Ripping, tearing, slicing, slitting, cutting — all sound like unpleasant things to do to a perfectly innocent lawn.
Dethatching, however, requires actions that sound violent — and kind of are. But if you have a dense underlayer of thatch keeping your lawn from doing its best, they’re serious but necessary actions.
Master gardener Don Callahan with the Yamhill County Extension in Oregon, says it’s something most homeowners can tackle themselves.
So here’s what thatch is, how it develops, how to free your yard from it and keep it from returning.
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 little 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 also makes grass more resilient against wear and insulates soil against temperature extremes.
Problems with a thick layer of thatch vary largely due to the type of grass, Callahan explained. For some, it’s virtually never a problem, but some build up thatch quickly. That’s especially true for lawns that are already struggling.
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 leads to several problems:
- It harbors disease-causing fungi and insects.
- It also holds on to humidity, which promotes disease. I
- It limits root growth and the movement of air, water and nutrients in the soil.
People used to think thatch comes from lawn clippings, Callahan said. But thick thatch is a buildup of other grass components: roots, rhizomes, stolons and dead leaves.
Common Causes of Thatch
If your lawn has an unruly, excessive layer of thatch, it usually comes from a few things.
- First, a lack of earthworms in the lawn’s soil. As the worms burrow, they boost the oxygen in the soil and promote the breakdown of organic material.
- Too much acidity is a second common cause, according to the University of Kentucky Extension Service. Microorganisms healthy to your lawn do their best work in a neutral pH range, between 6.0 and 8.0. Adding lime is a common solution to acidity problems.
- The third is too much fertilization. Applying high rates of nitrogen year in and year out lead to excessive growth that natural breakdown can’t keep up with. Some nitrogen sources can even increase soil acidity and lead your lawn back to the second common problem.
- Poor aeration. Grass roots need space to grow, and a highly compacted soil prevents the roots from reaching down deeply.
Kentucky bluegrass is the last common cause. It grows underground stems that take longer to break down.
Once the layer builds up to between one-half and one inch, it stops being helpful and starts to cause a number of problems.
Too much thatch can reduce fertilizer or pesticide effectiveness and give fertile ground to insects or diseases.
Your grass can also eventually start to spread its roots through the thatch instead of the soil. Thatch won’t hold water well, leaving that grass vulnerable to cold, heat and drought stress.
Signs Your Lawn Needs Dethatching
So how to break up that dense layer of thatch without ripping your lawn to shreds? And how do you know when you need to?
You must dig down in your lawn and see what you have. With a trowel or other tool, dig out several patches. If you see a half-inch or more, consider dethatching.
Your lawn will likely exhibit other symptoms if it needs dethatching.
Signs of excess thatch include:
- Dry spots.
- Increased disease.
- Increased insect problems.
- Decreased hardiness; shows greater distress in heat or cold.
Don’t remove thatch when the turf is weak or under stress, warns the Penn State Extension. That increases the chance you’ll injure the turf and decreases chances for its healthy recovery.
When to Dethatch
When to dethatch depends on whether you have cool-season grasses or warm-season grasses. The two types of grasses have different growth patterns. You want to dethatch when they’re in active growth spurts.
- Cool-season grasses, such as Kentucky bluegrass, can be dethatched in the spring, or late summer spring and early fall, matching their most-active growth seasons.
- Warm-season grasses, including Zoysia, Bermuda and St. Augustinegrass, should be dethatched in summer, again, when they’re growing most.
Preparing to Dethatch
Lawns should be dethatched only when conditions favor rapid recovery. That means three or four weeks of good growing weather after the dethatching.
Dethatch with moist soil but not wet. The Virginia Extension recommends watering thoroughly two days before you plan to bring out the big guns.
Run the dethatching machine over your yard at least three times, Callahan said, in different directions each time.
The machine should churn up roughly the same volume of material each pass, he said. Then collect and remove all the thatch.
Dethatching Machines, Tools, Techniques
Dethatching machines come in various forms. And although some lawn services and rental companies use the terms interchangeably, the machines perform dethatching by different means, with varying levels of intensity.
Here are some of the most common dethatching techniques, and the power dethatchers that perform them. 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.
As the name implies, these machines slice through the lawn to pull up thatch. Often used on sports fields. Iowa State University’s Horticulture Guide recommends setting the vertical mower low enough to leave some soil on the surface of your lawn. It should cut about a quarter-inch into the soil after it’s gone all the way through the thatch layer.
Hand rake loose thatch after slicing, leaving the soil layer as topdressing.
Power rakes attack serious thatch. Using them 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.
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 dethatch and plant grass seed in a single pass.
In any case, passing over the lawn with any of the above dethatching machine 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 mower with the mulching unit attached.
Reserve these machines 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.
Aeration is also an option for lawns with a mild amount of thatch. A core aerator will pull up plugs of sod, which can provide space for nutrients to penetrate beneath the thatch layer. However, you can’t aerate to remove large volumes of thatch.
How Much Dethatching Costs
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 its size and features.
Nonmotorized options can run as low as $35 for a simple thatching rake. A gas-powered version can be rented from around $50.
Slicing dethatchers, like other options, come in a wide variety. 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.
But if you can handle a walk-behind mower, you can handle a dethatching machine, Callahan said.
And a dethatching machine is the way to go. A simple leaf rake won’t do the trick. Dethatching an entire lawn by hand is a “horrendous job and not effective,” Callahan said. He recommends renting equipment to save yourself plenty of time and sore muscles. It’s not a highly technical process either, he added.
There is one valuable advantage of a professional lawn service, though. That’s the effectiveness of a practiced hand and expensive equipment afforded by an economy of scale.
Cleaning Up, Reseeding After Dethatching
Whether you do it yourself or hire a professional, it’s a disruptive process to say the least, and your lawn is going to need a Band-Aid and some time to heal.
The first thing to do after dethatching is to remove the piles of thatch from your yard.
After dethatching, seed the lawn and consider topdressing. If you’ve taken plugs of soil, that soil can be left as a topdressing. But the planty thatch material should be removed.
Callahan said the new areas opened by dethatching are a good opportunity to get some fresh seed and new turfgrass into your lawn.
Topdressing, he said, could give the existing root system a boost. It can also be a form of weed control, filling those gaps before weeds have a chance to take hold.
Within a month, you should see some results, Callahan said, depending on the weather.
Hot, dry weather could slow it down, but nice weather will get that new grass coming up uniform and vigorous in about a week, he said. In no time, it will look like a new lawn.
Preventing Thatch Buildup From Returning
Keeping the thatch from building up so fast can keep your lawn looking better longer. It will also keep you from having to rip and tear at it with dangerous machines.
Know that some of the most-popular grass species are the most likely to have thatch. Kentucky bluegrass, for example, grows aggressively and quickly establishes itself. People love it for that reason, but it also means bluegrass produces more thatch.
Those are best for areas that see a lot of foot traffic, like sports fields. Choosing or mixing in some perennial ryegrass or tall fescue will cut down on thatch production in your lawn.
Test your soil periodically for its nutrient levels and acidity. Find out how much lime you need to keep those levels where they’ll promote healthy lawn growth and microbial populations that break down thatch.
Good watering and mowing techniques, and proper fertilization can also hold down thatch. Make sure not to set your lawn mower too low, and don’t fertilize too heavily, which helps thatch build up rapidly.