes referred to as a power rake. Bob Mugaas.
Late summer (i.e., early September) is a good time to work at removing excess thatch build-up. Machines known as vertical mowers or de-thatchers can be rented and used to mechanically remove some of the thatch build-up. Leaving the soil cores on the surface will also help begin to break down thatch. In fact, where very thick thatch layers exist, using both a vertical mower and core aerifier may be helpful. If this is the case, thoroughly aerify the lawn, than perform vertical mowing. This operation can be done back to back on the same day if desired. It’s a good idea to follow-up with a quarter to half-inch inch of water to reduce lawn stress incurred from the dethatching and aerification processes.
Taken from the University of Minnesota extension page http://blog.lib.umn.edu/efans/ygnews/2009/09/checklist-for-late-summer—ea.html
If your lawn has been damaged by the recent drought conditions, chances are that you will have to do some lawn repairs come fall. Depending on the extent of the damage it might be beneficial to dethatch your lawn. There are several ways to remove thatch from a lawn from manual removal to using power equipment. Thatch rakes are found at most home improvement stores. These rakes have sharp, claw like tines that grab thatch and remove it from the lawn. This is the most labor intensive way to remove thatch. If you are dethatching a small patch of lawn it might be easier to dethatch the lawn by using a thatch rake. Anything over a couple of hundred square feet is best left to power equipment. Most folks do not have hours to dedicate to the manual removal of thatch.
The most effective way to remove thatch in a lawn is through the use of a power rake. Most homeowners do not own a power rake, but they can rent one at most rental stores. Power rakes are about the size of your average push mower and can be used by almost anyone. Most power rakes on the market are constructed using metal blades that spin on a drum. The blades are usually serrated, which allows them to grab the thatch in the lawn. Power rake blades spin continuously while the machine is being propelled forward. Most units come with a bagging system to catch the removed thatch. There are adjustable settings on most machines which allow the user to choose the depth of the blades. You only want to set the blades low enough to remove the thatch. If your blades are removing chunks of dirt and living grass, then your machine is set too low. Any rental store should provide instructions on how to properly use the machine prior to renting it out.
taken from clean-cut property services http://cleancutproperty.com/529/dethatching-drought-damaged-lawns/
Here’s a few more articles about lawn care, seeding, dethatching and aeration: