How high to mow your lawn through the year

The short answer

For an ordinary family lawn, the RHS gives roughly 13 to 25mm (a half to one inch) in summer and up to 40mm (an inch and a half) in spring and autumn. A fine ornamental lawn is kept much shorter, at 6 to 13mm (a quarter to a half inch), and needs a cylinder mower and a lot more attention.

Two RHS pages give slightly different wording. One gives ranges, as above. The other, its mowing how-to, says about 4cm in spring, autumn and winter and about 2.5cm in summer. They agree on the pattern: higher outside summer, lowest at midsummer, and never close-shaved for a family lawn.

Heights by season

• First cut of the year: use the highest setting. The RHS says the lawn may look scruffy and yellow at first but will green up with regular cuts.
• Spring: up to 40mm, or about 4cm. As general guidance, lower the blades in stages if you want it shorter, not in one go.
• Summer: 13 to 25mm for a standard lawn. In hot, dry weather the RHS advises raising the cutting height, especially on fine lawns, and avoiding close cutting.
• Autumn: up to 40mm again. The RHS September advice is to keep the cutting height high, which helps the grass cope with the last warm, dry spell and tolerate foot traffic when wet weather returns.
• Winter: mowing is usually unnecessary. If it is mild and the grass is still growing, mow occasionally on a high setting.

Heights by how the lawn is used

A lawn that takes football, dogs and a trampoline is better kept at the upper end of the range. As general guidance, taller grass has more leaf area to recover from wear and roots that go deeper. A lawn that is mostly looked at can be kept a little shorter, but the RHS is clear that very short cuts weaken it.

Shady areas under trees are a special case. The RHS says dry or shaded areas under trees need less frequent mowing. Cut those higher and less often than the sunny part of the lawn.

New lawns have their own rule. The RHS says to let sown grass reach at least 5cm (2in) tall before the first cut, with the blades on the highest setting. Its seeding page adds that you should lightly firm the soil when seedlings reach 5 to 7.5cm and cut two or three days later.

The one-third rule

The RHS says to take off no more than one-third of the grass height in a single cut. So if the lawn is 6cm tall and you want it at 4cm, that is exactly one-third and fine. If it has run away to 12cm after a wet fortnight, do not drop it to 4cm in one pass. Cut to about 8cm, wait a few days, then take it down in a second cut.

This is the main reason holiday returns go wrong. As general guidance, cutting a long lawn hard exposes pale, tender stem bases and can leave a scalped, stressed lawn that is then slow to recover. If long grass is a regular problem, the fix is more frequent mowing, not a lower setting.

How often to mow

The RHS says a traditional lawn may need mowing weekly or fortnightly from March to October. In spring and autumn that is once a fortnight or once a week depending on growth. In summer it is about weekly, dropping to fortnightly or less during drought. Prolonged dry spells in summer mean mowing is not necessary at all.

Let the grass decide, not the calendar. If growth has stalled in a heatwave, leave it. If it has shot up after rain, mow sooner. The RHS also says never to mow when the ground is soft, wet or frozen, or during cold, drying winds. Change direction at least every month so the grass does not lean one way and the mower does not wear ruts.

Sharp blades and clippings

The RHS says sharp, clean blades give the best cut, and that blunt blades tear the grass, which harms the lawn and looks unsightly. Rotary blades can be sharpened at home, but only with the mower switched off or unplugged. Cylinder mowers should go to a professional.

On clippings, the RHS gives a balanced view. Empty the box regularly because a full box leaves clumps. Removing clippings can help prevent some lawn fungal problems. In very dry weather, clippings under 1cm can be left on the grass to hold moisture. Its drought advice also suggests leaving small clippings as a mulch, kept small so they do not smother the grass. Clippings from a lawn treated with a selective weedkiller must be disposed of as the product label says.

Why close mowing causes thin grass and moss

The RHS is blunt about this. Cutting too short weakens the grass and encourages shallow roots, makes the lawn more vulnerable to drought, weeds and moss, and means more frequent maintenance and feeding. Very low cuts can also scalp the lawn where bumps or tree roots sit near the surface, leaving bare patches.

Its moss page lists mowing too low among the causes of sparse, weak, patchy grass that moss moves into, and tells you to check your mower's cutting height. This is why a moss problem is not solved by killing the moss alone. Raising the blades is part of the lasting fix, alongside scarifying and better drainage. Our guide to moss in lawns covers the rest.

Lawns left too long have their own problem. The RHS says they develop loose, weak growth that handles foot traffic poorly. So the aim is neither scalped nor shaggy: a steady height, cut often.

The last cut of the year

Neither RHS mowing page gives a date or height for the final cut. What they do say is that winter mowing is usually unnecessary and that you should only mow on mild days. The RHS October advice is to mow only if needed, in mild weather, and set the blades slightly higher than in summer, because grass keeps growing above 7 degrees Celsius.

As general guidance, make the last cut when growth slows, on a dry day, on a high setting, and clear fallen leaves from the grass so it is not smothered. Newly sown areas are the exception: the RHS says they should be mowed once to thicken them before winter, with the blades at 5cm or higher.

If you are planning scarifying or overseeding, mow on a high setting just before. Our autumn lawn restoration timetable shows where mowing fits. If you would rather hand the regular cutting over, see our lawn maintenance page.