Ripping, tearing, slicing, slitting, cutting — all sound like unpleasant things to do to a perfectly innocent lawn. But if you have a dense underlayer of thatch keeping your lawn from doing its best, your lawn will benefit from dethatching. If you want to know when and how to dethatch your lawn, you’re in the right place.
Warm-season lawns should be dethatched in late spring or early summer, and cool-season turfs in late summer or early fall. But your lawn will give you signs that it needs dethatching, which we discuss in this article. We’ll also explain what thatch is, how it develops, and how to keep it from returning.
Dethatching is something you can do yourself; you will need a dethatcher (which you can either buy or rent) and the instructions we provide in this article. Keep reading to find everything you need to know about how to dethatch your lawn.
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What Is Thatch?
Thatch is a tightly intermingled layer of dead and living grass shoots, stems, and roots that accumulate above the soil and below the green vegetation.
A bit of thatch is normal and even beneficial:
- It gives turf a bit of a bounce, beneficial for little feet and golf balls.
- A thin layer makes grass more resilient against wear.
- It insulates soil and grass roots against temperature extremes.
Lawn thatch develops when the organic matter in grass produces more quickly than it decomposes. While a rapidly growing lawn sounds great, excessive thatch buildup causes soil compaction and leads to several problems:
- Disease-causing fungi and insects are inside.
- It holds on to humidity, which promotes disease.
- It limits root growth, resulting in a shallow system of grass roots.
- Movement of air, water, and nutrients in the soil is slowed.
|How Do You Measure Thatch?|
|1. Take a trowel.|
2. Dig out a two-inch deep piece from the lawn.
3. Measure the brown spongy material between the dirt and the green vegetation.
4. Cut several plugs, to be sure.
5. A thatch layer greater than 1/2 inch is too much thatch.
When to Dethatch a Lawn
Now let’s talk about when you should dethatch your lawn. The best time to dethatch your lawn depends on the type of grass. Dethatch warm-season grasses in the late spring, or you can dethatch in early summer as well. Dethatch cool-season grasses in the late summer or early fall.
These times correspond with their annual growth spurts and favor rapid recovery. That means three or four weeks of good growing weather (at least) after dethatching.
Which grass type do you have? Cool-season lawns are most often grown by homeowners in the upper U.S. Warm-season grasses thrive in warmer regions, such as in the South and along more southern or coastal areas.
Cool-season lawn grasses:
- Fine fescues
- Kentucky bluegrass
- Perennial ryegrass
- Tall fescue
Warm-season lawn grasses:
- St. Augustinegrass
How Often Should You Dethatch Your Lawn?
A good rule of thumb is to dethatch your home lawn yearly. But there are other factors that play a role in how often to dethatch a lawn:
- The grass type: Some turfgrass species can build thatch more quickly than others. Bentgrass, Bermudagrass, and Kentucky bluegrass create more thatch and must be dethatched yearly.
Perennial ryegrass and tall fescue, on the other hand, produce less thatch and can wait longer to be dethatched. In their case, pay attention to the signs of thatch accumulation to know when is the best time to dethatch your lawn.
- Maintenance routine: Grasses that are overfertilized and overwatered create more thatch.
- Soil condition: Heavy, poorly drained, or clay soils may cause the grass to accumulate thatch more quickly.
How to Dethatch a Lawn
- Dethatch with moist soil but not wet. Water thoroughly two days before you plan to bring out the big guns.
- Run the dethatching machine three times at least, and in different directions each time, advises Don Callahan with the Yamhill County Extension in Oregon.
- The machine should churn up roughly the same volume of plant material each pass, he says.
- Remove the piles of thatch right after dethatching.
- Overseed the lawn. The time is right to get some fresh seed and new turfgrass into your lawn, Callahan says.
- Consider topdressing. It can give the existing root system a boost. Topdressing can also be a form of weed control, filling those gaps before weeds have a chance to take hold.
- Wait a month. Then you should see some results, Callahan says.
Signs Your Lawn Needs Dethatching
These are the signs of compacted soil and a lawn that needs dethatching:
- The thatch is a half-inch or more
- A bouncy or spongy feel when you walk on it
- Dry spots, which appear when water isn’t making it through the thatch
- Footprinting (footprints take more than an hour to go away)
- Diseases (the grass is more vulnerable)
- Insect problems (because the grass isn’t healthy)
- Decreased hardiness (shows greater distress in heat or cold)
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Common Causes of Thatch
People used to think thatch comes from grass clippings, Don Callahan explains. But thick thatch is a result of other things:
- Dead leaves decaying along with stems and roots
- Roots growing in the thatch but not reaching the soil under it
- Lateral shoot growth (aka stolons and rhizomes), something that can happen when thatch interferes with roots trying to grow down
- Infrequent mowing: Lawns should be mowed weekly during the growing season, or, if you want to keep measuring, check out a full list of proper mowing heights for each grass.
- Taking off too much at once: You want to follow the one-third rule or mowing, which says to remove up to one-third of the height of the grass (but no more!) per mow. Taking off too much at once places stress on the grass and can weaken it and slow its recovery time. If your lawn is too tall, take down the height over several mows.
- Excessive water: Giving the lawn too much water or having wet soil (often caused by drainage problems)
- Dry soils, when it is chronic or when the thatch is keeping water from getting through
- Pesticides used on a regular basis, not as needed. Plus, they can kill earthworms, which stimulate the breakdown of thatch.
- The type of grass matters: Some turfgrass species produce a lot of stem tissue: Cool-season grasses to watch include Kentucky bluegrass, creeping bentgrass, and creeping red fescue. Conversely, perennial ryegrass and tall fescue do not produce significant thatch buildup.
If you have a warm-season lawn, these grasses are prone to excess thatch: Bermudagrass, centipedegrass, St. Augustinegrass, Zoysiagrass.
Prevent Thatch Buildup From Returning
The picture above shows lawn thatch before and after the dethatching process. But another crucial matter is what to do after dethatching your lawn to prevent buildup from returning. Here’s how you can go about this:
- Fertilize the lawn. Fertilize only enough to maintain your lawn’s desired color and growth. For cool-season lawns, fertilizing in fall (September) or late fall (through December) is better than spring fertilization because the grass stores carbohydrates more efficiently and grows stronger roots.
- Aerate the soil. You want proper drainage. Fertilize right after you aerate.
- Mow properly. Trim no more than one-third of the height of the grass. Leave the grass clippings; they decompose rapidly, recycling nutrients back into the lawn.
- Avoid pesticides unless they are necessary. Then use them for a specific reason, deciding on a specific type, for a specific length of time.
- Test your soil periodically for its nutrient levels and acidity. If you are concerned about over-fertilizing (which can cause overproduction of thatch) or want to manage pH, a soil test is the way to go. Contact your local Extension service to test your soil and only fertilize if needed.
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Dethatching Tools: A Guide
Dethatching machines come in various forms. Although some lawn services and rental companies use the terms interchangeably, the machines perform dethatching by different means, with varying levels of intensity.
What they have in common are spinning metal pieces that pierce and lift the thatch from the lawn. Some employ slicers, others metal tines (experts recommend the former as more effective). Some are stand-alone, powered units, others are made to be dragged behind a tractor or riding mower.
Here are some of the most common dethatching techniques, and the power dethatchers that perform them.
|Core Aerator||Aeration is an option for lawns with a mild amount of thatch. A core aerator will pull up plugs of sod and soil, which can provide space for nutrients and grass roots to penetrate beneath the thatch layer. However, you can’t aerate to remove large volumes of thatch.|
|Power Rakes||Power rakes attack serious thatch. Using a power rake carries some risk to the lawn since they can pull up live plants along with dead grass. They come with adjustable flail blades that allow deep penetration into the lawn.|
|Slit Seeders||These are all-in-one machines owned by some professional lawn care companies. They have one set of spinning blades that dethatch, then another set of circular blades that lay down grooves. They can have tines. They dethatch and plant grass seed in a single pass. These machines will lift a large volume of thatch — even on small lawns, it can produce enough to fill several lawn bags — that needs to be gathered up with a rake or lawn mower with the mulching unit attached.|
|Sod Cutter||These machines are for the most-serious thatch problems — 1 inch or more. They have thick blades that cut through to the soil surface and allow you to remove sod in strips. You need to completely renovate the lawn if using a sod cutter.|
|Vertical Slicer||Vertical slicer, vertical mower, or verticutting machines slice through the lawn to pull up thatch. Often used on sports fields, set the vertical lawn mower low enough to leave some soil on the surface of your lawn. It should cut about a quarter-inch into the soil after the grass blades have gone all the way through the thatch layer. Hand rake loose thatch after slicing, leaving the soil layer as topdressing.|
How Much Dethatching Costs
Professional dethatching services cost around $190 per hour or $0.35 to $0.15 per square foot.
The cost to rent machines:
- Simple, motorized dethatching machines can run from the low $100s to nearly $300.
- Tow-behind dethatchers can vary widely, from about $70 to almost $3,000, depending on the size and features.
- Nonmotorized options can run as low as $35 for a simple thatching rake. A gas-powered version can be rented starting around $50.
- Slicing dethatchers come in a wide variety of options. One option is an attachment that fits on a regular walk-behind tiller, which runs about $80. Push, walk-behind, and tow-behind options can range from as low as $39 to more than $350.
- Rental options are available for slicers, too, with prices in the ballpark of $110 per day.
DIY? Or Call in a Lawn Care Pro?
If slicing up that turf you’ve worked so hard on makes you more than a little nervous, it’s best to leave it in the hands of a professional lawn care service. In addition, the service has experience using the equipment and has every piece that might be needed.
If you can handle a walk-behind lawn mower, you can handle a dethatching machine, Callahan says. And a dethatching machine is what is needed, he adds. Dethatching an entire lawn by hand is a “horrendous job and not effective,” Callahan says. If you are going to dethatch the lawn yourself, get a rake; you will need it for the cleanup.
Can Grass Clippings Cause Thatch?
Despite popular belief, short clippings dropped on the lawn as mulch after mowing are not the cause of thatch buildup. Grass clippings are very high in water content and break down rapidly when returned to lawns after mowing, assuming lawns are mowed on a regular basis (not removing more than one-third of the leaf blade).
What Is the Difference Between Dethatching and Aerating a Lawn?
Dethatching removes the organic matter that impedes the flow of nutrients. Aeration removes cores of soil, something that relieves soil that has become compacted and gives roots space to grow. Aeration will remove small amounts of thatch.
Are There Times When You Shouldn’t Dethatch?
Dethatching should not be done during periods of high temperatures, drought, or during late fall when winter is near. It’s best to dethatch at the beginning of the grass’s period of active growth to maintain a healthy lawn.
In Terms of Dethatching, What Is a Good Soil pH?
A soil pH between 6.0 and 7.0 will favor microbial activity and breakdown of thatch.
When to Call a Lawn Care Pro
Don’t wait for your lawn to start losing its color or the grass to start dying to take action. Take a trowel and check how much thatch you have. If you have a thick layer of thatch, contact a local lawn care pro to take this destructive, but necessary, chore off your lawn care to-do list.
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