What’s the Difference Between a Core Aerator and a Dethatcher?

These two machines are efficient at helping to whip a struggling lawn back into shape, especially as the weather cools after a hot, punishing summer. One is a core aerator, and the other is a dethatcher – sometimes called a “power rake.”

What’s the difference between the two machines? And what situations call for which machine?

Core aerator

A core aerator is a machine with rotating rows of hollow, sturdy-metal tubes. The tubes remove two- to three-inch-long plugs (cores) of soil, then deposit them on top of the ground. 

This creates new air space that allows soil particles to move apart, helping to improve the compacted ground. Removing soil cores does a better job than spike aerating, which simply stabs holes in the soil without creating new space for expansion. Core aeration also aids root growth and improves the lawn’s ability to take in oxygen and water.

Core aerators are most effective when the soil is soft and damp, and they work best when done in two passes – once back-and-forth in the yard and again perpendicularly.

Most core-aeration machines are gas-powered, self-propelled, and walk-behind, working much like a lawn mower, only heavier and with rotating tubes instead of horizontally spinning blades.

Models also are available that can be pulled behind a tractor.

Read more on how and why to core-aerate a lawn

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Dethatching machine

A dethatcher or power rake is also typically gas-powered, self-propelled, and walk-behind, except the machine’s underside has vertically rotating blades or tines that tear a few inches deep into the soil. (Tractor-pulled dethatchers also are available.)

Instead of removing cores of soil, dethatchers are designed to remove and pull up thatch from the lawn. Thatch is a spongy layer of surface roots and decaying plant matter between the soil and the grass crowns, where new blades emerge. A thatch layer of less than a half-inch is normal and healthy. It cushions foot traffic, insulates grass roots, and is home to beneficial soil microbes and insects.

However, when factors such as over-fertilizing and frequent shallow watering cause thatch to build up more than a half-inch, lawns struggle. Symptoms include less drought tolerance, less oxygen reaching the roots, and increased lawn disease.

Warm-season grasses such as Bermuda grass, buffalo grass, and St. Augustine grass are particularly prone to excess thatch, although Kentucky bluegrass, bentgrass, and some fescues are cool-season species that are somewhat thatch-prone.

In small lawns, stiff thatching rakes – sometimes called “convex rakes” – can do the job by hand. But for deeper problems and bigger areas, renting a dethatching machine is more labor-effective.

Dethatching can be done anytime the lawn is actively growing, but early fall is one good time as grass growth picks up from cooling temperatures and more regular rain.

The torn-up grassy debris will end up on top of the lawn after dethatching, so a raking or mowing with a bagging attachment is needed to remove it.

As with core-aerating, two perpendicular passes are best.

Read more on how to prevent and control excess thatch on the lawn

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When to use which machine?

A core aerator makes the most sense when the main problem is compacted soil. It’s a way to gradually improve stunted growth without having to dig up the whole lawn, till the soil, and work in compost or similar organic amendments before replanting.

A dethatcher makes the most sense when the main problem is a too-thick layer of thatch. A core aerator can help break up thatch to some degree, too, but it doesn’t fix excess thatch as quickly and thoroughly as a dethatching machine.

Both machines can be used in cases where a lawn has both excess thatch and compacted soil.

And both machines are helpful for disturbing the soil before fall overseeding.

In the case of core aerators, some seeds fall into the core openings while others are covered as the cores on the lawn surface break down.

Before using either machine, know the location of any buried sprinkler lines or shallow cables since the tubes and blades will penetrate at least two inches.

Lawn-care companies usually offer both aeration and dethatching services, but both kinds of machines also are available from rental businesses for DIY lawn-owners.