What time of day you should actually mow

The short answer is mid-morning to late afternoon. Call it 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 onto the leaves. A good dew night lays down a few tenths of a millimetre of water across the entire lawn.

Cutting through that is a bad idea three times over. Wet leaves bend away from the blade and tear instead of cutting, which leaves a ragged edge that browns off. Wet clippings clump, block the deck, and land in wads that smother whatever is underneath them. And a mower moving between wet plants is an efficient way of distributing 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 overnight and how quickly the morning dries it. Early sun is weak, and much of it goes into warming the canopy rather than evaporating water off it. Evaporation cannot proceed into saturated air, and dawn air is usually close to saturated, which is why burn-off often stalls until the air itself warms. A breeze helps twice over, by preventing dew forming overnight and by clearing what did form.

In a UK spring or 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 to cool. 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, which is a long window for disease to get established. It is why evening mowing has such 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 nothing before 8am on weekdays, later on Sundays and bank holidays, finished by around 8pm.

That lines up almost exactly with what the grass wants. The hours that annoy your neighbours are the same 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 through 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 gone, is kinder than a midday one, and raising the height matters more than the timing does.

In practice

Wait until the grass is dry to the touch. Finish a couple of hours before sunset. If it is over 26°C, stay out of the middle of the day and raise the deck.

Find your window for today. We work dew burn-off out from the actual forecast rather than assuming a time.