What is Thatch?

thatch laying on grass

Does walking on your lawn give you a spongy, squishy, or sinking feeling? If so, you may have something called thatch. 

Some thatch helps your lawn, but too much means stunted roots and the potential for fungus and pest problems. We’ll define, demystify, and debunk ideas about thatch so you can help your lawn thrive.

What is thatch?

illustration explaining thatch on grass

Thatch is a layer of undigested roots, leaves, and organic plant material that settles between the turfgrass and the soil surface. If you take a core sample of a thatchy lawn, the thatch layer squishes down and rebounds like a wet sponge. 

The thatch layer not only looks spongy, but it functions as a sponge, as well. Most of the water from rain or irrigation is trapped in this layer of organic matter. This means the grass roots don’t have an incentive to grow deeply in search of water because the water remains at the top of the soil. They stay short and live happily in the thatch layer where they have all the water they need without having to search for it deep down in the soil.

Pros and cons of thatch

Like too much ice cream, too much thatch does more harm than good. Up to one-half inch thick is fine. Anything over that, and you’ll need to remove some of the material. 


A thin layer of thatch, less than one-half inch, provides these benefits to your lawn:

✓ Insulates the soil
✓ Maintains soil moisture
✓ Creates a resilient, soft walking surface
✓ Protects the lawn from heavy foot traffic
✓ Reduces weed germination


A thick layer of thatch, more than one-half inch, can be a detriment to your lawn:

✗ Easier for mowers to scalp the lawn (because the wheels sink into the soil and the crowns are higher than normal)
✗ Shallow root system (roots don’t dig deeply into the soil to look for water)
✗ In hot weather, roots may dry out; in wet weather, roots are too wet and deprived of oxygen
Fungus and pest problems
✗ Prevents air, water, fertilizers, and lawn treatments from reaching the soil level

How to prevent thatch

Even if you have thatch-prone grass (see FAQ #1), there are ways to encourage a healthy climate of microorganisms that break down thatch quickly.

  • Continue to mulch your grass clippings.

Grass clippings do NOT contribute to an excessive layer of thatch in most cases. Leaving mulched grass clippings on the lawn is beneficial in most cases and is a key lawn care practice for a healthy lawn.

  • Follow the “deep and infrequent” rule of watering.

Don’t water your lawn every day, or even every other day, in most cases. (Sandy soils may be an exception.) Aim for about 1 inch of water once per week (also take into account rainy weather). This encourages the grass roots to grow deep in their search for water.

Don’t know if it’s time to water? Let the grass be your guide. Look for wilting or curling leaf blades before you turn on the faucet.

  • Invite more microorganisms into your lawn.

A soil pH of 6.5, along with aerated soil, is an ideal climate for microorganisms that break down thatch. Conversely, compacted, acidic soils with a soil pH of 5.5 or lower reduce the population of beneficial microbes in your lawn.

illustration showing how aeration works and the benefits of aerating soil
  • Go easy on the fertilizer.

Highly managed lawns with too much nitrogen fertilizer encourage too much growth. Excessive root and stem tissue can’t be broken down that fast. In addition, some nitrogen fertilizers lower the pH of your soil and decrease the microorganisms in your lawn.

  • Watch out for fungicides and insecticides.

Thatch problems often develop in high-maintenance lawns. Over several years, regular fungicide treatments can promote excessive root and rhizome growth, which leads to more thatch. 

Certain insecticides decrease the earthworm population in your soil. Since earthworms help stimulate soil microbial activity, fewer earthworms mean less thatch is decomposed in your lawn.

  • Follow the one-third rule of mowing.

If you cut no more than one-third of the grass blade per mow, you reduce thatch production in your lawn. How? The tips of the grass are usually only leaf tissue, which is mostly water. If you cut more than that, you may cut more of the stem, which breaks down more slowly than the leaf.

illustration explaining the one-third rule for mowing grass

How do I get rid of excess thatch in my lawn?

There are several ways to reduce excess thatch. From our “How to prevent thatch” section above, you can deduce these strategies:

  • Water infrequently and deeply
  • More microorganisms
  • Proper use of fertilizers
  • Nix the insecticides
  • Find alternative ways to treat or prevent fungus (if it’s a consistent problem)

If you want to help the process along:

  • Use a dethatching machine, such as a vertical mower or power rake
  • Apply a liquid dethatcher to the lawn
  • Use a sweat-powered dethatching rake (best for very small areas)
  • Do core aeration, and then apply a layer of topdressing to the lawn 

FAQ about thatch

1. Which grasses develop thatch?

Most grasses that develop stolons (above-ground stems) or rhizomes (below-ground stems) are susceptible to excessive thatch buildup. Grasses with greater lignin content are more prone as well because lignin is harder for microorganisms to break down.

Grass types that are susceptible to thatch:

Cool-season grasses:
Creeping bentgrass 
Creeping red fescue 
Kentucky bluegrass 

Warm-season grasses:
Hybrid bermudagrass 
Centipedegrass (only if over-fertilized) 
St. Augustinegrass

Grass types that are not susceptible to thatch:
Perennial ryegrass (bunch-type cool-season grass)
Tall fescue (bunch-type cool-season grass)

2. How do I know if I have thatch?

The best way is to take a core or plug of soil from several areas in your lawn. If there is a layer of spongy, undigested material between the grass and soil, this is the layer of thatch. 

Ask yourself a couple of other questions:

What type of grass do I have? (See FAQ #1 for grasses that accumulate too much thatch.)
Do you have your lawn on an intensive management program? (Regular nitrogen fertilization, insecticides, and fungicides may encourage excessive lawn thatch.)

If you’re still unsure, take a photo and send it to your local Cooperative Extension office. They’re there to provide expert help to homeowners on lawn-related topics.

3. When is the best time of year to dethatch my lawn?

Dethatch cool-season lawns in late summer or early fall at the beginning of their fall growth spurt. If you have warm-season grass, wait until the grass greens up in late spring or early summer.

If living your best life now means having a local lawn pro demystify your lawn woes, click through to a local lawn care pro today. Our pros take care of thatch, compaction, and other lawn problems to help your lawn thrive.

Main Photo Credit: David Eickhoff | Flickr | CC BY 2.0

Sarah Bahr

Sarah is a writer who has previously worked in the lawn care industry. In her spare time, she likes to garden, raise chickens, and mow the grass with her battery-powered lawn mower.