How to Dethatch St. Augustine Grass [7 Easy Steps]

Use a vertical mower to dethatch St. Augustine grass in spring. This process will remove excessive thatch from your lawn, allowing your grass to more easily take in nutrients from fertilizer and water. Too much thatch will strangle your St. Augustine grass and invite diseases that can wipe out whole portions of your lawn.

After dethatching, use a core aerator to loosen the soil in your yard. Follow this up by applying fertilizer to help your grass recover from the stress of dethatching and aeration. Complete your spring lawn care with a St. Augustine watering schedule and regular mowing.

How to dethatch St. Augustine grass

7 Steps to Dethatch Your St. Augustine Yard

Dethatch at the Right Time

Dethatch St. Augustine in spring, when the grass has exited winter dormancy, greened up, and grown high enough to be mowed.

  • Dethatch in spring, between March and May.
  • After spring green-up, when your lawn has been mowed at least once.
  • Do not dethatch in fall or winter. This can seriously damage St. Augustine.

Dethatching places stress on the grass plants in your lawn. By dethatching in spring, your St. Augustine has the entire growing season to recover ground and fill in your lawn. A St. Augustine lawn dethatched in fall or winter will struggle to recover and may die in places.

Check to See if Your St. Augustine Needs Dethatching

How can you tell if your lawn needs dethatching? Use this simple test to find out:

  • Use a small hand shovel to dig up a section of grass, 3 inches square and 3 inches (7.5 cm) deep.
  • Use a ruler or tape measure to find the thickness of the thatch layer. This is the mat of brown stems and dead material between the green grass and the soil.
  • If the thatch layer is 1/2 inch (1.25 cm) or less thick, you don’t need to dethatch.
  • If the thatch layer is greater than 1/2 inch thick, your lawn needs dethatching

Because St. Augustine spreads by aboveground stolons (runners) only, thatch is extremely harmful to it. The stolons can’t send roots down through the thatch and form new grass plants. This prevents your St. Augustine from spreading and filling in your yard.

Mow Before Dethatching

Prior to dethatching, mow St. Augustine to a height of 2 inches. This allows the dethatcher to reach past the living grass and pull up the thick mat of thatch.

  • Before dethatching, cut St. Augustine to 2 inches.
  • Mowing low will allow dethatching tools to reach past living grass and remove thatch.

Although St. Augustine typically thrives at a blade height of 3–4 inches, mowing your entire lawn low before dethatching is essential to get the most out of your work.

Choose the Right Dethatching Tool

The best tool to dethatch St. Augustine is a vertical mower. This tool can be rented at most local hardware stores. It does the best job at removing heavy thatch from St. Augustine without damaging the grass. Do not use a power rake to dethatch St. Augustine, as these can damage St. Augustine stolons and make it difficult for grass to recover.

  • Use a vertical mower to dethatch St. Augustine.
  • Avoid power rakes (sometimes called dethatchers), as these can cause serious damage to St. Augustine.
  • In small yards under 1,500 square feet, St. Augustine can be dethatched with a simple thatch rake.

The least damaging way to dethatch St. Augustine is by using a dethatching rake. However, this is a manual process that is more time and labor-intensive than vertical mowing. It is best used for small sections of the yard.

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Dethatch with a Vertical Mower

Set the blades of your vertical mower 3 inches (7.5 cm) apart prior to dethatching. This is the proper width to dethatch St. Augustine without damaging it. Then, dethatch your yard, making sure to dethatch each area only once.

  • Set vertical mower blades 3 inches apart.
  • Make a single pass with the vertical mower over your lawn, as you would with a standard lawnmower.
  • Rake and bag thatch to dispose of it or add to compost.

After dethatching, remove the dead, brown material from your lawn. Thatch is made up of stems and stolons that resist decomposition. Thatch left on your yard won’t break down into organic matter easily.

Aerate Your Lawn

The best time to aerate your St. Augustine lawn is just after dethatching. With less thatch to impede your aerator, aeration will be more effective. Not only that, but aerated soil absorbs water, air, and nutrients more easily, speeding your St. Augustine’s recovery from dethatching.

  • Use a core aerator after dethatching to loosen soil and speed lawn recovery.
  • Aeration is most effective when thatch is thin. Plan for spring dethatching and aeration.

Dethatching, followed by aeration sets your lawn up for a spring and summer growth boom. Your lawn may look a little thin just after dethatching, but aeration puts your grass on the road to recovery.

Fertilize Newly Thatched St. Augustine

A slow-release nitrogen fertilizer applied to a newly thatched lawn will boost growth and recovery at the same time it prevents weed invasion. If your St. Augustine hasn’t benefited much from fertilizer applications in the past, this time may be a different story. By eliminating thatch, you allow more fertilizer to reach the soil and feed grass roots.

  • A heavy thatch layer prevents fertilizer from reaching the soil.
  • Newly thatched and aerated soil absorbs fertilizer at high rates.
  • To boost spring and summer grass growth, use this fertilizer on your dethatched St. Augustine.
  • Fertilizer application after dethatching promotes thick grass growth and helps St. Augustine resist weeds.

Within a few weeks of fertilizer application, your St. Augustine will have bounced back. It will be much greener and more vibrant than before dethatching. Excessive thatch can lead to a brown, patchy appearance, but dethatching and fertilization will turn your lawn into a green paradise.

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What is the Danger of Too Much Thatch in St. Augustine?

When St. Augustine thatch grows thicker than 1/2 inch, it begins to act like a sponge, stealing moisture from the soil and becoming a spongy mass that harbors mold and disease, such as gray leaf spot. Not only that, but any fertilizer you spread will be trapped in the thatch layer. It won’t reach the soil level where it can feed your lawn.

  • Robs water from living grass, leading to drought-stricken St. Augustine.
  • Prevents nutrients in fertilizer from reaching the soil to feed living grass.
  • Promotes diseases, including grass fungus and pest insects.
  • Thick thatch will cause St. Augustine to struggle and die.

An overly thick layer of thatch will kill your St. Augustine grass in patches. This is because thatch prevents St. Augustine from spreading to repair itself at the same time it robs up to an inch of water from the topsoil. This deadly combination leads to a lawn that grows thin and sickly over time.

How Often Should You Dethatch St Augustine?

Check the thickness of the thatch layer in your St. Augustine turf each spring. If the thatch is more than 1/2 inch thick, perform the steps above to reduce thatch and boost lawn health. If the thatch is 1/2 inch or less thick, you can wait until next spring before testing again.

  • Test thatch thickness each spring (March/April).
  • Some St. Augustine lawns require annual dethatching, while others may only need thatching every 2 years.

How often your lawn needs to be dethatched depends on several factors including irrigation and fertilization schedules. How quickly thatch builds up in your lawn depends on the local climate and your lawn care practices.

How Do You Remove Thatch From St Augustine Grass

To get rid of excessive thatch buildup in St. Augustine grass, follow these steps:

  • Plan to dethatch in spring, between March and May.
  • Test thatch thickness. If it’s more than 1/2 inch, your St. Augustine needs dethatching.
  • Mow your lawn to 2 inches in height prior to dethatching.
  • Dethatch your lawn with a vertical mower with blades set 3 inches apart.
  • Remove loosened thatch debris from your lawn.
  • Use a core aerator to loosen the soil after dethatching.
  • Apply a slow-release nitrogen fertilizer to help your lawn recover and thrive.

This dethatching plan is excellent for St. Augustine turf grass and will help promote healthy grass that resists drought, weeds, and disease. A vibrant lawn created by proper dethatching will make ongoing care and maintenance easy and hassle-free.

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