When to stop mowing for winter in the UK

Most lawn calendars say you stop mowing in October. Some say November. None of them can be right for everyone, because the grass isn't reading the calendar either.

Two things decide when a UK lawn stops growing enough to need cutting: how warm the soil is, and how long the days are. Both change through autumn, and neither changes on the same date across the country.

Soil temperature sets the pace

Turf Alert's growth model uses a published turf-science curve, the growth potential model from PACE Turf, which treats growth as a bell curve around an ideal temperature. For the grasses in most UK lawns (ryegrass, fescues and bents), that ideal is 20°C. Growth falls away on either side of it, and it falls away quickly.

Run through the same curve the model uses:

• Soil at 15°C gives about two-thirds of peak growth.
• At 10°C, about a fifth.
• At 5°C, very close to nothing.

That is why the autumn slowdown feels sudden. Soil cooling from 15°C to 10°C cuts growth to less than a third of what it was, even while the afternoons still feel mild.

Day length closes the door

On temperature alone, a mild week in December would look like growing weather. It isn't, because grass also responds to day length. The model handles this with a daylight gate: below 8 hours of daylight, a day adds no growth at all. Above 8.5 hours, there's no penalty. In between, growth is scaled down.

Both numbers were checked against real data. An earlier version of the gate pushed the model's average first mow of spring 17 days later than the real UK average, which the Woodland Trust puts at 19 March from 34,000 recorded first cuts. The current values land within a day of it, and across the 10-year backtest the model never called for a mow in December.

Here is when daylight drops below that 8.5-hour line, and then below 8 hours, using the same day-length calculation the model runs:

• Brighton: 19 November, then 2 December
• London: 17 November, then 29 November
• Manchester: 12 November, then 21 November
• Edinburgh: 6 November, then 14 November
• Aberdeen: 4 November, then 11 November

So in Aberdeen, daylight alone shuts growth down about three weeks before it does in Brighton. That's the hard stop. Cooling soil slows growth before it gets there, by an amount that changes from one year to the next.

So when is the last cut?

When a week's growth no longer adds up to anything worth cutting. In practice:

• Keep mowing while the grass is visibly growing. In a mild autumn that can run well into November in the south.
• Raise the cutting height for the last few cuts of the year. Slightly longer grass goes into winter in better shape.
• Don't mow frosted grass. Frozen blades bruise and blacken where the mower and your feet touch them.
• Stay off waterlogged lawns. Wheels and footprints compact wet soil.
• If a mild spell in winter brings growth back and the ground is firm, a light trim on a high setting does no harm.

Turf Alert does this for your location. Mow alerts spread further apart as growth slows, then stop when it does. You can see where each region stands on the UK lawn forecast, from Aberdeen to Brighton, and read more about the model on how it works.

If you'd rather not guess, sign up and your mow alerts will stop on their own when your grass does.