What Causes Thatch To Build Up & How To Stop It

what causes thatch

Thatch is commonly described as the dead grass debris that builds up on a lawn under the leaf canopy but above the soil however this description is lacking.

Dead leaf material is only the tiniest portion of thatch and the easiest to remove. The true thatch layer is usually under the debris layer of old grass clippings and broken-down leaves; it’s actually a layer of fibrous material made up mostly of roots, rhizomes, stems, and in some cases stolons.

When this organic matter dies off to be replaced by new material the old stuff sometimes doesn’t break down fast enough. The decomposers in a lawn need more time to get through these and if the layer builds faster than it decomposes new roots and rhizomes start growing in the layer making it thicker and thick over time.

Here’s a video I made explaining how thatch builds up in more detail:

I’ve always felt that removing thatch is harder than managing it, so I apply a liquid thatch control product called D-Thatch a few times per year which helps the bacterial in my lawn digest the thatch layer a little bit faster than it would otherwise.

Do Dead Grass Clippings Contribute To Thatch Accumulation

The short answer to this is no; grass clippings do not contribute in any significant way to thatch buildup over time. That’s because grass clippings consist of just leaf material which is very easily broken down by the regular micro-biology in your lawn.

Although the dead grass may appear brown and look like mulch it is actually much less of a problem than the woodier parts of grass plants like the stems and roots that actually form a spongy thatch layer.

See the following video for a visual demonstration:

The Cause Of Thatch Buildup Is Preventable

Since dethatching can take its toll on your grasses, it’s best to prevent excessive thatch build-up. You’ll be surprised that what causes thatch to build upon your lawn isn’t anything external. Too much watering, overly mowing, and overly fertilizing your lawn can cause thatch to build up. Water enough, fertilize enough, and mow enough, but don’t go overboard. Too much of anything they say is never good.

Here is how I determine when to dethatch my own lawn and the advice I give clients requesting the service for their yards:

3 Tools for Dethatching Your Yard

There are three preferred tools for dethatching your lawn in the spring or the fall.  Depending on the thickness of the thatch, the results you are seeking, and your budget will determine which tool you should use.

Manual Dethatching Rakes

A manual dethatching rake can be found online or at any nearby garden center.  They are a specialized rake specifically for removing the dead matter from turf grasses.  There are both fixed versions and one’s that can be adjusted to determine how aggressive the action will work in digging into the turf and pulling out the thatch.

To use a manual rake select the area that you want to work and simply push the rake back and forth over the year.  When you are pulling the rake towards you, the thatch is getting released and when you push the rake, back it is coming off the rake. Then using a regular rake you can pick up the debris and throw it away.

If you really need to break the rules around cool season grass and warm season grass dethatching then I suggest going with the manual dethatching rake as it is the least disruptive of the tools for this task.

Power Rakes

A power rake looks like a small lawn mower without the bag, but the underside is very different.  Instead of a large single rotating blade, it is a series of metal flails that rotate around so that they dig into the top layer of the soil.

Power rakes have a level setting similar to your lawn mower to set the height.  I always suggest starting high for your initial pass and then begin to lower the power rake so that it progressively is going deeper and deeper into the thatch.  The optimal setting for power raking will be removing almost all of the dead material and just starting to scratch the surface of the soil.

If the rake is digging into the soil more than just a little bit you will quickly notice deep scars and bare spots.  This is the #1 reason the vast  majority of homeowners are afraid of dethatching their own lawn.  It is very easy to cause severe damage with a power rake.

Eliminate that from happening by taking it slow and start with a high setting and work down.

Vertical Mowers

Vertical mowing also known as verticutting is very effective with very thick thatches as consist of solid mounted blades unlike the flail style in power rakes. They are designed to cut deep into the turf and effective at cutting lateral stems and rhizomes in the grass while dislodging the thatch.

Most homeowners looking to purchase a machine for dethatching will be best served with a power rake.

Things to Consider While Dethatching:

  • Ensure Your Lawn Is Moist Enough: The keyword being “moist” and not wet.
  • Watch Out For Weeds: Be careful not to dethatch if weeds are also germinating, you could have serious weed problems afterward.
  • Use Herbicides: You might want to make use of pre-emergent herbicides after the dethatching process.
  • Watch the Weather: Detaching can be a stressful activity for your lawn. You don’t want to contribute to this. Try to dethatch the lawn on a day when the weather is cool.
  • Mow Your Lawn: Finally, never attempt detaching an overgrown lawn that might cause too much strain for the turfs. Before you begin, make sure you mow your lawn to at least half its regular height.

What to Do After Dethatching

For optimum results, these are basic practices you should carry out after dethatching:

#1. Overseeding

This is something you want to consider after dethatching. It will definitely help in restoring your lawn to its natural, verdant, and lush look.

#2. Test Your Lawn Regularly

To prevent further thatch complications, it’s advisable to test your soil at least every 3 – 4 years. Also, make sure to follow soil test specifications in order to keep the soil nutrients, and pH level at its optimum. Doing this will help in reducing thatch build-up.

#3. Fertilize, Water and Mow Wisely

Make sure to fertilize your lawn based on the recommendation of the soil test. Just don’t over-fertilize, as this can bring you back to square one.

Same with watering and mowing the lawn. You’ll need to do it right to promote growth and prevent thatch problems. Water enough, but don’t over-water the lawn!

#4. Aerate

Aerate! Aerate! Aerate! I can almost not overemphasize this. It’s important to aerate compacted fields, this will help in loosening the soil and foster the growth of the turf root.

Additional Resources

You can learn more about thatch and thatch management through these other articles here on the site:

How To Remove Lawn Thatch
Best Liquid Thatch Removers w/ Comparisons
Reasons Why You Have A Squishy Lawn
Best Season To Dethatch: Spring
Best Corded Electric Dethatchers Compared
Using Thatch In Composting?
Make Your Own DIY Liquid Dethatcher