About De-Thatching a Lawn

A healthy thatch layer on your lawn helps hold in moisture and prevent drought or heat stress. Excessive thatch build-up, however, can lead to a variety of problems with your lawn's health and appearance. When done properly, de-thatching can help revitalize your grass and reduce lawn maintenance and repair costs.

Identification

Thatch is a layer of cut grass, plant stems, roots, leaves and other debris that collects on the soil, below live blades of grass that form the surface of the lawn. Dig down with a shovel blade and pull out a chunk of turf grass and soil to help you identify the three separate layers: grass, thatch, and root and soil system. The thatch will be the brown layer of dead grasses and roots at the center, and in healthy lawns is 1/2-inch thick or less.

Function

De-thatching is used when the thatch layer is over 1/2-inch deep and the lawn shows signs of distress, like browning and thinning patches of grass. The de-thatching process removes the barrier to the soil, tearing it up to be raked away, while preserving the actively growing grass. Homeowners should remove the thatch layer when necessary to allow water and nutrients back in, and improve the lawn's health and appearance.

Types

A hand rake made with sharp blades that tear at the loose underlayer can be used to de-thatch the lawn. This method is labor-intensive and best used with small lawns or patches of grass. For larger jobs, use a mechanical de-thatcher. Bachman's Landscaping recommends a vertical mower. This machine operates like a lawn mower, with several blades to quickly tear at the thatch.
In less severe cases, aeration can de-thatch the lawn by pulling up microorganisms deep in the soil. These microorganisms will naturally digest the thatch and convert it to nutrients for the lawn.

Time Frame

De-thatching should be done in late spring or early fall. De-thatching when grass is actively growing assures that any existing bare spots, or grass roots torn out by the process, will fill in quickly with new growth. De-thatch the lawn every two to three years, or every year for lawns prone to distress.

Considerations

Be aware that de-thatching too early in spring can tear up too much of the newly returning grass. Cut the grass shorter than usual before the de-thatching process to make removal easier.
When using a mechanical de-thatcher, be cautious of setting the blades too low. Start with the higher settings, then gauge the results and adjust accordingly. Vertical mowers and other de-thatching devices can be difficult and strenuous to operate, so consider hiring a professional to do the job.
Apply weed herbicides after the de-thatching, when they'll be more easily absorbed and effective.

Benefits

De-thatching increases the amount of water and nutrients penetrating the soil. It allows grass to develop a deeper root system, which leads to thicker, heartier lawns. Regular de-thatching removes thick underlayers that can hold moisture and lead to fungal and pest infestations.
Aesthetically, de-thatching gets rid of the unattractive brown layer of dead and decaying lawn debris, leaving only green grass behind and fostering new growth.

Prevention/Solution

The University of California Agriculture Department recommends three processes to prevent thatch build-up. Avoid over-fertilizing, particularly excessive amounts of nitrogen. Rake up grass clippings if there's been excessive growth between mowing. Avoid frequent, shallow watering that causes short root systems as well as excessive surface moisture that can lead to weed growth and disease.
When re-seeding a section of lawn, consider perennial ryegrass and tall fescue as they are less prone to thatch problems. Be wary of creeping growth turf grass like bermuda grass and Kentucky bluegrass, which are more likely to develop an overabundance of thatch.