Dethatching Lawn Thatch

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Robert Pavlis

The snow has melted and it’s a tradition; dethatching your lawn. But should you be doing this to your lawn? Read on and you just might save yourself some work.

Dethatching Lawn Thatch
Lawn Thatch – about 1.5″ thick

What is Lawn Thatch?

Thatch is the build up of old grass roots and rhizomes. It is not the result of leaving grass clippings on the lawn. In fact grass clippings left on the lawn will reduce the amount of thatch. As the clippings decompose they also help decompose old roots and rhizomes.

Different grasses produce thatch at different rates. Warm climate grasses such as zoysia, Bermuda and buffalo produce thatch faster and may need to be dethatched more often. Cool season grasses such as bluegrass, fescue and ryegrass produce thatch more slowly.

Some thatch is actually good for grass since it:

  • keeps soil cool
  • slows water loss
  • insulates plant crowns from temperature fluctuation
  • improves tolerance to foot traffic.

Do You Have a Thatch Problem?

Healthy grass has thatch. You only have a problem if the thatch layer gets too thick so that water and air have trouble getting to grass roots.

Soil Science for Gardeners book by Robert Pavlis

A thatch layer that is less than 1/2″ thick, is not a problem. Leave the grass alone.

To measure  the thickness of thatch, poke around the grass until you find the brown layer near the bottom of the grass blade. With your finger or a stick, poke a hole through the brown layer to the top of the soil. Measure the thickness of the thatch.

When is the Right Time to Dethatch?

Dethatching causes a lot of damage to your grass and should be done at a time when the grass is growing so it can fix the damage before the next dormant period.

Warm-season grass can be dethatched in late spring or early summer after it starts to grow. It is best not to do it in the middle or late of summer.

Cool season grasses should be done in early fall (early September in zone 5) since this is the time when grass grows the best.

Dethatching in fall results in fewer weed problems.

Early Spring Dethatching in Snow Country is a Bad Idea

In colder climates it has become a common ritual to dethatch as soon as the snow melts. People seem to want to get outside and do something, but dethatching at this time of year is a terrible idea. Most cool-season grass does not need to be dethatched, in which case you are just damaging the lawn. Secondly, the ground is still very wet in early spring. Walking on it compacts the soil, damaging soil structure, which makes it harder for your grass to grow. Stay off the lawn in spring.

What is the Best Way to Dethatch?

According to the Ohio State University power dethatchers and power rakes work very well. Dethaching attachments for lawn mowers do not work. The best way to reduce thatch down is to perform core aeration. Core aeration also has the benefit of improving soil structure, solving two problems at once. Core aeration in clay soil really only works in spring when the soil is moist. By fall it can be difficult to get the machines to go deep enough to get a good sized plug.

References:

1) Thatch – The Accumulation in Lawns: http://ohioline.osu.edu/hyg-fact/4000/4008.html

2) Photo Source: The Lawn Company

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

46 thoughts on “Dethatching Lawn Thatch”

  1. I loved what you just said about not dethatching your lawn when the snow melts! Very well said.

    Reply
  2. It sounds like you’ve got a knack for this. I was reading your article and it gave me some great insight on how to get rid of thatch in the lawn.
    Thanks,

    Reply
  3. Robert Pavlis, I bought a “dethatcher” that turned out to not actually be a real dethatcher as it only has small tines that do not penetrate or pull up thatch. The good news is that I took samples and I dont have a true thatch problem. I do however seem to have an excess of lawn debris, mostly from old grass clippings just over the thatch/soil. So thick that when you pull it up with your fingers it comes up in weaved pieces about 1/3 inch thick. You cannot even see dirt or thatch through this debis. The “dethatcher” I bought does a good job at pulling most of this thick debris up. Would it be beneficial to do so? I know you’re not a fan of overfeeding, but I have large areas of very thin grass that certainly will not take to over seeding with this debris present. And it hasn’t thickened up with regular watering and feeding. Thanks in advance.

    Reply
    • Are you sure it is debris and not thatch? grass clippings don’t accumulate very much because they decompose quickly – especially is a poor lawn.

      Reply
  4. Its early September in Massachusetts and I have never de-thatched my lawn. It has a lot of thatch and it’s clearly visible. Can I use a power rake now, or wait till spring. I still have 6 weeks of growing in my area?

    Reply
  5. I live in Michigan and I have ALWAYS dethatched in the Spring.
    I have NEVER had a single problem harming the lawn…and I do a deep raking with 2 passes. May not be everyone’s experience, but I like my lawn to breath before the season and absorbing water, sunlight, oxygen and fertilizer for an entire season. By fall, my lawn is the best on the street.

    Reply
  6. I killed off my lawn with roundup. I then power raked and raked/bagged all of the loosened dead grass. I then mowed/scalped my lawn on the lowest setting using the bag to pick up any remaining dead grass. I topped/leveled off the entire lawn with 6 cubic yards of top soil and rolled it out. Would this be enough prep for slit seeding?

    Reply
  7. You stated “Dethaching attachments for lawn mowers do not work”; but can you please tell me why you believe this to be the case?

    Reply

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