What Is Thatch?
Thatch is a layer of intertwined organic material located between the turf and the soil. It can reach up to 4 centimetres in thickness and cause a number of problems. This layer appears when the organic debris produced by the grass builds up faster than it can be naturally broken down by the soil's biological activity. This build-up is largely explained by the presence of lignin in the various parts that make up the grass. Lignin is a biomolecule that is highly resistant to decomposition. It is a major component of wood and stiffens the different parts of a plant. In turf, the stem nodes, the crown (the base of the grass blade) and the rhizomes contain the largest amounts. That is why they are harder for soil biology to break down and therefore make up most of the thatch.
Why does thatch develop?
Thatch production is a natural phenomenon, but several factors can speed it up:
- Some grass species produce more lignin and therefore more thatch
- Acidic soil reduces the number of micro-organisms able to break down organic waste
- Certain pesticides can reduce the earthworm population, which helps limit thatch by aiding decomposition
- Excessive use of fertilizer can increase thatch production, either because it acidifies the soil or because it boosts the growth of the roots, stems and rhizomes responsible for it
- Intensive watering can slow the decomposition of thatch by reducing the activity of micro-organisms
- Too many grass clippings also encourage thatch to build up
What problems does thatch cause?
Thatch is not a problem in itself. A thin layer can protect the turf by partially insulating it, increasing its resilience and resistance to wear while reducing soil compaction. Unfortunately, in most cases the thatch layer is too thick and the drawbacks far outweigh the benefits:
- Thatch acts like a sponge and retains water, preventing proper irrigation of the soil.
- Watering in dry periods is harder and the turf is more likely to dry out quickly.
- Too much thatch makes the turf more sensitive to temperature swings
- Thatch is an area where diseases, fungi and harmful insects thrive easily
- The pesticides used to fight them are less effective because they struggle to pass through the thatch
- The mechanical operations needed to remove thatch always risk damaging the turf
- Fertilizers also struggle to get through this organic barrier
- The turf becomes more acidic and moss appears more easily