Lawn Thatch

Thatching and De-thatching Lawns

  GRUB DAMAGE    A thick thatch layer provides good cover for grubs by intercepting grub controls.

GRUB DAMAGE
A thick thatch layer provides good cover for grubs by intercepting grub controls.

What's the origin of thatch problems in lawns?

The first seven years with a new home lawn has been called the "Honeymoon" period.  Most of the reason behind that nickname is the absence of a harmful thatch layer that is over one-half inch thick. 

Up to one-half inch of thatch depth is considered alright, with minimal thatch even being considered beneficial. However, when thatch exceeds one-half inch in depth, serious problems begin to occur. It really gets serious when thatch reaches one inch thick.


GREEN-UP AND GROW!
One of the main contributors to thatch development is ongoing heavy nitrogen fertilization. Nitrogen is the first number on a fertilizer label and the nutrient that pushes grass to green-up and grow.


ROOT STRUCTURE
Some varieties of grass, such as Kentucky bluegrass, tend to produce thatch due to the growth habit of their roots (rhizomes). Heavy clay soil can also contribute to more rooting on the lawn surface, instead of into the soil beneath. Aerating a lawn at least once annually helps to combat these poor rooting situations, as well as preventing thatch build-up.

   Core aeration combats thatch problems if done once or twice a year.

Core aeration combats thatch problems if done once or twice a year.

MULCH YOUR GRASS CLIPPINGS?
Mulching clippings will not contribute to thatch in normal situations, where there isn't already a thatch problem. In heavily thatched lawns it will be beneficial to bag and compost clippings, since clippings are less likely to reach the soil surface where microbes can break them down naturally.


How to prevent thatch problems

In order to prevent thatch problems there are several measures which can be practiced annually, preferably in the early fall (September in the midwest and northeastern United States)

  • PUNCH IT OUT
    Core aeration done once or twice annually, involves "plugging" the lawn with a "hollow-spoon" aerator. SEE VIDEO BELOW.
  • POWER RAKE
    De-thatching once every year or two, involves mechanically removing some of the dead debris from the lawn surface.
  • LIGHT LIMING
    While the soil pH of a lawn can be in the proper range and not require lime, a light application of lime will benefit thatch decay.
  • PROBLEM CASES
    In cases where thatch build-up has exceeded 1-inch, Bob recommends stripping the lawn down to the soil with a sod-cutter and starting from scratch with a new lawn.  At this extreme thatch thickness, it would take several years to reduce the thatch to an acceptable level using normal means, with costs in the long run being about the same. Seeding a completely new lawn also allows for the introduction of improved turfgrass varieties which weren't available 50 years ago.


Starting a new lawn from scratch...

   Sod-cutter set deep enough to get all the thatch without removing excess topsoil.

Sod-cutter set deep enough to get all the thatch without removing excess topsoil.

   Thatched lawn (top) Soil level (bottom)

Thatched lawn (top)
Soil level (bottom)

   Sod cutting in progress with old thatch pieces rolled-up.

Sod cutting in progress with old thatch pieces rolled-up.