The problem of thatch in lawns is sometimes overstated, but thatch in the lawn is exactly what it says! Have a look at a thatched roof next time you are out in the countryside and you will see an enlarged version of the Thatch that is to be found in lawns.
Such thatch is used exclusively to keep the water out of the house. It does the same job in the lawn. It prevents water soaking down into the soil, and in extreme cases can simply lead to the run-off of valuable rainwater from the lawn surface.
Thatch is that layer of dead and dying material just below the surface of the green sward of grass. Laying on the soil. All established lawns have it, and it is necessary to a certain extent is giving your lawn a bit of bounce.
Thatch in lawns is generally made up of horizontal stems of grass, old lawn mowings, decaying leaves and anything organic that has found its way under the green sward.
A layer of thatch with a thickness of up to 1cm (half inch) is desirable and will cause no problems. This thickness of thatch is almost necessary for your lawn to have a bit of 'body'. At this thickness, water can still penetrate down onto the soil - as can nutrients. This thickness of thatch on your lawn will also act as a mulch in drought conditions.
However, once the thatch builds up to a thicker layer - say 1 inch (2.5cms), the problems start. Rain water is impeded from percolating downwards as the thatch forms a waterproof layer. Rainwater runs off the lawn instead of finding its way down into the root zone.
The image shows a typical layer of thatch in the earth core that has been removed.
Be aware that there will be a natural - desirable - layer of decaying organic matter below the surface of the turf. This should not be confused with 'thatch' which is a denser layer of dead grass nearer to the lawn surface.
Any thickness of thatch in the lawn over the 1 cm, will also cause problems with the physical growth of the grass. The roots of the grass are obviously growing down below the thatch - into the soil, so the grass plant then has to grow up through the thatch to reach the light, and subsequently turn green. The stem of the grass which is actually growing through the thatch becomes blanched, and this soon shows through in the lawn. Thick layers of thatch effectively 'strangle' the grasses, weakening them and leaving them open to fungal attack.
There are several lawn diseases which are happy to see the presence of thatch in your lawn, for most parasitic lawn fungus disease depend upon dead matter (Thatch) either to feed directly, or as a haven for overwintering their spores - ready to emerge and cause problems in the spring.
Thatch in lawns is dealt with by raking - scarifying - in the autumn months. The operation of Aerating your lawn will also negate the problems associated with Lawn Thatch. Carried out this time of year, the grass which is left soon recovers, for this is the natural time of year for the grass to 'tiller' out and thicken up with its side shoots growth. (This is not the case in the spring, when grass is more involved in growing 'upwards'!) Lawns raked during the spring will remain weak and devoid of tillering grass growth for much of the summer, leaving quite a weak sward of grass.
Small areas of lawn can be raked free of thatch with a sturdy wire lawn rake - quite exhilarating! Larger lawns need to be tackled with a mechanical scarifyer which can be hired from most good hire centres.
Tackling the thatch in your lawn is best carried out in conjunction with removing moss which has been chemically killed a few weeks previously. The grass will obviously look thin and patchy once this operation is carried out, but will soon recover and grow much stronger as a result of the thatch removal.
If there has been a great deal of thatch removed, leaving large areas of bare soil, then these areas should be over-seeded.