Thatch is a tightly intermingled layer of living and dead stems, leaves, and roots which accumulates between the layer of actively growing grass and the soil underneath. Thatch is a normal component of an actively growing turfgrass, and as long as it is not too thick, it can increase the resilience of the turf to heavy traffic. Thatch develops more readily on high-maintenance lawns than on low-maintenance lawns.
A thin layer of thatch will insulate the lawn, protecting the roots from high heat, and will aid in water retention. But when the buildup becomes too thick, more than 1/2 inch, it becomes an unhealthy element for the lawn. The roots will grow in the thatch and not make it to the dirt below, which will limit the ability of the grass to take in enough water and limiting its resistance to drought. You should check for excessive thatch buildup every fall as the weather begins to cool and the rains stop. For small thatch buildups, rake the lawn with a gardening rake or thatching rake. Use a mechanical dethatcher when the thatch buildup is more than one inch. Dethatch during warm, but not hot weather, in the early spring or fall. Aerate the lawn every two or three years.
Dethatching your lawn improves its overall health. When you dethatch, you actually cut through the thatch with knife-like blades and then removing the debris. It is a combing like operation in which you comb out the debris. You can buy what’s called a thatching rake, which has knifelike blades rather than normal tines. You vigorously rake the lawn to remove the thatch, but it’s hard work and practical only for small lawns.
The more practical and effective method is to rent a gas-powered machine called a dethatcher, vertical mower, or power rake. Available at your local rental yard, a dethatcher cuts through the thatch with rotating blades or stiff wire tines. The machines can be fairly heavy and a bit difficult to maneuver, but they’re a lot easier to use than thatching rakes. For thick grasses like Bermuda grass and zoysia grass, use a vertical mower with steel blades. You can use the wire-tine type of dethatcher on Kentucky bluegrass or fescue lawns.
A dethatcher works best when the lawn is lightly moist — not too wet or too dry. Here’s how to do it:
- Mow the lawn a little lower than normal right before you dethatch.
- Make at least two passes over the lawn with the dethatcher to get all the thatch. Make the second pass at a 90-degree angle to the first.
- Rake up all the debris. If you haven’t used any pesticides on the lawn and it’s not a weedy grass like Bermuda grass, you can compost the debris or use it for mulch.
- Water and fertilize the lawn (according to your soil test results).Dethatching is pretty stressful on a lawn, and it can be on you, too. The lawn ends up looking pretty ratty, but if you dethatch at the right time, the lawn recovers quickly and fills in.
For a quicker fill-in, some people prefer to reseed the lawn right after dethatching. You simply spread the seed, rake the lawn so the seed gets down to the soil surface, cover with a light mulch, rake lightly again, and keep everything moist.
If you don’t want to reseed but worry that weed seedlings may take over before the grass recovers, apply a pre-emergent herbicide (it prevents weed seeds from germinating) after dethatching.