The worst effects of this summer’s drought seems to be over. It’s amazing to see our lawns green up after suffering from one of the worst droughts in our state’s history.

But not all lawns survived the drought. Many lawns burdened with thick layers of thatch died.

Do you have too much thatch in your lawn? Now is a good time to check.

If discover you have too much thatch, now is the best time of year to fix the problem.

What is thatch?

Thatch is a layer of roots, shoots and stems, both living and dead. This brown, matted layer develops between the green vegetation and the topsoil.

How does thatch develop?

Your lawn is a living system. It grows organic matter (grass plants) while at the same time decomposes organic matter. When your lawn produces more organic matter than what it can decompose, you get thatch.

How much thatch should I have?

A little thatch is good. It insulates the lawn from extreme temperatures and extreme moisture conditions. Thatch makes the lawn more resilient and provides good footing.

When thatch exceeds one inch in thickness, it is bad. It can become a barrier that prevents the roots from getting the air and water it needs from the soil.

How do I measure thatch?

Cut a wedge out of your turf. Pretend like you are cutting a piece of pie and go down, 2 inches into the soil. Pull out the wedge. Thatch is the brown mat between the grass blades and the topsoil.

What causes excessive thatch?

Too much fertilizer, pesticides and water on the lawn create thatch.  

Aggressive fertilization will create a lot of plant growth, in fact, too much growth for the microbes in the soil to decompose.

The excessive use of pesticides will kill soil microbes and earthworms that help to decompose thatch. Excessive irrigation will drown and kill soil microbes.  

Do grass clippings create thatch?

Not if the lawn is mowed regularly. Avoid removing more than one-third of the grass blade at any one time. For example, if your turf is maintained at 3 inches, mow the turf when it is 1.5 inches tall. Use a mulching mower.

Young grass blades are almost all water, and they will decompose readily.

The problem is when you mow irregularly. Older, taller grass blades will get fibrous and decompose more slowly.  

How can I prevent thatch?

Limit your fertilization to only what is needed. This is subjective, but the more you fertilize, the greater your risk of thatch build-up. The most beneficial time to fertilize your lawn this year is right now.

Core aeration is a good preventative activity. Aeration stimulates thatch-decomposing microbial activity in the soil. Aeration will physically remove thatch, too.

Limit your use of pesticides. Rarely does a lawn ever need a fungicide or insecticide application. Minimize your use of herbicides; use spot sprays. Mid- to late September is the most effective, and in many cases the only necessary, time to spray.

What if I have too much thatch?

Dethatching is recommended if your thatch is one inch or thicker.

Dethatching is a destructive process. It should be done when the turf grows actively and can recover quickly. Early to mid-September is a great time.

You can remove thatch using a vertical mower. These are available at rental dealers, garden centers and hardware stores. Dethatching is also done by lawn care services.

Set the tines at a depth where they rake the thatch but cause minimal damage to the soil.

Rake up the debris with a leaf rake. This debris may be composted. Irrigate the lawn to activate the healing and growth of the lawn.

You may aerate, overseed and fertilize the lawn after dethatching. Use a A light, half-strength fertilization. Your lawn will recover in a few weeks.

Written by Tom Kalb, Extension Horticulturist, North Dakota State University. Photos courtesy of Kansas State University Turf and Landscape Blog and Tom Kalb. 

Sources:

Bauer, S. 2018. How to control thatch in your lawn. University of Minnesota Extension.

Landschoot, P. 2020. Managing thatch in lawns. Penn State Extension.