First aid for your lawn: thatch

June 19, 2015

Thatch is a fibrous mat of dead stalks and roots that settles between the lawn's green leaves and the soil. It's a sign of poor health, so here's how to remedy it.

First aid for your lawn: thatch


  • If your grass feels soft and spongy when you walk on it, your lawn may have a thatch buildup.
  • When your lawn's fibrous mat becomes greater than 2.5 centimetres (one inch) thick, it can cause your lawn to suffer from heat and drought.
  • Affected lawns will rapidly wilt and turn blue-green, indicating they're hot and dry.


  • Cutting off too much at each mowing (letting the grass get too long) and cutting too low. Both will produce more dead grass tissue than microbes and earthworms can recycle.
  • Thatch can develop in any soil but is most often associated with high clay content.
  • Other causes are overfertilization and frequent, light watering, which encourage a shallow root system.


  • Slice open a section of your lawn.
  • If your grass shows 2.5 centimetres (one inch) or more of thatch, it's time to rent an aerator.
  • An aerator is a heavy machine that opens the soil by pulling up finger-sized soil cores. The lawn will absorb more oxygen and water, which will encourage healthy microbe growth and give worms wiggle room.
  • Aerate in the spring or fall when the grass is growing but the weather is not too hot to stress the plants.
  • If the machine isn't pulling plugs, your lawn may be too dry.
  • To avoid this problem, water thoroughly the day before you aerate.
  • You can also rake in topsoil to increase the healthy microorganisms that aid thatch's natural decomposition. Topsoil is available at any garden centre.

Recovery time

You can expect the thatch layer to decrease by about half a centimetre (a quarter inch) per year, about the same rate at which it forms.

How to prevent thatch

1. Mow often and cut no more than one-third of the grass height.

2. Water your lawn less often but for longer periods to prevent shallow root systems.

3. Reduce the amount of fertilizer you spread at any one time.

4. Reduce the use of pesticides. This will help keep the worm and microorganism populations healthy.

5. Aerate at least once every year if your lawn is prone to thatch.CAUTION: Be sure to call your local utility provider to mark your underground utility lines before you aerate.

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