Whenever the lawn has grown about a third above your chosen height — which in May is every five days and in August may be every three weeks. The calendar is the wrong variable.
The rule that sets the schedule
Do not remove more than roughly a third of the height in one pass. Turn that around and it becomes a frequency: if you cut at 40 mm, mow when the lawn reaches about 60 mm. How long that takes is growth, and growth is temperature, moisture and feeding.
In practice that means:
Spring, once growth starts in earnest — every five to seven days, and it is the busiest period of the year.
High summer, especially in a dry spell — growth slows or stops, and mowing a stressed lawn achieves nothing. Raise the height and leave it.
Autumn — a second flush of growth, back to weekly for a while, then tapering.
Winter — occasional topping in mild weather on ground that is not frozen or sodden, and nothing else.
Why frequent cutting is less work
Because everything scales with the material you remove. Short grass loads the blade less, uses less battery, fills the catcher more slowly and can be left on the surface rather than collected. A weekly mow at a sensible height is quicker and easier than a fortnightly one, not slower.
This is also the whole argument for a robot. A machine that removes two millimetres every day is applying the one-third rule continuously, which is why the finish after a few weeks is better than a fortnightly mow produces.
What goes wrong
Mowing on a schedule rather than on growth. A lawn cut on the first Sunday of the month is being scalped in May and shaved pointlessly in August.
How this site handles it
Nothing on this site recommends a mowing interval for your lawn, because growth is local. What the pages do is print the figures that decide how much a single session costs you — deck width, catcher volume, pack energy — and say what each one is.
The questions that keep coming in
Can I skip mowing for a holiday?
Yes, and the way to pay for it is on the return: cut high first, then lower a few days later, rather than taking the lawn back to its usual height in one pass. Two passes cost less than the check a single hard cut causes.
Does mowing more often make more work?
Less, in practice. Short grass cuts faster, loads the machine less, fills a catcher more slowly and can be left to fall rather than collected. The weekly mow is quicker than the fortnightly one it replaces.
Last reviewed 26 September 2026