Autumn scarifying (dethatching)

What scarifying does

Thatch is the layer of dead stems, roots and moss that builds up between the grass and the soil. A thin layer is harmless, but more than about 1 cm (⅜ in) holds water at the surface, encourages moss and disease, and stops seed, feed and water reaching the roots. A scarifier (verticutter) has blades that slice into that layer and pull it out.

When

September is ideal for cool-season lawns: the grass is still growing strongly enough to fill the gaps, the soil is moist, and weeds are less likely to move into the scratched areas. Do it on a dry day when the soil is moist but not wet.

How

1. If there is a lot of moss, treat it with iron sulfate about a week beforehand and let it blacken.
2. Mow a little shorter than usual.
3. Start with the blades set shallow and lower them only if little comes out. Make two passes at right angles.
4. Rake up and remove everything the machine brings to the surface. There is usually far more than you expect.

Straight after

The lawn will look scratched and thin for two or three weeks. That is the point at which to aerate compacted areas and overseed, while the surface is open. A light top-dressing finishes the job.