The Truth about GrassCycling and Thatch
To most people, the idea of leaving loose grass clippings on the lawn after mowing means an unsightly garden or, even worse, a garden prone to thatch. However the loose clippings which result from GrassCycling (or mulching) are entirely unrelated to thatch. In fact, a mower optimised for GrassCycling is likely to eliminate any thatch already present.
Thatch is a layer of dead and living shoots, stems and roots, woven tightly together between the green blades of your lawn and its soil surface. This organic matter is high in lignin – a chemical that is resistant to microbial breakdown and is very difficult to get rid of! Thatch is caused by too much lawn growth – the grass roots and stems remain dead on the lawn surface and don't decompose quickly enough.
This can be compared to a bucket with a hole in it, from which water slowly drips. If you continue to fill the bucket, the water can't escape quickly enough and will eventually spill out over the rim. In the case of your lawn, heightened growth and restricted ability to decompose result in a layer of stems and shoots that, if left in place, will continue to restrict the growth of fresh new grass.
Whilst thatch can occur if lawns are cut with lawnmowers too much or too often, the key issue is not the blades of grass, but the roots themselves. A major cause of thatch is soil with a pH above 7.2 or below 6, or soil which is particularly heavy or salty. It has also been found that the use of powerful fungicides is a significant factor in thatch development as a result of their damaging effect on soil microbes and earthworms, which are both vital in the decomposition process.
Once thatch has taken hold, the problems for your lawn are far more than cosmetic. Thatch is a layer that actively sheds its water, creating dry spots in the soil that stop the plant from getting vital nutrients. At the same time fertiliser movement is restricted by the tight 'net' of thatch, making the purchase of expensive lawn equipment a fruitless pursuit. Finally – again as a result of its tightly woven nature – thatch is an ideal home for insects which will consume or irrevocably damage your lawn, leaving you with a garden that's dry, yellow and uneven, difficult to cut with any lawnmower and, ultimately, unattractive.
GrassCycling does not contribute to thatch. Research shows that grass roots are the primary cause of the problem, not leaves or loose clippings. The small cuttings produced by a GrassCycling mower are extremely high in water – as much as 85 per cent – and contain only small amounts of lignin, the substance that restricts the decomposition of roots, stems and crowns.
In fact, if thatch is a constant worry, evenly distributing loose grass cuttings across your lawn can be beneficial. These lawn clippings are not only high in water, but also release nitrogen and other beneficial nutrients when they decompose. Whilst these substances can't compensate for years of over-fertilisation and watering that cause thatch to occur, they can help struggling roots receive everything they need in order to flourish. Over time these grass clippings can help you reduce the thatch content of your lawn to a moderate level. If the thatch layer is less than a quarter of an inch thick, it acts like a shock absorber – instead of restricting the passage of air and fluid to and from the roots, it makes your lawn more resilient and your soil less likely to become compacted.
In conclusion, thatch can be a significant problem in lawn maintenance and should be carefully treated before it gets out of hand. However, providing that your layer of thatch is within reasonable limits, incorporating grass mulching into your garden maintenance can help to prevent future occurrences of thatch.