Most lawns that look tired in August were cut too short in June. The height of cut decides how deep the roots go, how fast the soil dries out and how much light reaches moss and weed seedlings. It is also the one lawn job that costs nothing to get right.
What height of cut suits your lawn?
British lawns fall into two camps: hard-wearing lawns sown with perennial ryegrass, and fine ornamental lawns of bents and fescues. The height follows the type:
| Lawn | Height of cut | Notes |
|---|---|---|
| Family lawn, ryegrass mix | 3.5 to 5 cm | Takes football and dogs best at this height |
| Lawn in shade | 5 cm or more | Grass needs more leaf to catch light |
| Fine ornamental lawn, bents and fescues | 2 to 2.5 cm | Needs a cylinder mower and two or three cuts a week |
| New lawn, first cuts | 5 to 6 cm | Lower gradually once it is established |
If you are not sure what you have, it is almost certainly a ryegrass mix. Cut it at 4 cm and you will not go far wrong.
How often do you need to cut to hold that height?
Often enough that no single cut takes off more than a third. For a 4 cm lawn, that means cutting at about 6 cm. In May that can be twice a week. In a dry August it might be every ten days or more.
Back from a fortnight away and the grass is at 10 cm? Do not take it straight back to 4. Cut to 6 or 7 cm, wait a few days, then go down to 4.
When should you raise the blades?
In a dry spell, and in autumn shade. Ryegrass stops growing when the soil dries out, and extra leaf shades the ground and holds on to moisture. When the Met Office forecast shows a week or more without rain, raise the cut by 1 to 2 cm and leave the clippings on the lawn. Bring it back down gradually once rain returns.
A typical British summer is cool enough for a ryegrass lawn to keep growing at 4 cm. It is the dry spells that matter, not the date.
What does the app suggest for a Manchester garden?
The example lawn is a perennial ryegrass back garden in Manchester, set to a 4 cm target. The mowing card in the calendar turns that into a height and a rhythm for the month:
In September the lawn is still growing well, so it is a weekly cut at the usual 4 cm. The height moves on its own through the year. In June and July the calendar raises the target by 20 percent for ryegrass, so 4 cm becomes 4.8 cm, with half that raise in May and August. On the dashboard, the grass height chart goes further on hot days: 25 percent up above 26°C, 35 percent above 32°C, and 1.5 cm extra when it is warm and no rain is on the way.
The app’s own base height for perennial ryegrass is 5 cm, and the height chart only flags a target more than 25 percent away from that base, so under about 3.75 cm or over 6.25 cm. A 4 cm target sits inside that range. Drop to 3 cm and the app tells you it is too low for ryegrass, which matches what a fine-turf lawn would need instead.
What else keeps the cut looking good?
- A sharp blade. A blunt one tears the tips, which turn white a day later. Sharpen or replace it every spring.
- Dry grass. Wet grass clumps and gives a ragged finish.
- Change direction. Mow a different way each time so the grass does not lean.
- Edges last. Trim the edges after mowing, not before.
Height and feeding go together, because a lawn cut at the right height uses feed better. The timing is in When to Feed Your Lawn. If you want the height for the month without looking it up, What a Green Lawn works it out from your grass, your target and the weather at your address.