What is thatch and how do I know if I have it?

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What is thatch and how do I know if I have it?
What is thatch?

Thatch is a layer of organic matter that gathers between the grass blades and the surface of the soil. It is largely made up of dead grass but also a build-up of fallen leaves and any other bits of organic debris that find their way onto your lawn.

The largest build-up comes from the grass itself; as it naturally dies, it falls to the surface of the soil and gathers, whilst it is replaced by new grass shoots. These new shoots come from the parent plant and either grow stems above the surface (stolons) or below (rhizomes), during which time this new growth knits the fallen grass together to become denser and thicker. Dying grass and moss contain lignin which is slow to decompose and over time this builds up and becomes thatch.


Is thatch good for my lawn?

As long as it is managed correctly, some thatch is considered a part of a healthy lawn but too much is where the real problems can begin.


How to spot thatch in my lawn?

The best way to examine your lawn for thatch is to take a soil core sample. This will allow you to see a cross section of your lawn and therefore enable you to see the depth and density of the thatch.

In severe cases, when walking on the lawn the thatch will feel spongy under foot, this is not uncommon on untreated lawns.

During your lawn assessment our So Green lawn care manager will take a soil core sample so they can see how much thatch you have and will discuss treatment options with you if they think your thatch requires attention.  


What is the right amount of thatch?

Around 0.5cm – 0.75cm of thatch is considered to be a healthy amount. A thatch layer over 1cm – 1.5cm in thickness means you need to act as this will be inhibiting the healthy growth of your lawn.

Advantages of managed thatch
  • Thatch can aid water absorption, as the layer acts as a sponge and will slowly release water into the soil.
  • It insulates the grass and protects it from extreme heat and cold temperatures, whilst reducing the drying effect from the wind during dry periods.
  • It protects the top of the grass plant (crown) from impact and compression.
  • Thatch deters moss and weeds from growing by filling any gaps that they might flourish in.
  • It can promote healthy soil as some thatch gets broken down and decomposed by soil bacteria and the nutrients absorbed and reused.
Disadvantages of too much thatch:
  • A heavy thatch layer can act as a barrier stopping moisture, vital nutrients and fertiliser penetrating down into the grass roots.
  • It can stop air reaching the surface of the soil which is vital for a healthy soil ecosystem.
  • Thick thatch can create the ideal conditions for unfriendly bacteria and fungi to breed and develop which can lead to lawn diseases.
  • It prevents new grass from growing as it inhibits sunlight from reaching the soil surface.
  • New grass may start to take root in the thatch which is holding the water, as moisture will no longer be reaching the soil.


Which treatments tackle thatch?

A healthy lawn environment and a regular and efficient lawn care programme is the key to dealing with thatch.

Within your lawn care programme there are a couple of treatments that are very effective against thatch build up:

  1. Scarification is the most effective treatment against thatch; the combing action pulls out any organic matter that has built up – you’d be amazed at quite how much thatch we pull out!
  2. Hollow-Tine Aeration; we recommend this as a yearly treatment to assist in the prevention of thatch build up. It allows air back into the soil, improving the health of the soil ecosystem and therefore aids in the breaking down and reduction of the thatch layer.

As always we recommend keeping your lawn clear from debris and clearing all grass clipping when mowing the lawn.