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, source: The Lawn Company

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.

Microbe 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 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.

Building Natural Ponds book, by Robert Pavlis

Growing Great Lawns

Here are some other articles about your lawn.

The Truth About Clover in the Lawn

Biological Liquid Dethatcher for Lawns – Do They Work?

How to Get Rid of Moss in Lawns

Lawns Reduce CO2 Levels

How To Add The Right Clover To Your Lawn

Does Liquid Lawn Aeration Work – Liquid Soil Conditioners?

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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 would like to thach my yard in the spring, should I do the fall fertilize thing? I’m in the northwest (Seattle) area. I didn’t fertilize last spring or fall . So the grass is not so good. Lots of moss. And dead spots.

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  2. I’m in the south and my lawn looks so brown with a lot of dead grass. I have irrigation and I feel like the dead grass needs to be raked out. Will it kill my grass if I do it in mid summer?

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  3. Thank you for all the answers you’ve provided here. I had sod put down 3 years ago on my new property here in Connecticut. It seems very temperamental reacts to hot dry conditions fast. I enjoyed keeping it longer like 4 to 5 inches but I think alot of the roots are growing on top of the soil. If I rake thatch out aggressively with a rake it seems to kill the grass. I tested an area off to the side that is predominantly more wet then my other areas. I can end up taking out a large amount of thatch but then it seems I’m only left with a little bit of the grass that actually has roots in the ground. I will aerate the lawn this month and hopefully when I spread some seeds some will land in Holes and grow like they should from the ground not on top of. I decided to cut my lawn shorter down to 2.5 inches but ended up having developed a bunch of brown spots.

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  4. Omg I need help!!!! I had my yard dethached and it just died I live in Colorado Springs Colorado!!! Do you think I killed my yard ??? I don’t know what to do ???? I’m at a lost I’ve never seen this kind of brown spots that looks dead !!! I feel like if I didn’t dethached I wouldn’t if had this problem!!!! I’m in trouble please please help!!!!!

    Reply
    • You will need to find someone local to have a look at the lawn. Dethatching, if done properly, will not kill the grass.

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  5. I live in northern I’ll and just power raked my lawn with a machine it’s late April and I overseeded it will my lawn heal with warm weather coming

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    • Rakes don’t dethatch very well. You really need to cut through the thatch with sharp blades. I recommend a professional machine for this, which you can probably rent, or have done professionally.

      Reply
    • I just bought a “SunJoe” dethatcher and it worked GREAT!!!
      Only About $125, and it’s lite and easy to work with.
      Check out their website…you won’t be disappointed!!!

      Reply
  6. I dethstched and mowed short this week in spots lawn looks very brown. Should I seed? I Am in South Dakota. My wife thinks the lawn is dead there is much green but a lot of brown down low

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        • It is not useless – it provides an important aesthetic feature for gardens and is the best plant for making walking areas.

          If everyone was a gardener – then we could get rid of the lawn – but they are not. I have been looking at lawn alternatives and have yet to find one that meets the requirements provided by a lawn and takes less chemicals to control. It is a common battle cry from environmentalists – but they have not provided an alternative.

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  7. we have had a drought and it has killed some lawns. Should the remaining lawn be dethatched at this time of year?

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    • Dethatching has nothing to do with climate or dead lawns. How much thatch do you have? If you have too much then you should dethatch.

      Early fall is a good time to dethatch so the grass roots can heal themselves in the coming cool months.

      Reply
  8. I have small leaves and flower pedals that collect in my lawn. Can I seed over it or do I need to de thatch before seeding. Not sure if the seed will reach the soul.

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    • Will seed that falls onto leaves germinate? Probably not, and if it does it won’t grow. If you are going to over seed you need to remove the leaves.

      But this has nothing to do with dethatching. You don’t have to dethatch in order to over seed.

      Consider this – most over seeding does not work. Unless the seed reaches the soil, and is covered with a bit of soil it will probably not grow. Seed bigger patches where you can rake seed into the soil, but forget over seeding the whole lawn.

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    • When it needs it. If it gets more than 1/2 inch you should dethatch. If it never gets more than this – you never dethatch.

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  9. At first we have to decide that if the lawn needs dethatching or not. And if you think that lawn needs dethatching than it should be done in the early days of the corresponding season. If it is done during cool season than it will be done during early spring. If the lawns are big than power dethatcher is being used that covers the lawn area once.

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  10. Another reason, I think, to avoid spring dethatching is that very moist soils (like we have right now in Vermont with the snow melt) don’t hold the plants very strongly. So if you try to dethatch, you will pull lots of grass plants up out of the ground.

    Robert, is there evidence about how tall grass is allowed to grow and how that correlates to build up of thatch? I.e., can I reduce or slow the build up of thatch by allowing my lawn to grow relatively taller, or mowing it relatively shorter, or does that not matter, or does it matter but only sometimes depending on the species of grass?

    Reply
    • Good comment about pulling grass out this time of year.

      Does mowing height affect thatch? I could find no reference to indicate that longer grass would increase or decrease the amount of thatch. When grass grows better, it does form more thatch. For example, if you fertilize you will make the grass grow better, which in turn increases the amount of rhizomes and roots, which in turn increases the thatch. Mowing higher does make the lawn grow better, so I suspect it will also increase thatch. But I suspect the benefits of longer grass outweigh the downside of more thatch.

      Reply

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