It’s almost springtime and you want to get your lawn off to its best start. But what are dethatching and aeration? Are they the same thing? Are they even necessary? While thatch and soil compaction both stunt grass growth and cause bare patches, they need different fixes.
The difference is dethatching removes the too-thick layer of dead grass, stems, and roots that prevent water from reaching the soil and sun from reaching the grass blades. Aeration reduces soil compaction by adding holes in the soil for oxygen and moisture to reach roots and lower layers of soil.
Dethatching vs. Aerating Your Lawn
Lawn Dethatching
Before we get to dethatching, we need to know what thatch is. Thatch is the layer of living and dead grass shoots, stems, and roots that build up between the soil and the grass blades. (Thatch is NOT dead leaves or debris.)
Some thatch is beneficial to your lawn, as it shades the soil so your lawn needs less water and the thatch breaks down into nutrients to feed your grass.
However, when thatch becomes too thick (more than ½”), it can suffocate your grass, creating an anaerobic layer that prevents water, oxygen and amendments from reaching the soil and creates the ideal habitat for fungal diseases insect pests like sod webworms and billbugs.
Excessive thatch is generally caused by too much synthetic nitrogen or feeding lawns synthetic fertilisers when grass is heat-stressed or dormant. The excess nitrogen causes the grass to grow too quickly, which accelerates thatch buildup.
Synthetic nitrogen also has a nasty habit of killing off the beneficial microbes and worms found in your soil that would have otherwise broken the thatch down into nutrients that benefit your lawn. Switching to compost for a fertilizer will help reduce thatch problems over the long-term.
Another cause of excessive thatch is growing aggressive grass species like Kentucky bluegrass, creeping red fescue, and creeping bentgrass, or stoloniferous grass that spreads through above ground stems. Seeding with perennial grasses like perennial ryegrass and tall fescue will reduce thatch problems overall. These species also are hardier and lower maintenance.
Leaving grass cuttings on the lawn DOES NOT create thatch. Fresh grass clippings break down too fast. So unless your lawn has a thick thatch layer (thus preventing the grass clippings from reaching the soil), leave your grass clippings on your lawn to recycle those nutrients back into the soil.
Dethatching is the process of removing excess thatch and to prepare for fertilizing, overseeding, and restarting a lawn. Dethatching is done once or twice a year when your lawn is growing most vigorously. You can use a bamboo rake (which grips thatch better than plastic) or rent a power rake/dethatcher, a machine that’s kind of like a mower but removes thatch.
Thinking about dethatching your lawn? Our [pros and cons list for dethatching your lawn] will help you avoid making a costly mistake.
Lawn Aeration
Aeration is the process of adding small holes to your lawn to allow more oxygen and water to get to the roots. Aeration is used when the soil is compacted, which means that roots have less room to grow, water can’t easily soak in, and the roots don’t get any oxygen.
Your soil is compacted if:
- Water runs over the soil without sinking in.
- Puddles form on your lawn and take hours or days to disappear.
- Grass grows patchy with bald spots.
- Either weeds that thrive in compacted soil take over or the soil is so hard that not even weeds will grow in the bare spots.
- The soil is difficult to pierce the soil with a shovel or trowel.
- Your soil is heavy clay.
Soil compaction is caused by heavy clay soil, heavy foot traffic, driving heavy mowers or vehicles over the lawn while wet, or from a lack of organic matter in the soil. Compost will help aerate your lawn over a few years.
There are 2 types of aerators:
- Spiked devices, which drive a spike into the lawn to open up a hole, but also compacts the soil around the hole. Avoid using when possible.
- Core aerators, which cut up plugs of grass and soil the size of a finger and deposits them onto the soil. These devices don’t compact the soil. You don’t even need to pick up the plugs as they’ll quickly break down. The downside is that they’re heavy and more difficult to use than a mower or power rake, so you need to be in superb shape to use one. For the rest of us, it’s better to hire a contractor.
Aeration is best done in the mid-summer (warm-season grasses) or autumn (cool-season grasses) as weeds will take advantage of the open soil.
