Hard scarifying and dethatching (renovation)

Renovation, not routine

Routine scarifying is a light comb. Renovation scarifying is deliberately severe: on a lawn choked with thatch and moss, you take the blades down until they score the soil, and remove most of the dead material in one go. The lawn will look wrecked for a few weeks; that is expected, and it is what makes room for new grass.

How

1. Kill heavy moss with iron sulfate a week or two before, and let it blacken.
2. Mow short, to about 2–3 cm (1 in).
3. Make a first pass with the blades set to just touch the soil.
4. Make a second pass at right angles, a little deeper.
5. Rake up and remove everything. Expect a lot: several bags for a small lawn.

When

Early autumn is best, early spring second. The grass must be actively growing to recover, and the soil should be moist but not wet.

The renovation sequence

Scarify, then core aerate, then overseed, then topdress, all within a few days.