Lawn Care Terms: Lawn Thatch

lawn thatch or dead patch of grass
David Beaulieu

By definition, lawn thatch is the layer of mainly dead turfgrass tissue lying between the green vegetation of the grass above and the root system and soil below. A thin layer of thatch in lawns provides insulation against temperature extremes and fluctuations in soil moisture. Generally, a layer of thatch begins to be a problem when it becomes 1 inch thick. The process of getting rid of mild cases of it is known as "dethatching."

Makeup of Lawn Thatch

Lawn thatch consists of stems, stolons, rhizomes, and roots that have not broken down, or "decomposed," yet. Thatch build up begins when turf produces organic debris faster than it can be broken down. If it becomes too thick, this layer blocks air, water, and nutrients from seeping down into the root system, where they are needed to sustain your grass plants properly. A thick layer of thatch also promotes diseases and insect infestations in your lawn.


The issues resulting from a thick build-up of lawn thatch go beyond such reasonably intuitive problems. It may surprise you to learn that it can even prevent you from mowing your grass properly. Spots in your lawn plagued by an especially thick layer of thatch will develop a spongy consistency. When you hit these areas while mowing your lawn, the wheels will sink down, which causes you to scalp your lawn.


The formation of thatch over time is inevitable. Certain practices can hasten the development of an overly thick layer of it, however. Avoid practices that cause your grass to grow at an unnaturally high rate. Too much nitrogen increase the production of root and stem tissue, promoting thatch build up. Thatch accumulates when soil conditions don't sustain a high population of organisms that promote decomposition. Acid soils (5.5 or higher) inhibit microorganisms that break down debris, resulting in thatch build up. Soil with large amounts of clay or sand have a low population of microorganisms, and compacted soil with poor structure also contains low microbial activity, leading to higher build up. Soil tests are a great way to understand your soil's composition and what may need to be added to it for a better lawn.

In terms of practices to avoid, do not, for example:

  1. Water your grass excessively.
  2. Or give it too much fertilizer that is high in nitrogen (the first number in the NPK sequence on a fertilizer bag).

In addition, avoid excessive use of pesticides. Why? Because pesticides can kill earthworms, and earthworms are one of your allies against thatch build-up. At its core, a thatch problem is based on the failure of organic matter to break down properly; instead, it just stays there and forms a barrier. Wherever there is great earthworm activity, the breakdown of organic matter will be hastened.

Moreover, some kinds of turfgrass are known to produce thatch build-up faster; for example:

  1. Among the cool-season types of grasses, Kentucky bluegrass is a prime offender. As an alternative, try growing tall fescue grass, which is less prone to excessive thatch build-up.
  2. You have similar choices with warm-season grasses. Bermudagrass is a worse offender than zoysia grass.

Mitigation of Lawn Thatch

Now you know what lawn thatch is, what causes it, and why it is a problem, but how can you solve the problem? There are two answers, and the right one for you will depend on the severity of your problem: dethatching and aeration.

What Is Aeration?

Aeration is a process used by landscapers and gardeners to allow air and water to permeate the soil beneath grass. Because plants need both elements for survival and growth, aeration is key in keeping your lawn healthy.

In less severe cases, dethatching is a suitable solution. It entails simply removing the thatch by raking it away vigorously. There are special rakes for this work known as "dethatching rakes." A regular leaf rake will not do a thorough job, leaving behind thatch.

In more severe cases, undertake an operation known as "core aeration." This task is usually done with a machine, known as a "lawn aerator." It would not make sense for the average homeowner to buy such a machine, as it would be used only sparingly, so check at your local rental center for this equipment.

Article Sources
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  1. How to Control Thatch in Your Lawn. University of Minnesota Extension