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Dethatching Lawn Thatch

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.

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 is tough on your grass and you should time it so that the grass has sufficient time after the operation to regrow and repair the damage done by dethatching.

Warm season grasses can be dethatched in spring or fall. It is best not to do it in the middle of summer.

Cool season grasses should be done in early fall (late August or 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 the north, 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. First of all, most northern grass does not need to be dethatched, in which case you are just damaging the grass plants. 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 p0wer rakes work very well. Dethaching attachments for lawn mowers do not work. The best way to keep thatch down is to perform core aeration. Core aeration also has the benefit of improving soil structure–you solve two problems at once. In clay soil core aeration 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

Robert Pavlis
Editor of GardenMyths.com
I live in southern Ontario, Canada, zone 5 and have been gardening a long time. 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!

I hope you find Garden Myths an educational site that helps you understand your garden better.

28 Responses to 'Dethatching Lawn Thatch'

  1. mighty green says:

    In the South is it okay to dethatch in early spring? We get a little snow but not much.

  2. Joann Anderson says:

    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!!!!!

  3. John sergeant says:

    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

  4. Sherry says:

    Can dethatching be done with a garden rake or leaf rake or do I have to buy a thatching rake?

    • 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.

  5. Jeff says:

    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

  6. Jeff Duval says:

    Hi…. I live in the Norteast,NH, and have always gone back and forth on spring thatching…. your thoughts?

    • If you have too much thatch, spring is a good time to dethatch.

      • sally blanton says:

        get rid of the grass lawn…it is useless, consumes chemicals and energy and is nothing more than a status symbol

        • 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.

  7. Dawn says:

    Would a mushy lawn indicate a thatch problem.

  8. Chris Chianelli, Bath, Ontario, Canada says:

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

    • 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.

  9. Robert says:

    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.

    • 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.

  10. Norm says:

    Wanting to know hoe often to thatch once a year or every 10 yrs. 2 times a year ?

  11. Tyler Slade says:

    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.

  12. 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?

    • Robert Pavlis says:

      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.

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