What is it?
Thatch is the name given to an accumulation of dead grass, decomposed grass roots, leaves mixed with some living stems and, in extreme cases, living grass roots. Thatch naturally forms in a lawn. It becomes a problem when it grows thicker, then it decays.
Thatch is the main cause of moss on lawns.
There are two types of lawn thatch; surface and sub-surface thatch.
With mowing, grass growth and seasonal changes in temperature, lawns quickly develop a layer of thatch above the soil line which encourages moisture to sit in the thatch layer.
A little surface thatch on a lawn is a good thing, it helps to hold moisture, keep the soil cool and protect the grass from drying out too quickly.
Too much surface thatch prevents the grass roots from sending roots into the soil and also creates the perfect conditions for moss. The result of excessive surface thatch is a spongy, mossy lawn.
How do you keep on top of Surface Thatch in a lawn?
Annual Scarification helps to keep thatch down to acceptable levels.
The image below shows the effectiveness Scarification has on surface thatch:
Sub-surface thatch is a layer of dead organic matter which forms a mat between where the soil line should be and the soil. Often the soil line becomes the top of the sub-surface thatch layer. This barrier makes for a very weak, prone to moss and disease lawn.
Lawns often have surface and sub-surface thatch at the same time. If a lawn has sub-surface thatch it will usually have surface thatch too.
You cannot just slice the thatch layer off the lawn, it has to be thinned out by removing vertical cores.
How can GreenThumb tell if my lawn has Sub-Surface Thatch?
We do this by removing cores from the lawn and looking at the thatch layer.
How do you thin out Sub-Surface Thatch?
Hollow-Tine Aeration, which removes thousands of plugs or cores from the lawn, is the most effective form of thinning out sub-surface thatch. For more information about Aeration, click here.
The image below shows the effect on a lawn with sub-surface thatch before and after Aeration.