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What is lawn thatch and how to control it?

Posted by Jack on Mar 26, 2016 8:53:25 AM

What is thatch?

Thatch is a layer of dead and decomposing plant material between the blades of grass and the soil surface.  It is composed of grass clippings, dead plant material, and other debris that slowly decompose.

lawn_thatch.png

What are the pros and cons of thatch buildup?

It is good to have a thin (1/2" to 3/4" inch) layer of thatch.  This serves several purposes:

  • A thin thatch layer will help to insulate the grass roots from cold temperatures.  This is especially helpful for Zoysia and Bermuda Grass grown in the Maryland area.
  • The thatch will also help to retain soil moisture, just like mulch would in a flower bed.  This means that the soil will not dry out as quickly between rainfall.
  • Some thatch will provide a "cushion" making the surface better for athletic uses.  The thatch will also slightly increase the durability of the lawn under high traffic conditions

That being said, there are many cons to having too much thatch:

  • Thatch can provide an excellent ecosystem for both fungus and insects that feed on your lawn.  
  • Thick thatch layers can cause the roots of your lawn to actually grow in the thatch layer instead of the dirt below it.  This will cause the roots to dry out faster between waterings
  • Thatch can cause mower scalping.  The wheels of the mower may sink into the soft thatch layer and cause the mower blades to slice into the crown (base) of your lawn grasses.  This is not good for the grass!

How can I properly manage thatch buildup?

  • First, determine the thatch buildup potential for yourturfgrass species.  This is the biggest factor for determining how much work you will have to do to control the thatch.
    TurfGrass Thatch Potential
    Tall Fescue Low-Medium
    Kentucky Bluegrass Medium - High
    Zoysia High
    Bermuda High
  • Soil acidity:  Ensure that your soil is not too acidic by testing its pH.  Acidic soils will a pH below 6 will have less beneficial microbes that actively decompose thatch.  Raise soil pH by regularly liming the area.  Click to buy online
  • Do not consistently over apply fertilizer.  Constantly over applying fertilizer will encourage grass to grow rapidly.  Over time, the clippings will build up into a thick thatch layer and will not decompose as quickly as they are produced
  • If you have an inch of more of thatch, you need to use an aerator or slit seeder in the spring or fall to physically disturb the thatch layer.  These machines have blades that cut into the thatch and help it to decompose.  Be sure to use several passes!  The lawn should look somewhat "torn up" when you are finished but it will recover quickly.  If you have a Zoysia or Bermuda lawn, you should do this in May.

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