What is thatch
Thatch is the accumulation of organic matter in the base of the lawn. It consists of dead or decomposing plant shoots, roots and stems. It starts to have an adverse effect on the lawn when the grass roots grow in this layer of organic matter, rather than in the soil.
A small amount of thatch is beneficial to the overall health of the lawn. It creates a buffer zone and also improves turf resilience. It’s when the build up becomes excessive, then it has a detrimental effect on the health of the lawn.
Environmental conditions often play a large part in the accumulation of thatch. However, poor turf care practices are often the reason why levels becomes excessive. When this happens and action is not taken, then the quality and condition of the lawn is going to deteriorate. Once this happens, action has to be taken to bring the level down and restore the lawn to its former glory.
What causes thatch
The thatch layer increases when shoot production is greater than the decomposition rate. Thatch is naturally degraded by the micro-organisms in the soil. However, there are several factors that can have a negative influence on micro-organism populations and this leads to to an excessive accumulation of thatch.
- Soil type: As thatch is broken down (decomposed) by micro organisms in the soil, then soil type can play a big part here. Soils with a high sand content, by nature have a very low micro organism population. Soils with a high loam content are more likely to contain a larger population of micro organisms. These micro organisms play an important role in the breakdown of thatch.
- Soil pH: A soil that has a low pH (acidic) is likely to have a negative effect on micro organism populations. Therefore the rare of decomposition is going to be reduced.
- Over-feeding: Although fertiliser is essential to the overall health of the lawn, too nitrogen much can cause excessive thatch. This is because it produces rapid, lush shoot growth that only adds to the thatch layer.
- Over-watering: Excessive irrigation will have an influence on decomposition. The micro-organisms that decompose thatch require air to survive and reproduce. Micro-organisms can not thrive in wet soils.
- Lack of oxygen: A lack of air in the soil, caused by over-watering or soil compaction, will have an adverse effect micro organism numbers.
The effects of excessive thatch
A little thatch, up to 12mm, is beneficial to the lawn, as it creates resilience. Once the layer increase and become thicker, it starts to have a detrimental effect on the turf. Drainage is impeded, gas exchange and nutrient availability are restricted and the likely hood of pests, weeds and diseases are increased.
- Drainage is impeded: Once build up has become excessive then the lawn will become soft and spongy during wet periods of weather. Water tends to sit in the thatch layer as it has difficulty soaking through and into the soil below.
- Increased risk of drought damage: As the thatch layer accumulates, then the grass roots find it difficult to penetrate into the soil. They roots are generally confined to the thatch layer. During drought conditions this layer can become very dry, with it often being difficult to re-wet again during the drought. The inevitable then happens, as the grass becomes stressed through a lack of water. The worst case scenario is the grass dies, through a lack of moisture.
- Loss of deeper rooted grasses: The desirable grasses such as bent and fescue would be lost at the expense of shallow rooted grasses, such as annual meadow grass. Bent and fescue are the preferred grasses on golf and bowling greens, they are more tolerant to drought, turf diseases and require less feed. Annual meadow grass is a shallow rooted grass that requires additional feed and water to stay healthy. It is also very susceptible to disease and drought.
- An increase in pest and diseases: Excessive thatch will have an adverse effect on the health of the turf. Air and nutrient movement is restricted and certain turf pests and disease will become common place.
An excessive thatch layer reduces grass health and vigour, which leaves the lawn vulnerable to a whole host of pests and diseases. Once this happens remedial action needs to be undertaken, to reduce the level of thatch to an acceptable level and restore turf health.
Preventing and removing thatch
It is important to remember that thatch build up is gradual, it doesn’t happen overnight. It can be prevented with good lawn care practices, which include:
- Aerating the lawn: One of the most effective ways of preventing thatch is by aerating the lawn. Aerating helps encourage a healthy population of micro organisms, which are essential in decomposing the organic matter and preventing thatch accumulation. Hollow tine or core aeration is a great way to actually remove thatch. This type of aeration removes small plugs of turf/thatch from the lawn.
- Scarifying the lawn: Scarifying or raking physically removes thatch. A scarifier is fitted with a series of vertical blades or tines that penetrate into base of the lawn to remove thatch.
- Correct use of fertilisers: All lawns require nutrients to maintain good health. However it is important to employ a sensible fertiliser regime that avoids excessive applications of nitrogen.
- Avoid over-watering: During periods of dry weather, avoid over-watering the lawn. Generally speaking, lawns can tolerate a dry soil. It is only in extreme conditions that grass requires irrigating. If the conditions are very dry and hot, give the lawn a good soaking and let it dry out a little between soakings. Watering this way will encourage deeper rooted grasses. Avoid keeping the soil saturated. A constantly wet soil can have a detrimental effect on the microbe population, as they require air in order to reproduce and survive.
- Top dress the lawn: Top dressing the lawn with a suitable material can help dilute the thatch and improve the airspace within the root-zone. Top dressing is especially beneficial following aeration or scarification.
If you need to physically remove thatch then most effective methods are by scarifying and aerating (particularly hollow tining).