How to Dethatch a Lawn

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Quick Tips

  • Causes of thatch are over watering, over fertilizing and mowing too high
  • Dethatch the lawn using a thatching rake or power dethatcher
  • After dethatching water, fertilize, and overseed

What is Thatch?

Thatch is a layer of living and dead stems, roots and crowns that develop between the green vegetation and the soil surface. Thatch acts as a barrier to water, nutrients and air reaching the soil and should be removed to ensure a healthy lawn. Learn how to reinvigorate a lawn by removing the thatch.

Milorganite. For Better Results. Naturally.

Step 1: Determine if the Lawn Needs Dethatching

If water runs off without penetrating the grass, then it may be time to dethatch the lawn. Thatch is a thin layer of organic debris that forms between the leaf blades and roots.  Examine your grass for an underlying layer of thatch. It will look like a matting of old, grayish-brown grass stems that have grown together. A thin layer of thatch (½ inch or less) provides insulation against temperature extremes and fluctuations in soil moisture.  However, if your lawn has more than one inch layer of thatch above the soil surface, the lawn needs to be dethatched.

Note: Primary causes of thatch are over watering, over fertilizing and mowing too high. To help prevent thatch from forming, use a mulching mower.

Step 2: Dethatch the Lawn

The best time to dethatch cool-season grass is in late summer or early fall when the grass is actively growing.  For warm-season grasses, dethatch in late spring.

In the spring and for small areas use a thatching rake, which is a sharp-tined rake that rips the thatch out of the lawn.  Leaf rakes or hard rakes can be used but may not work as well. Rake the grass, digging deep to penetrate the thatch and loosen it apart. In the spring removing thatch by raking is best to prevent damaging new growth.

In the fall and for large lawns, run a power dethatcher over the lawn in a pattern that covers the area only once. When using a power dethatcher, flag irrigation heads and other hidden objects in the lawn to prevent damage. When the task is finished, the lawn will look terrible, but don't panic. It's supposed to look that way.

Note: You can rent a power dethatcher from most garden centers. Enlist the help of a couple of friends and a truck when picking up the equipment as it can be heavy and awkward. Read the operator's manual carefully prior to use.

Step 3: Clean-up and Water

Rake up the debris with a leaf rake and place it in the compost pile. Water the lawn.

Next: Aerate, Overseed, Fertilize

After dethatching your lawn it is a great time to aerate your lawn.  After aerating, overseed and fertilize with Milorganite. It should take about 3-4 weeks for the lawn to recover and show signs of new growth.