Lawn Dethatching: Everything You Need to Know

Excessive thatch can deprive your lawn of nutrients and make fertilizers ineffective. Use these lawn dethatching tips to fix the problems associated with thatch buildup.

What Is Thatch?

Thatch is a mixture of dead and living grass, stems, and roots that form a layer on the top portion of your lawns root system.

Why Is Thatch Bad?

A thick layer of thatch will suffocate your lawns root system and deprive it of water and nutrients. Any attempt to fertilize or water your lawn will be ineffective since the thatch layer acts as a barrier.

What Causes Thatch?

Thatch is caused when your lawns soil can’t breakdown organic matter at the same rate it’s entering your soil.

You have to remember, your lawn, just like a plant, constantly has new leaves, stems, and roots dying back as new ones form. A healthy lawn is able to maintain a balance in which your lawn breaks down the organic matter as it dies back. If that delicate balance gets thrown off, thatch can build up.

To keep that healthy balance, avoid the following:

1. Synthetic fertilizers. Synthetic fertilizers can negatively impact soil structure and actually kill microbes needed to break down thatch. These fertilizers are often quick release and can cause such a quick blast of growth that it can be tough to keep up with the 1/3 rule when mowing your lawn. The 1/3 rule says you should only be cutting off 1/3 of your grass blade when mowing. 

2. Poor aeration and drainage.  Soil needs air to break up thatch.  Poor aeration and drainage prevents air from entering your lawns soil.

3. Too much watering. Watering too frequently will cause a shallow root system.  You want grass roots to grow deep into the soil.  A shallow root system means a weaker lawn which can’t hold up to drought, fungus, or other problems. This will cause grass to die back at a faster rate then you soil can handle.

4. Too little watering. If your lawn is too dry you’re going to get a lot of grass dying back when the heat of the summer kicks in. This high rate of dying grass, stems, and roots will out compete your soils ability to break it down.

5. Poor management of Disease and Stress. If  you get hit with disease you can have a large portion of your grass die off quickly. This can overwhelm the your soils ability to break down the dead grass, causing thatch. The same is true if your lawn is stressed from heat. Having a solid summer lawn care plan will help keep you lawn healthy during times of heat stress.

How to Know If You Have a Thatch Problem?

A little bit of thatch is normal, even healthy up to about a 1/2” thick.  But anything over a 1/2” is bad for your lawn.

You can tell your thatch layer is too thick if your lawn feels spongy or bouncy, or like you’re walking on a thin cushion.  Also, for visual queues look to see if your lawn is looking thin, or not responding to fertilizer treatments.

If you suspect you have a thatch problem, cut out a section of your lawn about 6” wide x 6” long, and 6” deep.  Take a look at the thatch layer too see if it’s more then half an inch.

Types of Lawn Dethatching?

Dethatching warm season grass is very different than cool season grass. Check each method below to see what the right tool for the job is depending on the grass type and severity of the thatch problem: 

1. Manual removal with dethatching rake.  This is a special rake that is specifically designed to dig into the thatch layer of your lawn and pull it out.  These rakes are effective but can add up to a lot of manual labor.  They are best suited for smaller lawns and lawns with a small to medium thatch problem. These should only be used on cool season lawns since they can be to damaging on warm season lawns.

2. Use a tine rake dethatcher.  A tine rake dethatcher is usually mounted to a ride on mower or tractor, but they also have a hand held version that works for smaller lawns.

Tine rake dethatchers  work by using thin metal tines that scrape the surface of your lawn.  This loosens up any dead grass or leaves and can then be sucked up while mowing.

Tine rake dethatchers are great spring cleanup tools, especially the ones that get mounted to your mower or tractor.  They don’t require a lot of labor and it doesn’t take much more time then if you were to just mow your lawn.

Since tine rake dethatchers don’t really get into the true thatch zone of your lawn, they are better suited as a way of preventing thatch buildup or reducing the amount near the surface of your lawn. These are better for cool season lawns and not recommended on warm season lawns since the tines can pull and rip out stolons. 

3. Core aeration.  Core aeration is made possible by the use of a machine called a core aerator.  A core aerator has hollow metal tines that penetrate into your lawns soil.  These hollow tines pull out plugs, or cores of your lawn, creating tons of small holes throughout.

Since the metal tines go deep into the soil, they break up that thatch layer and pull it out.

Also, the increased air flow into the soil allows microbes to break down thatch.  Core aeration is great for preventing thatch problems and fixing small to medium existing thatch problems on both cool season and warm season lawns.

4. Power raking.  A power rake is one of the best pieces of equipment you can either rent, or purchase, to remove thatch. Typically you would rent a gas powered power rake, or you could purchase an electric machine such as a Sun Joe. Sun Joe machines are becoming really popular and are priced very reasonably ($100-$150).