Is your lawn in need of aeration? Check out our easy 5 step guide to aerate your lawn.
| Dethatching | Core Aerating | |
| What It Does | Removes the buildup of living and dead grass material that builds up between the soil and the grass blades. | Digs up finger-sized plugs of soil to relieve soil compaction and give grassroots room to grow and oxygen to breathe while allowing water to reach the lower soil layers. |
| Issue Addressed | Excess thatch (above ½”) or removing thatch before overseeding | Soil compaction. |
| When to Use | ● When thatch grows thicker than ½”, preventing air and water from circulating to the soil and roots.
● To prepare the lawn for overseeding by removing the obstacles between seed and soil. |
● Puddles form and hang around after watering/rain
● It’s difficult to pierce the soil with a shovel. ● The soil is heavy clay. ● Your grass is patchy, and possibly even weeds won’t grow. ● To prepare the lawn for overseeding. |
| Best Time to Use | ● When the lawn is growing most vigorously and the soil is moist.
● For cool-season grasses, that’s mid to late spring or early to mid-fall. ● For warm-season grasses, that’s midsummer. |
● When the soil is not too dry or too moist.
● When overseeding if there’s soil compaction. ● When grass is growing most vigorously. |
| When Not to Use | ● When the grass is dormant or slow-growing as the process will damage the grass.
● When the thatch is less than ½” thick |
● When the soil is loose and the grass can easily grow roots.
● Unless necessary, avoid doing it in spring as it opens up space for weed seeds to germinate. |
| Long-Term Solutions | ● Switch from synthetic fertilisers to compost
● Seed grasses that are less thatch-prone, like perennial ryegrass and tall fescue
|
● Use compost topdressing twice-a-year to aerate the soil over time
● Avoid compacting the soil with heavy foot traffic and machinery when the soil is wet |
Dethatching VS Aerating FAQs
Is Dethatching or Aeration Better for Overseeding?
Both dethatching and aeration have a part to play in overseeding, and which you use depends on your lawn’s condition.
If your soil is compacted, then you will need to aerate anyway or your grass seeds won’t be able to grow very strong. If your soil is not compacted, then you don’t need to aerate.
If you have too much thatch, then the seeds won’t reach the soil where they germinate. For this reason, you may want to dethatch even a shorter layer of thatch.
Should I Dethatch or Aerate First?
Dethatch first, aerate second. Dethatching will remove all the excess buildup before you run a core aerator over an area.
Can You Dethatch and Aerate at the Same Time?
If the thatch buildup isn’t too thick, then you can just use core aeration, which will remove some thatch buildup at the same time as it aerates the soil. Other than that, the tools to dethatch and to core aerate are different, so you can’t do them at the same time. You can do both on the same day, dethatching first then core aerating directly after.
How Much Does It Cost to Dethatch a Lawn?
The cost for dethatching depends on what you need. You can easily dethatch yourself, either with a rake or by renting a power rake/dethatcher. If you can use a lawn mower, you can use a power rake.
Thatching rake: $25 – $50
Power rake/dethatcher rake rental: $70 – $100 (half or full day)
Contractor: $100 – $500 (depends on how big your yard is and additional services)
How Much Does It Cost to Aerate a Lawn?
While dethatching is something you can do yourself, a core aerator is a much more unwieldy beast. Unless you’re in terrific shape and really want to DIY it, your best option is to hire a contractor. They may give you a package deal with dethatching and overseeding too.
Aerator rental: $70 – $100
Hiring a contractor: $75 – $200 (depends on how big your yard is and additional services)
Final Thoughts
In lawn care, sometimes less is more. You don’t always need to aerate or dethatch. Knowing when and when not to dethatch or aerate will help you avoid making costly mistakes.
Jamie is the founder of The Backyard Pros. When he was 15 years old he started working at a garden centre helping people buy plants, gardening products, and lawn care products. He has real estate experience and he is a home owner. Jamie loves backyard projects, refinishing furniture, and enjoys sharing his knowledge online.