What Is and Isn’t Thatch?

Lawn mower of blue green colour being used to cut long grass

Let’s begin by addressing what thatch isn’t. Thatch is not created by clippings that are left on the lawn after mowing. In fact, the best thing you can do for your lawn and the environment is to leave the clippings on your lawn. (Of course we’re not suggesting that you leave a pile of thick clippings in any one area). Those clippings are filled with nutrients that can feed your lawn and reduce the need for fertilizer.

So if lawn clippings don’t cause thatch what does?

The major causes of thatch accumulation are lawn care practices that reduce the population of organisms which can otherwise decompose thatch and/or that cause plant material to develop more quickly than the microorganisms can break it down. Think of thatch as a build-up of organic matter that not only discourages growth but has an effect on your lawns health.

What exactly is thatch?

Thatch accumulates in the soil just below the grass line. It can best be described as a tightly intermingled layer of living and dead stems, leaves and roots which accumulates between the layer of actively-growing grass and the soil underneath. Thatch is a normal component of an actively growing turfgrass. It’s necessary to have some thatch because it increases the resilience of turfgrass to heavy traffic. But like so many other things; too much of it can have negative consequences on the health of your lawn.

What does thatch do to my lawn?

An excessive thatch layer (more than 1 inch) can restrict the movement of air, water, fertilizer and other materials from reaching the roots of your lawn. This restriction of air, water and nutrients causes the grass to take root within the thatch layer itself so it can get air and water. This not only reduces your lawn’s drought resistance, if the thatch dries out it can’t take in irrigation easily. Even if the thatch stays moist, it can harbor fungi which can cause turfgrass diseases. If the thatch problem is serious, and if temperature and moisture conditions are right, disease can kill off a lawn that is already weakened by stress. The negative consequences of adverse weather conditions and the likelihood of injury from pests are increased as a result of a thick layer of thatch.

How do I know if I have a thatch problem?

To determine if your lawn has a thatch problem, cut out a small, triangular-shaped plug of turf several inches deep and take a look at it. You will see a spongy layer of material above the mineral soil. If this layer is more than ¾ to 1 inch thick when you compress it, you should consider having your lawn dethatched or beginning a management program which will encourage thatch decomposition.

What can I do if I have a thatch problem?

Research has shown that earthworm and microorganism activity play a vital role in preventing excess thatch accumulation, but there are other steps you can take to address the problem. Core aeration when the turf is actively growing reduces thatch build up. Should the thatch accumulate to an excessive thickness (over 1 inch), it is recommended that you consider de-thatching your lawn.

De-thatching, the vigorous raking or verticutting of your lawn to reduce thatch, will allow air and water to penetrate into the root zone of the grass. Dethatching machines, sometimes called vertical mowers, verticutters, power rakes or dethatchers have vertically spinning blades which pull some of the material to the surface as they slice through the thatch layer. Most equipment rental outlets have dethatching machines.

Mechanical dethatching should be done when cool weather prevails and the soil is not wet. Other5 maintenance practices which discourage thatch build-up are frequent mowing’s to maintain the grass at a reasonable height, keeping clippings on the lawn, reducing nitrogen fertilization and amending the soil with phosphorus, potassium, and lime according to a soil nutrient analysis.