What is thatch? How can we deal with it?
What is thatch?
Thatch is the accumulation of organic residuals, consisting of, and intermingled with, dead, living or partly decomposed roots, stems and shoots, which develop between the soil surface and the actively growing green vegetation.
Thatch only becomes a problem when its density causes grass plants to grow on top of the thatch layer rather than on the soil surface.
Thatch is something which you need to control if you are to have a lush, healthy turf.
When the drainage system has been impaired by excess thatch, your turf will feel spongy underfoot and the grass will have poor drought resistance.
Thatch contains a chemical compound called Lignin which is slow to break down. Unless conditions are perfect, which they rarely are, new grass often grows more quickly than the dead material is broken down and so it builds up.
What’s more, a dense layer of thatch can harbour pests and diseases and creates optimal conditions for moss to grow, so keeping the level of thatch down is essential to maintaining the health of your lawn.
The pros and cons
A thin layer of thatch that does not exceed 10mm is considered beneficial to your lawn as it insulates the soil and increases resilience during extreme weather conditions. However, a thick layer of thatch traps surface water and deprives the grass root system of oxygen, water and nutrients.
It protects the crown of the grass plant from damage and disease while still allowing water, oxygen, and nutrients to penetrate the soil and get into the root zone.
It also prevents the soil from the drying effects of the sun and wind in the summer and from frost and cold in the winter.
On the other hand, too much of it (half an inch or more) will start to cause problems.
Counteract the thatch
Scarifying and raking physically removes thatch, dead foliage and moss from your lawn.
Scarifying is important as it removes thatch from around the base of the grass plants which allows are, water and nutrients back into the soil.
Raking controls the build-up of thatch by removing dead foliage and growth from the surface.
The best scarifiers often have changeable cartridges with vertical blades for dislodging thatch and spring tines for controlling thatch and moss from above the surface.
It’s important that you choose the right time to scarify and this guide shows you how to scarify a lawn, step-by-step.
What causes excessive thatch?
Thatch increases when the rate of shoot production exceeds the rate of decomposition.
There are several influential factors which will contribute to, or accelerate, an increase in thatch levels and, consequently, management practices will vary from club to club depending on resources, cultural practices and ultimately, the knowledge and experience of the manager. One or several of these factors may be linked i.e. soil characteristics, grass species, soil pH, nutrient input, irrigation practices, and microbial populations.
Soil greens, or push-up greens as they are often described, retain nutrients longer, generally have a higher CEC and microbial counts. Nonetheless, they are still vulnerable to thatch accumulation, although this is more likely as a result of compaction, reduced oxygen supplies to the root system, or excessive nutrient input.