How and Why to Dethatch a Lawn

When the layer of organic thatch becomes too thick and impenetrable, it's time to dethatch your lawn. Dethatching a lawn is an easy DIY project, because it can be accomplished with a simple rake. You should not overlook the importance of dealing with problematic thatch, because the long-term health of your grass hinges on dethatching.

Below, we outline everything you need to know before dethatching your lawn and how to get started.

How to Dethatch Your Lawn

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.

Dethatching Tools

However, depending on how much thatch you have to contend with, there are various tool options to get the job done:

• Leaf rake: An average manual fanned leaf rake is the simplest tool but all manual rakes can be laborious to use when dethatching an entire yard.
• Rigid garden rake (bow rake): A manual rigid garden rake (bow rake) with a metal head and tines can be sturdier than a leaf rake to use for dethatching.
• A convex or "dethatching" rake: This specialty manual rake is designed with a head with rows of straight-edged tines on both sides to clear dead matter in the lawn.
• Power rake: There are types of power rakes that can be attached to either a walk-behind or towed behind a riding mower. Another type of motorized dethatching tool looks like a mini-mower that you walk behind to operate. They can be rented from a home improvement center. The blades will usually need adjustment to accommodate your type of grass.

Dethatching Steps

Dethatching uses an action that is not much different than raking up fallen leaves. Once you've chosen a rake, take these steps to dethatch:

1. Use the rake to crisscross the lawn with a series of parallel passes.
2. As you rake, push the rake tines deeply down through the grass, so that they reach the thatch layer that lies beneath.
3. Clean up the massive amounts of loose thatch that are dislodged from the base of the grass blades.

What to Do After Dethatching

Dethatching tends to loosen up the soil at the base of the grass blades and reveal some bare soil where the thatch has been removed. This is a good time to overseed your lawn with additional grass seed and to apply appropriate fertilizers or soil amendments.

Then, water the lawn to relieve it from the stress of dethatching. Core aeration is best performed immediately after dethatching but before overseeding and amendment/feeding.

When to Dethatch Your Lawn

Once regarded as required yearly, dethatching is now approached more strategically, and many lawn-care experts caution against doing it too often. The hard, deep raking involved in dethatching can tear at the grass roots and even open up the lawn to disease and pest problems.

In addition, a moderate layer of thatch can be beneficial to:

• Moderate soil temperature swings
• Preserve soil moisture
• Maintain a uniform soil pH of about 6.5, ideal for turf grasses.
• Provide nutrients as organic material steadily breaks down
• Block out burrowing pests

How do you know you have an overly thick thatch? If the layer of thatch is over 3/4-inch thick, you may need to dethatch. The best way to measure thatch is to dig out a piece of lawn and measure the layer of dead, woody thatch between the soil and the blades of grass. Thick thatch may feel spongy underfoot, as well.

Dethatching is not nearly as common a lawn care project as mowing or fertilizing. Some homeowners may never need to dethatch the lawn. Or, it may be necessary only every few years. Also, some types of grass simply are not as susceptible to thatch build-up as others.

Cool-Season Grasses

Dethatching works best when the lawn is growing and the soil is somewhat moist. Cool-season grasses should be dethatched in the early spring or early fall.

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.

Warm-Season Grasses

Dethatch warm-season grasses when they are growing in the late spring and early summer (after you've mowed once). Among the warm-season grasses, you are more likely to have to dethatch Bermudagrass (Cynodon dactylon) than zoysiagrass (Zoysia japonica).

Why Dethatching Is Important

Dethatching a thick layer of thatch is important to help your lawn stay healthy and thrive. An overabundance of thatch blocks water and fertilizer from reaching your lawn's roots.

When Not to Dethatch

On the other hand, 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.

Rather than assuming your lawn requires yearly dethatching, however, diagnose your lawn first to decide if the advantages outweigh the drawbacks, if you can prevent the problem from developing, or whether you need to perform core aeration, instead.

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.
• Do not feed the lawn with a fertilizer that is high in nitrogen.
• Do not overuse pesticides. Worm presence helps in the decomposition of thatch.

Dethatching vs. Core Aeration

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.

Core aeration is a process of using a manual device to remove small plugs (cores) of turf with attached roots, leaving small cylindrical holes through which air can penetrate to the root layer.

Regular core aeration can slow thatch buildup by introducing air and water into the thatch to speedily break down organic material.

Whereas dethatching may be harmful to your lawn, core aeration is beneficial and should be done every few years. Core aeration is especially valuable if the lawn is badly compacted, which can easily occur in yards with excessive foot traffic and sports activity.

When to Hire a Professional

Dethatching a lawn is not a complicated project, but it can be time-consuming and hard physical work, especially if it is a large lawn, 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 familiar with using power dethatchers are less likely to damage the lawn than a homeowner using a rental tool for the first time.

Once you get into a routine of vigorously raking your lawn each fall or spring, dethatching 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, expend a little more effort to rake down to the thatch layer for a healthier lawn.