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