Dethatching and scarifying: what, when and whether your lawn needs it

Walk on your lawn. If it feels like walking on a mattress - springy, soft, a bit disconnected from the ground - that's thatch: a woven layer of dead stems, runners and roots sitting between the green leaves and the actual soil. A little is fine. A lot is a sponge that soaks up your watering before it reaches soil, harbours pests and disease, and slowly lifts your lawn off its own dirt.

Who gets it

Thatch is a running-grass problem. Couch and kikuyu spread by stolons and rhizomes, and every year's growth lays down over the last - a kikuyu lawn left alone for a few years can be sitting on 5 cm of it. Buffalo builds thatch more slowly, and fescue barely at all (it clumps rather than runs). If you're not sure what you've got, identify your grass first - it decides how hard you can go.

Quick check: push a finger through the green down to soil. More than about 1.5 cm of brown springy material before you hit dirt, and dethatching will make a visible difference. Less than that, leave it be - a thin thatch layer insulates and cushions, and stripping a lawn that doesn't need it is just vandalism with a rental machine.

Dethatching vs scarifying

People use the words interchangeably; the machines don't. Dethatching rakes through the lawn with spring tines and combs out loose dead material - a firm going-over. Scarifying cuts vertical slices down through the thatch into the soil surface with steel blades - proper surgery that pulls up astonishing quantities of material and leaves the lawn looking like it lost a fight. Couch and kikuyu handle a genuine scarify and bounce back better than ever. Buffalo does not - its runners grow on the surface, so a hard scarify removes the lawn itself. Buffalo gets a light dethatch only.

When (this is the part people get wrong)

Late spring, roughly October to November in Melbourne, once the lawn is growing at full pace - because everything hinges on recovery. A scarified lawn has to regrow from what's left, and warm-season grass in November manages that in three or four weeks. Scarify in autumn and the lawn sits there, shredded and thin, all winter, with winter grass and broadleaf weeds gratefully colonising every gap. Better to do it hard once in November than timidly three times through the year.

The routine

1. Mow lower than usual first (this is the one occasion it's allowed).
2. Dethatch or scarify in two directions if it's bad. Rake and cart the debris - there will be several times more than you expect, so plan for the green bin to be full.
3. Water it in, feed it a week later, then water and mow as normal while it recovers.
4. Expect it to look rough for about three weeks. It pays that back for a couple of years.

It's also the perfect moment to aerate and topdress, since the lawn's already recovering - the full sequence is in the spring lawn care guide.

Quick answers

Does my lawn need dethatching?

Push a finger through the green down to the soil. More than about 1.5 cm of brown springy material before you hit dirt and dethatching will make a visible difference. Less than that, leave it: a thin layer insulates and cushions.

What is the difference between dethatching and scarifying?

Dethatching combs loose dead material out with spring tines. Scarifying cuts vertical slices through the thatch into the soil with steel blades and pulls up far more. Couch and kikuyu take a hard scarify; buffalo gets a light dethatch only.

When should I dethatch a lawn in Melbourne?

Late spring, roughly October to November, once the lawn is growing at full pace and can regrow in three or four weeks. Scarify in autumn and it sits thin all winter while winter grass and broadleaf weeds fill the gaps.