Thatch is the layer of dead plant material that develops between the zone of green vegetation and the soil surface. If your lawn is ten years old, you most likely already have a 30-40 millimetre thick layer of thatch.

A thin layer of thatch can have beneficial effects on your lawn, providing it with a layer of insulation and resilience. But if the thatch layer exceeds 5 millimeters the function of the grass changes. As the water permeability gets worse, the roots grow closer to the surface, plus the root mass and the oxygen exchange will decrease. As a result the grass becomes less durable and can no longer withstand sports and other activities. The risk of the grass dying increases and some grass varieties cannot survive.

Removing thatch gives a dense, competitive lawn with better oxygen exchange, greater water permeability, fewer weeds and a reduced risk of disease. This makes the grass much more durable, since the root mass grows and the roots grow deeper.

Thatch removal is best done in late spring or early autumn, when the grass is growing well. Avoid removing thatch in early spring or during dry periods, since the microlife is intensive then and the unprotected roots are at a greater risk of drying out.

Before you start dethatching, or scarifying to use another word, cut the lawn short and collect the clippings. Then choose the machine and the tools that work best for your type of lawn. For grass areas under 5,000 square metres, a scarifier with or without a collector is almost always used. For larger grass areas, use a tow-behind scarifying unit. These normally have direct, integrated collectors.

A scarifier can be equipped with flail blades, which remove the thatch effectively. Their rotating blades should not go deeper into the soil than 1 to 2 millimeters, so the grass is not damaged. On sensitive areas, such as ornamental lawns, you can use the gentler method with spring tines, which should also not go deeper into the soil than 1 to 2 millimeters. The effect is lessened with flail blades.

You should use delta blades to cut off the lateral roots of the grass and to fight broadleaf weeds effectively. These blades should not go deeper into the soil than 7-10 millimetres but they are very effective. In warmer countries, scarifying with delta blades is an important way of improving the effect of watering. It ensures that the water penetrates to the roots of the grass.

When you’ve finished dethatching your lawn, remove the material that’s been pulled up. You can compost it, though it will take longer than other garden debris to break down, or put it in the garden waste bin. Then, for best results, it is a good idea to fertilise, top dress and water the lawn.