Thatch and Your Lawn
What is thatch?
According to Peter Landschoot, Ph.D., “Thatch is a loose, intermingled organic layer of dead and living shoots, stems, and roots that develops between the zone of green vegetation and the soil surface. Those parts of grass plants that are the most resistant to decay — stem nodes, crowns, fibers of vascular tissues, and roots — make up the bulk of thatch.”
You can tell that your lawn has too much thatch if it has a spongy feel when you step on it.
If it does, cut out a sample of the lawn. If more than a ½ inch is made of spongy material, then you have too much thatch.
Tip: You are more likely to have thatch if your lawn is made of Bluegrass.
Why is excess thatch bad for my lawn?
While a little bit of thatch benefits your lawn, too much can have a stifling impact.
Excess thatch can:
harbor damaging insects.
cause mower scalping (because the wheels sink deep into the thatch and lower the blades).
prevent air, water, fertilizer, and pre-emergents from reaching the soil.
What causes thatch?
Thatch accumulates when the soil lacks organisms that decompose it. Your soil probably lacks these organisms if:
The soil is too acidic.
This means the soil has a pH of 5.5 or lower.
The soil structure and composition is bad.
Typically this means the soil is compact or has too much clay or sand.
The soil has too many pesticides.
Heavy use of pesticides harms earthworms and several microorganisms. If earthworms are not healthy and abundant, they don’t perform their functions that decompose the thatch.
The soil has too much fertilizer.
Heavy use of fertilizer causes stem tissues to grow too quickly. It can also acidify the soil.
Should I keep grass clippings on my lawn?
A moderate amount of thatch can actually help your lawn because the microorganisms in your soil digest the clippings easily. Therefore, leaving your grass clippings on a healthy lawn typically causes no problems. However, you should not leave grass clippings on your lawn if you have a layer of thatch more than ½ inch thick.
The clippings offer several benefits. They:
return nutrients to the soil.
retain moisture.
reduce water evaporation.
insulate the grass from extreme temperatures.
prevent weed seeds from reaching the soil.
prevent weeds from growing.
soften the impact of foot traffic.
How Can I Prevent Thatch Buildup?
Don’t wait for thatch to build up. You’ll need to work actively to prevent it from getting out of hand.
To prevent thatch buildup, you can:
Minimize your use of fungicides and insecticides.
Limit your use of nitrogen.
Aerate your soil.
Mix perennial rye grass with aggressive thatch makers like Bluegrass.
Test your soil’s pH level periodically.
How can I get rid of thatch?
To get rid of thatch, simply work it out with a garden rake. If your property is large or the thatch level is thicker than an inch, you can go over the lawn with a dethatcher or power raker. Dethatchers are damaging to living grass, so you should avoid doing this when the grass is vulnerable. For example, your grass is particularly vulnerable when the temperature is extreme, the snow has barely melted away, or you have recently planted seeds. If possible, avoid dethatching in the spring since it can bring weed seeds closer to the surface and allow them to grow in the summer.