What time of day you should actually mow
Mid-morning to late afternoon, and the reason is dew. Why the first and last hours of the day are the worst, and how to find your own window.
Published 16 March 2026 ·Last reviewed 20 August 2026
The short answer: mid-morning to late afternoon. Roughly 10am to 5pm in spring and autumn, with a wider window in high summer.
The interesting part is why the edges of the day are bad, because the two ends are bad for completely different reasons.
The morning problem is dew
On a clear, still night the grass canopy radiates heat to the sky and drops several degrees below air temperature. When it reaches the dewpoint, water condenses on the leaves. That is dew, and a good dew night lays down a few tenths of a millimetre of water across the whole lawn.
Cutting through it is a bad idea for three reasons. Wet leaves bend away from the blade and tear rather than cut, leaving a ragged edge that browns off. Wet clippings clump, block the deck and land in wads that smother the grass under them. And a mower moving between wet plants is an efficient way to spread fungal disease around a lawn.
So you wait for burn-off. How long that takes is not a fixed time of day — it depends on how much dew formed and how fast the morning dries it:
- Radiation. Early sun is weak, and much of it goes into warming the canopy rather than evaporating water.
- Humidity. Evaporation cannot proceed into saturated air, and dawn air is usually close to saturated. This is why burn-off often stalls until the air warms.
- Wind. A breeze both prevents dew forming overnight and clears what did.
In UK spring and autumn that typically lands between 10 and 11am. On a bright, breezy morning it can be 8am. On a still, damp, overcast day it might not happen at all.
The evening problem is also dew
Dew starts reforming roughly two hours before sunset, as the canopy begins cooling. So the sensible finish is not sunset — it is a couple of hours before it.
There is a second reason to stop early. Grass cut late in the day goes into the night wet at the cut ends, and stays wet until mid-morning. That is a long window for disease to get established, and it is the reason evening mowing has a bad reputation in humid weather.
The neighbour problem
There is no UK law setting mowing hours. Councils act on persistent noise nuisance under the Environmental Protection Act 1990, which weighs a pattern rather than a single Sunday morning. Many councils publish advisory “considerate hours”: commonly not before 8am on weekdays, later on Sundays and bank holidays, finishing around 8pm.
Conveniently, that lines up almost exactly with what the grass wants. The hours that annoy your neighbours are also the hours that are bad for the lawn.
High summer is different
When it is genuinely hot — above about 26°C — the calculation flips. The sward is already under heat stress in the middle of the day, and cutting adds to a load it is struggling with. In a heatwave, an early-evening cut once the worst of the heat has passed is kinder than a midday one, and raising the height matters more than the timing.
In practice
Wait until the grass is dry to the touch. Finish a couple of hours before sunset. If it is over 26°C, avoid the middle of the day and raise the deck.
Find your window for today — it works dew burn-off out from the actual forecast rather than assuming a time.