A spongy lawn that dries out fast, scalps easily and never seems to respond to fertilizer may have a thatch problem. Thatch builds up in a lot of Lowcountry lawns, especially zoysia and hybrid bermuda. Dethatching a lawn in Charleston can fix it, but it is also one of the easiest ways to badly damage a lawn if it is done at the wrong time or with the wrong settings. St. Augustine and centipede in particular do not tolerate aggressive power raking. Here is what thatch is, how to tell if you have too much, and how to remove it safely.
What thatch is and why it builds up
Thatch is the layer of living and dead stems, runners and roots that sits between the green blades and the soil. It is not made of grass clippings. Clippings break down quickly and are good for the lawn. Thatch forms from the tougher parts of the plant that decompose slowly.
A thin layer is fine. It cushions the lawn and helps it handle traffic. The problems start when it gets thick. Clemson Extension notes that thatch more than about half an inch thick makes watering difficult and can block water, nutrients and pest control products from reaching the soil. Roots start growing up into the thatch instead of down into the soil, which leaves the lawn shallow rooted and quick to wilt. Thick thatch can also harbor insects and disease.
Common causes of thatch:
- Vigorous grasses. Hybrid bermuda grows fast and builds thatch readily.
- Tough grasses. Zoysia has fibrous stems that break down slowly.
- Too much nitrogen. Heavy fertilizing pushes more growth than the soil can break down.
- Mowing too high or too seldom, leaving tall stems to fall over and pile up.
- Compacted or heavily treated soil with fewer earthworms and microbes to break down organic matter.
How to check your thatch
Cut a small wedge of turf a few inches deep with a trowel or knife. Look at the side of the plug. You will see green blades on top, a brown spongy layer in the middle and soil below. Measure that spongy middle layer.
| Grass | When thatch becomes a concern, per Clemson calendars |
|---|---|
| Centipede | More than about a quarter inch |
| St. Augustine | More than about half an inch |
| Bermuda | More than about half an inch |
| Zoysia | Heavy buildup, generally around an inch or more on the Clemson zoysia calendar |
If your layer is thinner than that, you do not need to dethatch. Core aeration and good habits are enough.
Dethatching a lawn in Charleston: when to do it
Timing is critical. Dethatching tears out a lot of plant material, so the grass needs to be actively growing to recover. Clemson recommends dethatching warm season grasses in spring after full green up or in early summer during rapid growth.
In the Lowcountry, that usually means late April through June, after the last frost threat. Avoid:
- Early spring, when the grass is still partly dormant and cannot recover
- Late summer and fall, when growth slows before dormancy
- Drought or extreme heat, when the lawn is already stressed
Dethatching and core aeration share the same timing window, and they are often done together. Like aeration, dethatching disturbs the preemergent barrier, so plan it around your preemergent schedule.
How to dethatch each grass type
Dethatching is done with a vertical mower, also called a power rake or verticutter. It has vertical blades that slice into the thatch and lift it out. The blade spacing and depth should change with the grass.
Zoysia and bermuda
These grasses spread by both above ground and below ground runners, so they recover better than St. Augustine or centipede. Clemson's general thatch guidance lists blades 1 to 2 inches apart for bermuda, cutting about half an inch into the soil. For zoysia, Clemson's maintenance calendar calls for 2 or 3 inch spacing at about a quarter inch deep and warns against power rakes with 1 inch spacing. Bermuda is often lowered before dethatching to make the job easier.
St. Augustine and centipede
These are the grasses where people get into trouble. They spread only by above ground runners, called stolons. If those runners get torn out, there is nothing underground to regrow from.
Clemson's specific guidance:
- Use blades spaced 2 to 3 inches apart, set shallow, about a quarter inch deep.
- Go over the lawn in one direction only. Multiple passes can injure or kill St. Augustine and centipede.
- Never use a power rake with close, 1 inch blade spacing on these grasses.
For many St. Augustine lawns, a light verticutting combined with core aeration and better fertilizer habits is safer than a hard dethatch.
Aftercare
Right after dethatching, the lawn will look rough. That is normal. To help it bounce back:
- Rake up and remove the debris. A lot of material comes up, and leaving it defeats the purpose.
- Water thoroughly.
- Feed lightly about a week later if a soil test supports it, and water it in. Keep feedings light on centipede, which does poorly with heavy nitrogen.
- Hold off on herbicides until the lawn has recovered.
With active growth, most lawns fill back in within a few weeks.
Preventing thatch from coming back
- Mow at the right height and frequency so you remove no more than a third of the blade at a time
- Fertilize based on a soil test instead of on a fixed heavy schedule
- Water deeply and less often
- Aerate compacted lawns during the growing season
- Leave clippings on the lawn, which does not add to thatch
Right Stuff Lawn Care handles dethatching and power raking with settings matched to each grass type, and we often recommend aeration alone when the thatch layer does not justify a full dethatch. Our mowing height guide covers the habit that prevents most thatch in the first place.
Frequently asked questions
Should I dethatch my St. Augustine lawn?
Only if the thatch is more than about half an inch thick, and only with care. Use wide blade spacing, a shallow setting and a single pass in one direction. For many St. Augustine lawns, core aeration is a safer first step.
What month should I dethatch in Charleston?
Late April through June is the usual window, after the lawn has fully greened up and while it is growing quickly. Avoid early spring, late summer and fall, when the grass cannot recover as well.
Do grass clippings cause thatch?
No. Clippings are mostly water and break down quickly. Thatch comes from tougher stems, runners and roots. Leaving clippings on the lawn returns nutrients to the soil.
Is dethatching the same as aeration?
No. Dethatching slices and removes the spongy layer of stems above the soil. Core aeration pulls plugs of soil to relieve compaction. They are often done together because they share the same timing.