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What is Thatch, how does it form and why is Thatch bad for my Lawn

Shallow Lawn Thatch Thatch is a layer of natural decaying and dead leaf litter and other plant materials that builds up on the top of the soil surface at the base of the grass plants. Over time, especially if it is allowed to dry out, it can become fibrous and matted like a dry old bathroom sponge.

The picture details shallow lawn thatch. How does Thatch form? Turf grasses predominately grow in a tufted habit with a few exceptions between turf grass species. Imagine a pile of letter 'V's slotted inside each other with one central upright.

As a new grass leaf grows, a new letter 'V' is formed inside the uppermost existing 'V' and the growth cycle continues over time. When you have around five 'V's stacked inside each other, so approx 10 leaves, five each side, the older leaves on the bottom 'V' will die back and drop away. As more 'V's are added in the centre of the stack, the old 'V's at the bottom of the stack disappear as new ones arrive as only 5 are allowed in the stack. A typical established turf grass will have around 8 - 10 leaf stages when fully developed.

Some are newly generated grass blades and some are older leaves that make up each grass plant. The new grass blades grow from within the centre of the plant (intravaginal) with the older grass blades on the outer edges.

As the grass grows throughout the season, the older leaves naturally die back and fall away from the main grass plant and these find their way onto the surface of the lawn at the crown (base) of the plant.

Deep Lawn Thatch The old leaves will slowly rot and with other old decaying leaves, will start to build a small layer of what becomes known as 'thatch'. The action of lawn mowing, especially without the grass box will add more old vegetation to the surface of the lawn, adding to the thatch potential.  The picture shows a deep layer of lawn thatch.

Even mowing with a grass box will add some grass clippings to the lawns surface as some will miss the grass box all together. Leaf litter and other debris can add to thatch build up as can poor microbial activity in the soil which naturally reduce the thatch potential.

All grass clippings should be removed from the lawn after each mowing session. This picture details a severe case of deep lawn thatch. We scarify a lawn to remove the dead turf grass leaf litter material before it gets too excessive around the crown/base of the turf grasses in the lawn.

It is possible to bury an existing thatch layer with repeated top dressing, thus ending up with a fibrous layer of layer thatch deep within the turf grasses root zone. This will be a real problem to get rid of and requires removal by hollow tining.

Thatch is encouraged by:

  1. Excessive vegetative growth 

  2. Incorrect use of high Nitrogen fertiliser 
  3. Over watering 
  4. Low pH
  5. Low Oxygen levels in the soil 
  6. Irregular cutting heights 
  7. Uneven cutting 
  8. Not using a grass box

Thatch is undesirable in your lawn because:

  1. It prevents soil obtaining Oxygen, moisture and nutrients 

  2. Excessive water retention making a soft and wet spongy surface - thatch can be wrung out like a sponge 

  3. It is hydrophobic and cannot be easily re wetted once it dries out 
  4. Turf is more susceptible to pests and disease attack 
  5. Turf is more susceptible to drought.

 How to prevent Thatch:

  1. Sensible use of water and fertiliser 

  2. Regular mowing and alternating direction of cut to stop ‘wash boarding’ - this is where the grass may look short but if you back brush it, you will discover that the length of grass laying all the same way could be 150mm long. 
  3. Use of combs and brushes and grass boxes on mowers 
  4. Rake lawn with wire rake or Scarifier 
  5. Adopt a regular mechanical scarification program. 
  6. Aerate at regular intervals and do not apply too much top dressing at one time, otherwise the grasses are easily smothered and die out.

To cure lawn Thatch:

  1. Adopt a regular scarification and aeration program 

  2. Use a Wetting Agents to thoroughly wet the crusty lawn surface 
  3. Adopt a careful annual fertiliser programme 
  4. Aerate using a solid tine or hollow tine to remove a core from the lawns surface if thatch layer is deep. 5. Remember to remove the hollow tine cores from the surface of the lawn otherwise you will simply be adding to the thatch problem!! 
  5. It is now possible to apply a biological thatch control agent that introduces active soil microbes into the thatch layer. The microbes feed on the thatch and fibre that rapidly degrades thatch. Use this in conjunction with scarification and the thatch will reduce, reducing the probability of localised dry areas, turf grass stress, weeds and diseases. 
  6. If the surface of the lawn becomes dry and crusty over time and grass will not grow in these dry affected areas, you will need to use a Wetting Agent to alleviate what will become a Dry Patch that you will not become wet again via natural rainfall or artificial irrigation.

Thatch can be prevented and cured by regular Scarification and   Aeration

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