How to Dethatch a Lawn and Why You Need To

Removing excessive thatch an essential part of keeping grass healthy

Raking a lawn

The Spruce / David Karoki

In lawn-care practice, the term "thatch" refers to the layer of organic material that lies between the living grass blades and the embedded roots and soil layer below. It is a mat-like layer that includes dead grass blades, mulched leaves, and other debris. This organic layer of thatch is quite useful in moderation, as it provides several elements necessary for lawn health:

  • Moderates soil temperature swings
  • Preserves soil moisture
  • Maintains a uniform soil pH of about 6.5, ideal for turf grasses.
  • Provides nutrients as organic material steadily breaks down
  • Blocks out burrowing pests.

While "organic" is usually thought of as a good thing, this layer of organic thatch can become a problem if it grows too thick and impenetrable. When this happens, it requires a lawn-care process known as dethatching.

Once regarded as a required yearly lawn-care activity, dethatching is now approached more strategically, and many lawn care experts caution against doing it too often or with lawns that don't absolutely require it. The hard, deep raking involved in dethatching can tear at grass roots and even open up the lawn to disease and pest problems. Dethatching can cause significant lawn damage if it is done when it is not needed. There are several other reasons why you might want to avoid dethatching:

  • Vigorous dethatching exposes soil and causes faster moisture loss.
  • Dethatching can make it easier for lawn weeds to germinate.
  • Lack of thatch deprives grasses of essential nutrients.

Thus, rather than assuming your lawn requires yearly dethatching, diagnose your lawn first to decide if the advantages outweigh the drawbacks.

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 decomposed. Mulched leaves and other organic material are also found. Removing this thatch with a manual rake or power dethatcher is known as thatch removal.

When to Dethatch Your Lawn

The mere presence of thatch does not mean that your lawn is in need of dethatching. A thatch layer up to 1/2 inch thick is advantageous and can work hard to make soil conditions ideal for growing grass. A modest thatch layer functions much like 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.
  • Provides a breeding environment for insects.
  • Fosters some lawn diseases, especially fungal diseases.
  • Creates a lawn that is spongy underfoot, and difficult to mow.

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. Although there is no hard-and-fast rule, dethatching is often done at different times depending on where you live and what type of turf grass species you are growing.

Cool-season grasses are coming into their prime time for growth in early spring and in early fall. Dethatching at these times is ideal because the grasses will recover more quickly from the stress of being dethatched. And these times just happen to coincide with 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. You should 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.

Tip


New lawns, whether started from sod or seed, should not be dethatched for several years until they become established with good root systems. Dethatching a new lawn can cause considerable damage, especially if it is done with power equipment.

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.

Bird's eye view of grass
The Spruce / David Karoki

Dethatching as Part of Lawn Care

When prevention fails, the solution lies in dethatching. "Dethatching" a lawn refers to the mechanical removal of a thatch layer that is too thick. As a lawn care project, dethatching is not nearly as common as mowing or fertilizing. In fact, some homeowners may never need to ever dethatch the lawn. Or, it may be necessary only every few years. 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.

Don't confuse dethatching with another important lawn care routine— core aeration. Although these activities are sometimes confused with one another, they are entirely different procedures. Performing core aeration does not dethatch the lawn, nor does dethatching offer the same benefits as core aeration.

Dethatching vs. Core Aeration

Dethatching is a mechanical action designed to remove an excessively thick layer of organic material that has not yet broken down into a form that provides nutrients for the lawn. Removal of this thick layer is important because doing so allows water and fertilizer to penetrate down to the grassroots.

Core aeration, on the other hand, is a process by which many small plugs (cores) of turf with attached roots are removed from the lawn, leaving small cylindrical holes through which air can penetrate into the root layer. It is not the same as dethatching, though regular core aeration can slow the buildup of thatch by introducing plenty of air and water down into the thatch, thereby speeding the breakdown of organic material.

Thus, dethatching and core aeration offer different benefits to the lawn. Depending on the condition of your lawn, you may find that your annual lawn care routine requires one or the other—or sometimes both. Some lawn care experts advise that core aeration is the more valuable procedure, as dethatching can badly damage sensitive grassroots if it's done unnecessarily. Dethatching has considerable value if your lawn has a very thick layer of thatch, but if the layer is relatively thin, as is the case with many lawns, dethatching can actually have a negative effect on a lawn's health.

Core aeration, on the other hand, is almost always beneficial to a lawn, and should be done every few years, regardless of whether you are dethatching the lawn. Core aeration is especially valuable if the lawn is badly compacted, which can easily occur in family yards that see a lot of foot traffic and sports activity.

Although there are manual devices that will let you aerate your lawn, one or two plugs at a time, they are not very practical. In most cases, you will either rent a power aerator or hire a lawn service to perform core aeration.

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How to Dethatch Your Lawn

Dethatching is an easy DIY project because it can be accomplished with a simple rake, using an action that is not much different than raking up fallen leaves. As you rake, push the rake tines deeply down through the grass, so that they reach the thatch layer that lies beneath. It can be hard work to dethatch an entire yard with a manual rake, but it is not at all complicated.

A convex or "dethatching" rake is better than a regular leaf rake for dethatching a lawn. A rigid garden rake (bow rake) is another alternative. And so-called power rakes or vertical rakes, which can be rented from a rental center, are the best choices of all. These are used in much the same way as a power lawnmower: You simply criss-cross the lawn with a series of parallel passes, then clean up the massive amounts of loose thatch that are dislodged from the base of the grass blades. (There are also dethatching attachments that replace the cutting blade on a power lawnmower, though these can damage a lawn unless used very carefully.)

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. Annual vigorous raking with a manual rake is a much better option than the potential damage caused when a power rake tears into a thick thatch layer.

What to Do After Dethatching

Dethatching tends to loosen up the soil at the base of the grass blades and reveals some bare soil where the thatch has been removed. Thus, this is a good time to overseed your lawn with additional grass seed and to apply whatever fertilizers or soil amendments that are appropriate. It's a good idea to have a soil test done every few years and to apply whatever amendments are recommended by the testing agency. For example, your lawn may require lime to restore pH balance, or gypsum to loosen the soil and encourage good root growth.

This kind of comprehensive lawn care routine should usually include core aeration, which is best performed immediately after dethatching, but before overseeding and amendment/feeding.

When to Call a Professional

Dethatching a lawn is not a complicated project, but it can be time-consuming and hard physical work, especially if the thatch layer is very thick and dethatching hasn't been done for many years. Because lawn-care professionals have the equipment to do this work quickly, it may make sense to simply hire someone to do this work, especially if you're already hiring professionals to do other seasonal lawn care work, such as core aeration. Pros are familiar with using power dethatchers, and are less likely to damage the lawn than a homeowner using a rental tool for the first time.

Hiring a pro may also be a good idea if your lawn is too large for you to comfortably manage. A long weekend of deep raking can be a grueling process, and spending a couple of hundred dollars for professional dethatching may seem like a bargain.

But once you get into a routine of vigorously raking your lawn each fall or spring, then it becomes a much less difficult task and one that most homeowners will have no trouble doing themselves. If you are already raking up fall leaves, then expending a little more effort to rake down to the thatch layer is well worth the effort.

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