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How Often Should You Dethatch Your Lawn?

Depositphotos 68677585 XL How Often Should You Dethatch Your Lawn?

Thatch is not just the roof of an English farmhouse. It is the layer of stems, leaves, roots, and dead things accumulating on lawn soil below the tops of growing grass blades.

So, How Often Should You Dethatch Your Lawn?

A thatch layer of more than 1/2″ – 3/4″–when compressed–is not healthy for your grass. Your lawn needs dethatching at that point. Dig out a small plug of grass to check thatch thickness. Plan your dethatching for late spring or early fall–depending on grass type.

Dethatching machines work better for removing thick thatch. You can also use a manual dethatching rake for a thin layer of thatch. Dethatch the entire lawn.

Here you will find the When, Why, and How of dethatching.

Lawn Thatch – Good and Not So Good

A thin layer of thatch protects your grass roots from moisture and temperature fluctuations. Allowing too much thatch to build up leads to problems that will inhibit healthy grass growth.

Good Lawn Thatch 

Thatch is normal in healthy growing lawns. A thin layer–1/2″ or less– is beneficial on lawns. It collects on the ground at the base of the grass stems where it decomposes and adds nitrogen and other nutrients to the soil. 

The thin layer of organic material also helps conserve soil moisture, regulates soil temperature, and promotes overall lawn health. It allows nutrients, air, and water to better penetrate the soil surface.

Note: Many people believe that leaving grass clippings on the lawn increases thatch buildup. Not true according to the University of Massachusetts. Grass clippings actually help encourage microorganisms that improve lawn and soil quality.

Not So Good Lawn Thatch

Thatch that is too thick slows the penetration of air, water, and fertilizer to grass roots. Since water and nutrients are not making it into the soil, grass tries to root in the thatch to get what it needs to survive. Lawns are stressed by poor root structure.

Thick thatch can also host fungi that can cause turf disease. The fungi have access to the roots and with certain moisture and temperature conditions can cause disease and kill weakened grass.

When to Dethatch Your Lawn

Cut out a small piece of grass turf and soil several inches deep. The spongy layer above the soil is thatch. If it measures more than half an inch thick when compressed, you need to plan to dethatch. 

Cool-season grass such as Kentucky Blue Grass–mostly used in northern states–should be dethatched in late summer or early fall. Warm-season grasses like Bermudagrass–found in the southern states–prefers to be dethatched in late spring or early summer. 

Dethatching is usually not part of a yearly lawn maintenance program. Some grasses–like Ryegrass–will easily grow without dethatching for 5 years or longer. Some grasses, locations, and environments tend to produce a lot of thatch. Check every year. Only proceed if necessary.

Note: Do not dethatch your lawn when it is dormant or obviously stressed–such as during a drought. It will be difficult, if not impossible, for it to repair itself. Do not dethatch a wet lawn. Do not remove all of the thatch at once.

3 Ways to Dethatch your Lawn

Although you can hire lawn care professionals to do the job for you, dethatching your lawn is not much tougher than mowing it. (And it is a great excuse to drink beer.)

  • Manual Dethatching Rake. A short heavy tool with strong tines that digs out thatch as it is pulled through the grass. Works great for light thatch or small areas.
  • Power Rakes. Like a lawn mower with vertical blades that reach down to the ground level to pull thatch to the surface of the grass. Ideal for large areas of light thatch. 
  • Vertical Mowers. Also known as verticutters. Slice through both the thatch and a layer of soil. Pulls thatch and grass roots to the top. Ideal–and may even be necessary–for lawns with very thick thatch.

Many home improvement stores, equipment rental outlets, and some garden centers usually have these machines for rent. Saving you the need to buy one.

Note: Dethatching and aerating your lawn cannot be used interchangeably. Both are very useful for improving grass growth. 

Lawn Maintenance After Dethatching

After dethatching, test the soil ph. It should be around 6.5 for a healthy lawn. Soil testers are available for around $20.00–or less. Soil usually turns acidic over time. Add lime to the soil if you need to bring the ph up.

You can aerate your lawn either before or right after applying lime. Aeration removes plugs of soil up to 3″ long providing pathways for water, lime, and fertilizer to get deep into the soil–improving root quality and speeding up decomposition.

Fertilize your lawn shortly after aerating to allow the granules to fall into the holes you made. Water the lawn to get the fertilizer and lime working at rebuilding the grass and roots.

You can topdress your lawn with about 1/8″ of topsoil. Topdressing takes some of the bumpiness out of the lawn and fills in the aeration holes. Do not use peat as a topdressing. It simulates thatch and can cause some of the same problems you are trying to fix.

It is a good idea to overseed your lawn right after dethatching. Not only will you get bald spots taken care of, but you will also be helping the lawn get thicker and fill out. The seed will find it easier to fall down to the soil and germinate with the thatch removed.

Preventing Thatch Buildup

Cut the grass frequently to a height of 2″ – 3″. Leave the short clippings on the lawn. Reduce nitrogen fertilizer. Amend the soil with potassium, phosphorus, and lime as required by a soil nutrient analysis, Remove a soil plug from random locations every year and check the thatch buildup.

End Notes

Check out the University of Massachusetts Extension Turf Program for more detailed information about dethatching.