Dethatching Lawns: What, Why, How, and When

Removing Excessive Thatch an Essential Part of Keeping Grass Healthy

daughter and mom raking grass

CasarsaGuru / Getty Images

"Organic" is usually thought of as a good thing, but the organic thatch can become a problem, necessitating the dethatching of a lawn. Here is why.

Think of a lawn as having three levels:

  • The grass blades, themselves: This is the level that you see. You will observe the results of your lawn care efforts at this level, but much of the "action" takes place at a lower level.
  • The soil
  • The layer of thatch between the grass blades and the soil

Having a green lawn starts with having good soil, in which the roots of your grass reside. An ideal soil is one that:

  • Is kept evenly moist
  • Has good aeration
  • Has a pH level of about 6.5
  • Enjoys sufficient nutrients

What Is Thatch Removal?

In a lawn, the thatch is an organic layer made up primarily of grass stems, stolons, and rhizomes (both living and dead) that have not yet broken down, or decomposed. Removing this thatch with a rake is known as thatch removal.

When to Dethatch Your Lawn

A thatch layer of 1/2 inch can work hand in hand with these soil requirements. Such a thatch layer functions as if it were a mulch. It moderates the temperature of the soil and helps it retain moisture. As microbes in the soil break it down, nutrients are released into the soil.

But sometimes the organic matter that makes up that thatch layer accumulates faster than it can break down. It becomes too thick (1 inch or thicker), leading to the following problems:

  • It forms a barrier that deprives the root system of air, water, and nutrients.
  • It promotes insect infestations.
  • Lawn diseases are more likely to take hold.
  • Patches of lawn with thick layers of thatch become spongy. When mowing your lawn, the mower wheels sink down in these areas, resulting in a lower cut. This keeps you from mowing your lawn at the ideal height.

You do not even necessarily have to measure the thatch layer to determine that it is problematic. Simply try to poke your finger through to the soil: If it is too hard to do so, then you probably have a thatch problem.

Preventing a Thatch Problem

Since a thatch problem is the result of new organic matter building up more quickly than the older organic matter can break down, avoid practices that result in your grass growing too quickly. For example, do not:

  • Water the grass more than is necessary
  • Feed it with a fertilizer that is high in nitrogen

Staying away from the unnecessary use of pesticides also may help you avoid having to dethatch your lawn. Worm presence helps in the decomposition of thatch. Pesticides, unfortunately, kill worms.

Dethatching As Part of Lawn Care

When prevention fails, the solution lies in dethatching. "Dethatching" a lawn refers to the mechanical removal from a lawn of a thatch layer that is too thick. Dethatching is not nearly as big a part of lawn care as is mowing. In fact, some homeowners may never need to dethatch the lawn. Some types of grass simply are not as susceptible to thatch build-up as others. For example:

  • While Kentucky bluegrass (Poa pratensis) is one of the cool-season grasses prone to developing too much thatch, tall fescue grass (Festuca arundinacea) is far less susceptible.
  • Among the warm-season grasses, you are more likely to have to dethatch Bermudagrass (Cynodon dactylon) than zoysiagrass (Zoysia japonica).

But when thatch does become a problem in a lawn, you should not overlook the importance of dealing with it, because the long-term health of your grass hinges on your finding a solution. The solution can take either of two forms: dethatching or core aeration.

How to Dethatch Your Lawn

Dethatching is the easy option because it is accomplished simply by using a rake. Push the rake tines deeply down through the grass, so that they reach the thatch layer that lies beneath. If you have a cool-season grass, you can be dethatching your lawn at the same time as you rake it for other reasons. Here is why:

Cool-season grasses are coming into their prime time for growth in early spring and in early fall. Dethatching them at these times is ideal because they will recover more quickly at these times from the stress of being dethatched. These times just happen to coincide when you will be raking to clean up the lawn in early spring and raking leaves off the lawn in the fall.

It does not work out quite so conveniently for homeowners with warm-season grasses. Dethatch lawns composed of warm-season grasses in late spring, which is just when they are "coming into their own" and will recuperate fastest from undergoing dethatching.

A convex or "dethatching" rake is better than a regular leaf rake for dethatching a lawn. And a so-called "power rake," which can be rented from a rental center, is the best rake of all. But do not stress over the type of rake you use. Any deep raking that you do is better than nothing, especially if you faithfully rake every year.

Dethatching vs. Core Aeration

Of the two solutions, dethatching is certainly preferable to core aeration because core aeration requires a mechanical device. Unhappily, you may not have a choice. The severity of the situation determines which solution is implemented. Dethatching is for mild cases. You will know afterward that it worked if your grass starts looking better the following year.

If grass health does not pick up, that could mean that you have a more severe case. Core aeration may be necessary for your lawn. It is best performed in fall. If you have badly compacted soil, that is another reason to aerate your lawn.

You have three options when it comes to core aeration:

  • Hire a lawn service to do the job.
  • Rent a core aerator.
  • Buy an aerator.

The average homeowner should be able to either hire a lawn service or to rent a core aerator. When it comes to buying, not only is cost an issue but so is storage. Dethatching a lawn by means of a core aerator is probably not going to be a yearly task. Whenever it is not in use, this large piece of equipment will be taking up space in your garage or storage shed. An exception might be made if you own a tractor or a riding lawn mower because you can buy an attachment for these machines that will allow you to aerate your lawn.

If you are not physically up to the job, do not live near a rental center, or just plain do not like gadgets very much, it might make sense for you to choose to hire a lawn service to do this work. Otherwise, renting is a great option.