Start with the one-third rule
Whatever grass you have, the rule is the same: in any single mow, remove no more than a third of the leaf. If the lawn is 6cm tall, take it to 4cm, not to 2cm.
The reason is simple. The leaf is how grass makes food. Strip most of it away in one go and the plant has to burn stored energy in the roots to rebuild, which is why a hard cut leaves a lawn yellow, thin and slow for weeks afterwards.
Heights by grass type
If you are not sure what you have, buffalo has broad, folded leaves and thick surface runners, couch is fine and wiry, and kikuyu is broad, bright green and grows over everything in its way.
- Buffalo — 2 to 5cm in full sun or light shade, and 5 to 7cm where it gets heavier shade. Buffalo in shade needs the extra leaf to gather what light it gets.
- Couch — the lowest of the three, and the one that takes a close cut best. It needs full sun to hold that finish.
- Kikuyu — mid height. It grows hard and recovers fast, but cut it low and it comes back with runners and thatch.
Higher is usually better in summer
Through a hot Central Coast summer, a slightly longer cut is a better lawn. More leaf shades the soil, so it holds moisture longer and the surface does not bake. Deeper roots follow. A thicker canopy also blocks the light weed seed needs to germinate.
Scalped short in January, a lawn dries out, thins, and gives weeds an open run.
Raise the blades again in autumn
As the days shorten, lift the cut height. Short winter days give the grass less light to work with, and more leaf means more of that light gets captured. It also gives a bit of insulation against the cold snaps that come through inland parts of the Coast.
How to recover a scalped lawn
If a lawn has been cut too hard and gone yellow, do not cut it again until there is green growth showing. Water it, give it a light feed once it is actively growing, and then bring the height down gradually rather than all at once. Warm-season grasses will come back from the runners as long as the roots survived.