Thatch refers to the layer of organic matter that accumulates on the surface of a lawn.
The thatch layer consists of dead grass leaves, roots and other parts of the grass plants such as stolons and rhizomes. This layer forms naturally as the grass plants grow.
A healthy lawn often recycles this material back down into the soil, maintaining a thin thatch layer. When a lawn is overfed, has long clippings left on the surface or has just become out of balance, a very thick layer of organic matter can develop.
Some grass species are very prone to producing a lot of thatch.
Is thatch bad for your lawn?
In moderation, a thatch layer can be beneficial to your grass as it helps retain moisture and provides some insulation to the soil. However, if it accumulates excessively, it can cause a lot of problems.
A thick layer of lawn thatch can cause:
- Water and Nutrient Problems: Thatch can create a barrier that hinders the penetration of water, air, and nutrients into the soil. It acts like a sponge, holding these essentials at the surface and preventing it from getting down to the roots. The grass roots cannot breathe properly, and the grass grows poorly. The lawn will look tired and old.
- Disease and Pest Issues: Thick thatch layers can be a haven for pests such as leatherjackets and chafer grubs. Weaker grass which is damp is also very prone to fungal diseases such as red thread and snow mould.
- Root Problems: Grass roots may be forced to grow up into the thatch layer instead of penetrating the soil. This can create a shallow root system and make the lawn more susceptible to stress in difficult times such as drought.
- Compaction: Thatch can contribute to soil compaction by limiting the movement of air and water in the soil. A soil which cannot breathe becomes lifeless, dry and roots will shrink as a result. This increases compaction risk.
Managing the depth of this layer is very important in maintaining the health of the grass in a cool-season lawn.
How much thatch is healthy?
For a healthy lawn, I recommend that a thatch layer shouldn’t be allowed to go over 10mm thick. I recommend considering thatch-reducing lawn treatments if it is more than that in your lawn.