With power raking, metal tines dig into the surface of your lawn and slice through the thatch layer in a horizontal lifting motion. This brings the thatch to the surface and you will need to clean it up after using either a rake, blower, or mower. These are great machines for cool season lawns, but can be damaging to warm season lawns since a lot of warm season lawns have stolons (runners) that spread on the surface of the lawn. The horizontal lifting action of the machine can damage stolons. 

5. Verticutter, or Vertical Mowing. If you have a thatch problem in your warm season grass, especially St. Augustine and Centipede, than a verticutter is the machine you want to rent! It looks very similar to a dethatching machine however the action of the machine is different. Instead of going into your soil and pulling horizontally and up, a verticutter just chops straight down and then back up. This action will chop the stolons (runners) of you warm season grass, but that is far less damaging to the lawn than if you were to rip those stolons with a dethatcher. When using a verticutter, only go over the lawn once, since too much chopping of the stolons can be damaging. Only verticut your warm season lawn when it is actively growing in late spring/early summer. 

6. Liquid Aeration. Liquid aeration is a liquid that you spray over your lawn that provides many benefits. Although it won’t correct serious thatch problems, regular use will help prevent you from having thatch problems in the future. It works by increasing microbial activity which helps break down thatch and loosen soil. It also creates little pores in the soil that help the flow of water, nutrients, and air. This is a great solution for people that don’t want to rent big machines such as power rake dethatchers or core aerators. Air 8 is a fantastic liquid aerator that gets mixed with water and applied to your lawn. Using this regularly is the best way of keeping thatch problems in check before they get out of hand. It’s a really good idea to add this into your lawn program if you have St. Augustine and Centipede grass which grow via stolons on the surface of your lawn. If you were to mechanically dethatch these grass types it could damage them so in these cases regular applications of liquid aeration is recommended.. If you have a thatch problem in your warm season grass, especially St. Augustine and Centipede, than a verticutter is the machine you want to rent! It looks very similar to a dethatching machine however the action of the machine is different. Instead of going into your soil and pulling horizontally and up, a verticutter just chops straight down and then back up. This action will chop the stolons (runners) of you warm season grass, but that is far less damaging to the lawn than if you were to rip those stolons with a dethatcher. When using a verticutter, only go over the lawn once, since too much chopping of the stolons can be damaging. Only verticut your warm season lawn when it is actively growing in late spring/early summer. 

When to Dethatch Lawn?

Dethatching should be done when your lawn is actively growing and not under any environmental stresses such as drought.

For cool season grasses, early fall is best.  Avoid dethatching with power rakes in early spring since the ground is too wet and the grass is still dormant.  This will cause too much damage.

For warm season grasses, late spring/early summer is the best time to dethatch. You have to be careful when dethatching warm season lawns since some warm season grasses such as St. Augustine and Centipede grows via stolons, which are runners that spread through the surface of the lawn. For these lawns,  stick to using a verticutter, and use liquid aeration (Air 8) regularly to prevent thatch problems.

How to Prevent Thatch Buildup?

1. Use slow release fertilizers.  Slow release fertilizers don’t cause rapid growth of vegetation which can cause thatch problems. A lot of slow release fertilizers are created from organic material that help build soil structure and promote microbial activity. Check out some of these recommended fertilizers here: Lawn Program for Extra Green Grass

2. Cut your lawn frequently, and/or bag your clippings.  This will decrease the amount of organic matter your lawns soil has to break down.

3. Core Aerate. Core aeration has many benefits and is great to add to your lawn care program.  If you can’t do it every year then every other year is still a big help.

4. Irrigate deeply, and less frequently. If you have an irrigation system then set a watering schedule that focuses on less watering days, but for a longer watering duration.  Deep watering causes roots to grow deep.  Frequent, shallow watering causes a shallow root system and is more likely to cause thatch problems.

5. Apply liquid aeration. Liquid aeration is a great substitute if you don’t want to go through the labor of core aeration. Air 8 is a great choice for liquid aeration. Liquid aeration creates little pores in your soil and allow in air and nutrients.

6. Increase microbial activity with bio stimulants. Spraying bio stimulants over your lawn has so many benefits and is one of the best ways to improve soil structure.  

How Often Should You Dethatch Your Lawn?

Dethatching using a power rake should only be done if your thatch layer is greater then 1/2”.  Otherwise, stick to tine rake dethatching and the preventative measures to avoid thatch problems.

What to Do After Dethatching?

After dethatching, rake up the newly exposed thatch. Mowing your lawn will also help to clean things up.  Fertilizing at this time is also important.  This will help your lawn recover and get much needed nutrients. Also, immediately after dethatching is a great time to overseed your lawn if you’re looking to fill in bare spots or incorporate new seed since the surface of your lawn will be opened up which creates good seed to soil contact. Overseeding is not mandatory however.

Check Out These Posts Next

Core Aeration and Overseeding

Top Dressing Lawn: Advice and Benefits

Lawn Care Program for Extra Green Grass

Lawn Care Program for Warm Season Grass (2)

Lime Your Lawn: A Complete Guide

Leave Grass Clippings on Lawn or Not?

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