Can You Dethatch Tall Fescue?

When to Dethatch Tall Fescue

• Like other species of turfgrass, plan to dethach a tall fescue lawn when a thatch layer more than 1/2 inch thick develops. Use a small spade to dig up a wedge of soil and turf and measure the thickness of the layer of brown debris atop the soil surface. Often, a lawn is in need of dethatching when it has a bouncy feel underfoot. Lawns with thick thatch are also prone to scalping, can suffer from drought stress even with adequate rainfall or irrigation and are particularly susceptible to certain fungal diseases and pest problems. Time the tall fescue dethatching for early fall or mid-to-late spring when you anticipate at least 45 days remain in the growing season for the grass.

Thatch Removal

• Prior to dethatching, mow the lawn slightly lower than normal and lightly water the soil surface. For small areas where the thatch layer is not very stubborn, a dethatching rake is often appropriate for the task. This tool, which resembles a sturdy garden rake, is pulled across the soil surface in the lawn area to break up the thatch. For larger areas, a machine known as a vertical mower, or verticutter, is often more effective. This machine, available for rent at many garden or equipment centers, features a series of rotating blades designed to cut through the thatch layer. For vigorous, creeping grass species the blades are set relatively close to each other and low; for tall fescue the blades should only barely contact the soil surface and can be spaced about 2 to 3 inches apart. Once that thatch layer is broken up, the debris is raked up and removed.

Care Following Dethatching

• Dethatching is an injurious process and can have a negative impact on the tall fescue, causing or revealing bare spots. Because tall fescue is a bunch-type grass, it will not quickly recover to fill in bare spots and may require re-seeding. If the soil in the site is compacted or the site is weedy or lacks fertility, follow the dethatching with aeration and preemergent herbicide and fertilizer applications. Do not apply any preemergent herbicide if you plan to overseed the site. To overseed a tall fescue lawn that has bare a spots, use 3 to 8 pounds of seed per 1,000 square feet of lawn area, depending on the extent of the bare spots. Water the site regularly to maintain even moisture around the seeds and encourage germination and seedling growth.

Lawn Care to Minimize Thatch

• Proper lawn care practices will help to slow the accumulation of thatch or can even slightly reduce a thatch layer's thickness. Mow the tall fescue at a height of 2 to 3 inches and cut the grass frequently enough that you never have to remove more than a third of the grass blade with a single mowing session. Do not over-fertilize the lawn; use slow-release nitrogen rather than quick-release or water-soluble fertilizers. Water the grass deeply and infrequently instead of using shallow, infrequent irrigation. Occasionally topdress the lawn by evenly broadcasting 1/8 to 1/4 inch of topsoil or compost over the lawn area to help break down the thatch layer by introducing additional microbes to the debris.