When, Why and How Often to Dethatch Your Lawn

Did you know that your lawn can benefit from a good spring cleaning just like your home? While an indoor deep cleaning removes dust and dirt from ceiling lamps to baseboards, an outdoor “deep cleaning” focuses on eliminating thatch buildup that may be depriving your lawn’s root system of the water, air and nutrients it needs to stay lush and robust.

“Thatch is defined as a tightly intermingled layer of both living and dead plant tissue that exists above the surface of the soil and below the verdure (the green part of the lawn),” explains agronomist and lawn care expert Bob Mann.

“A measure of thatch is beneficial but once the layer has exceeded one-half inch in thickness, it begins to become problematic.”

This is certainly a task most homeowners can tackle. “If you have a dethatching machine or rake and the time, you can remove the excess thatch yourself to restore the health of your grass,” says Midwest Lawn Co. owner Eric Harbit. Before you dive into dethatching, however, read our overview to learn when, why and how often to take on your yard’s thatch layer.

What Is Dethatching a Lawn?

Dethatching is the mechanical removal of thatch, made up primarily of grass, leaves, stems, grass roots and lateral weed growth. It is usually done with a gasoline-powered or electric dethatching machine. But you can also do it by hand with a dethatching rake.

“A healthy lawn needs a thin layer of thatch to work as a barrier between the grass roots and the elements, insulating against extreme variations in soil moisture and temperature,” Harbit says. “When too much thatch builds up over a short amount of time, however, it can cause a number of issues and stifle the growth of your grass.”

Thatch inhibits nutrients, air and water from reaching the root layer of your lawn, resulting in a shallow root system and issues with fungus. Wet thatch can retain too much water during rainy seasons, leaving grass roots susceptible to rot. Grass roots may also grow in the thick thatch layer instead of the soil. This can make your grass weak and vulnerable to drought conditions and other stresses. Dense thatch can harbor insects and diseases and inhibit fertilizer absorption.

To avoid compromising the long-term health of your lawn, it’s important to take care of thatch buildup as soon as it becomes an issue. If your lawn is extremely bouncy underfoot or you can’t see the soil between the grass blades, you may want to check your thatch layer.

You can dig up a small sample of turf with a trowel to measure the thickness of the thatch layer. Or simply try to poke your finger through the grass into the soil. If the thatch is too dense to penetrate, you likely have a problem you need to address.

When to Dethatch the Lawn

Generally, lawns prone to thatch buildup should be dethatched once a year.

“Dethatching is typically done when the lawn is growing and able to repair and recover, and when weather conditions are conducive to survival (not too hot, cold, dry, wet…),” Mann says. In most growing regions of the U.S., this means the spring or fall, when warm temperatures and ample precipitation promote rapid and hearty grass growth.

“Try to avoid times of year when we would expect weed seed germination since the process of dethatching brings seeds to the surface,” adds Mann. This means early spring or the end of September for central latitudes. The season varies for coastal areas and far northern or southern regions.

How Often to Dethatch the Lawn

Some varieties of grass must be dethatched each year. Prime offenders include cool-season grasses like Creeping Bentgrass and Kentucky Bluegrass and warm-season grasses like Bermudagrass and Zoysiagrass, according to Harbit. For other types of grass, thatch builds up over time so you don’t need to dethatch annually.

If you have less thatch-prone varieties like tall fescue or rye, you may only need to dethatch every five years, if at all. No matter what, check your lawn each year to see how much thatch has accumulated.

Can Dethatching Harm the Lawn?

Mann suggests caution when dethatching your lawn. “There’s the possibility of removing too much plant material at once, which would significantly increase recovery time,” he warns. “Also of concern is desiccation. With so many wounds, grass plants may dry out and die.”

If your lawn is already compromised, dethatch with a rake or dethatching machine with rake tines. This method removes the layer of thatch without penetrating the soil beneath. This way there’s less chance of further damaging your grass.

Otherwise, opt for a dethatching machine with thin blades (also known as a scarifier) that cut through the thick layer of thatch into the soil. Scarifiers are much more effective in removing thatch. But be careful; they are also more aggressive and only recommended if your lawn is in good health.

FAQs

We asked Lawnbright founder Craig Elworthy to answer a couple of the most frequently asked questions about lawn dethatching.

What to do after you dethatch a lawn?

After you dethatch your lawn, you’ll want to water thoroughly, and use a quick release liquid fertilizer. This helps the grass quickly recover from stress of dethatching. Also, tread lightly. You can walk on it, but don’t plan to have any backyard barbecues or touch football games on it for the next week to help the recovery process.

Should I dethatch or aerate my lawn?

If you’ve never dethatched or aerated your lawn properly, then you’re overdue for both. However, if you’ve done it in the past few years, then you’ll need to use the screwdriver test. Take a long screwdriver and stick it into the soil as far as it will go; if it goes in easily, congrats! Your soil is well aerated. If it’s hard to get down at least 6 inches, then your soil is compacted and could benefit from an aeration.

Meet Our Grass Experts

• Bob Mann is the director of state and local government relations for the National Association of Landscape Professionals.
• Eric Harbit is the owner of Midwest Lawn Co.
• Craig Elworthy is the founder of Lawnbright; he’s combined his 20+ years of tech experience with his knowledge of lawns to help his clients learn what it takes to fix a patchy lawn.