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Dethatching

What is thatch?


Thatch is the layer of living and dead stems, roots, stolons, and rhizomes between the green blades of grass and the soil surface. A thin layer of thatch (less than 1/2 inch thick) can be beneficial to the lawn because it helps to limit weed germination, reduce water evaporation, and protect from frost damage. However, thick thatch layers can prevent water, air, and nutrients from penetrating the soil, causing reduced root growth and increased potential for drought stress. Thatch also favors fungal growth and can harbor insect pests. Some turfgrass species, such as tall fescue and perennial ryegrass, do not produce much thatch. Other turfgrass species, such as bermudagrass, bentgrass, and Kentucky bluegrass, have creeping growth habits and rapidly build thick thatch layers.

 

Dethatching methods


Using a thatching rake


A thatching rake, available at lawn and garden stores, can be used on small lawns. A thatching rake has thick blades that are designed to dig into the turf and loosen the thatch layer.


 Pull the rake across the lawn, bringing the thatch up to the soil surface.
 Remove and discard the debris.


Using a vertical mower


For large lawns, use a vertical mower to cut through the soil surface. Known as a verticutter or dethatcher, this mower has a series of revolving blades that cut through the thatch and bring it to the surface. The depth to where the vertical blades penetrate is adjustable and should be determined by thatch thickness and your turf species. These mowers can be rented at rental equipment centers. It may be more convenient to have a professional do the job for you.


 In general, grasses with a creeping growth habit tend to produce heavier thatch layers than bunch-type grasses so set the blades so that they cut about 1 inch into the soil and 1 inch apart.
 For bunch grasses, set the blade higher and further apart.
 Before dethatching, mow your turf a little lower than you normally would and lightly moisten the soil surface.
 Run the verticutter across the lawn in one direction.
 Once you have dethatched the entire lawn, make a second pass over the lawn at an angle perpendicular to the first pass.
 Remove the debris with a rake and dispose of it.
 Follow up by aerating, fertilizing, and watering as needed.
 Overseed as necessary.

 

When to dethatch


Timing


If your lawn has a bouncy feel to it when you walk on it, thatch is probably building up. As a general rule, plan to dethatch your lawn when the thickness of the thatch is more than 1/2 inch deep. To determine the thickness, remove a small square of your lawn to a depth of about 3 inches and measure the brown layer between the grass blades and the soil surface.


For both cool and warm-season grasses, the best time to dethatch is mid-to-late spring or early fall. During this time when the turf is actively growing, the grass will quickly recover from injury.


Frequency


The frequency of thatch removal depends upon how fast the thatch layer builds. Lawns that are overwatered, overfertilized, or growing on heavy clay soils may accumulate thatch quickly. Turfgrass species is also a factor. Grasses such as bermudagrass, bentgrass, and Kentucky bluegrass build a thick thatch layer over several months and may need to be dethatched yearly. Grasses such as tall fescue and perennial ryegrass do not produce much thatch and may not need to be dethatched more than every few years.


What to watch out for
Avoid dethatching when weeds are germinating to prevent them from invading your turf. If you are planning to apply preemergence herbicides, do so after dethatching. Otherwise, the herbicides may bind with the thatch and decrease their effectiveness.