September Is the Best Lawn-Repair Month of the Year, and Most People Spend It on Autumn Tidying Instead

Hampstead in north London averages 19.1°C by day and 11.1°C at night in September, with 59 mm of rain and, on average, no days of air frost (Met Office, 1991 to 2020). The RHS lists September and October as the main window for autumn lawn work, when the weather is still mild and damp. It is tempting to spend that window on planting and leaf-clearing instead, because those jobs feel more like gardening, but the lawn is the one task with a closing window this month, and it should go first.

How do you renovate a lawn in September?

Do the lawn first, because by October the RHS says sowing seed is only worthwhile in warmer parts of the UK. It also says you do not need every autumn task every year, so choose one or two that suit the lawn. Work in this order:

1. 1Mow on dry days with the blades high, so the grass copes with foot traffic when it is wet.
2. 2Scarify if you cannot see soil between the grass blades. Rake in two directions with a spring-tined rake without pulling up healthy grass, or use a powered scarifier on a large lawn. See when to scarify a lawn.
3. 3Aerate. The RHS says most lawns need it every two to three years, but clay or waterlogged soils need a hollow-tined aerator every three to four years. If your soil is heavy clay, that is the longer gap to plan for.
4. 4Top dress by brushing a soil and sand mix into the holes, which matters most after hollow-tined aerating.
5. 5Feed only if needed, with a product labelled for autumn. The RHS warns against leftover summer feed because the nitrogen encourages soft growth that disease attacks.
6. 6Sow seed on damp soil after rain so the grass establishes over autumn. When to overseed a lawn has the dates.

If a dry summer has browned the lawn, the RHS says it should recover as autumn rain and cooler temperatures arrive, and that bare patches can be repaired with seed or turf. It adds that weedkiller and fertiliser should be avoided on drought-stressed turf in autumn and left until spring if needed. For that case, skip step 5.

What should you plant or divide?

Cooler weather makes it lower risk to plant or move shrubs and trees, and the RHS says shrubs planted now have all winter to settle in. Late September is also a good time to plant new perennials, since the soil is warm and the moisture is rising.

Divide overgrown or tired herbaceous clumps such as helenium and hardy geranium now to revive them. Spring-flowering bulbs such as daffodils can go in now, since the RHS lists planting them as a September job. Tulips can wait: the RHS lists them as a November job.

Can you still trim hedges in September?

Yes, with limits. September is the first month the RSPB says is clear for hedge cutting, but it also notes that some birds breed late into September, so keep checking. The RHS suggests a final trim for evergreen hedges before winter, particularly fast growers such as leylandii, cut with the top narrower than the base to limit snow damage and shading of lower branches.

Its hedge guide, though, warns that conifers trimmed after August can develop bare patches, and that most conifers do not regrow from old wood. The two pieces of advice fit together if the trim is light, taking off new growth only and leaving the brown wood alone. When to trim a hedge covers the nest checks.

What else needs doing before the leaves come down?

• Net ponds before fallen leaves build up, as the RHS suggests, and clear fallen leaves from beds promptly. Remove diseased leaves rather than composting them, because composting can spread the disease.
• Watch for toadstools. The RHS says honey fungus fruiting bodies can appear from late September into early October, but many harmless fungi appear then too, so do not panic.
• Bring tender plants in before frost. The RHS says to watch night-time forecasts and treat below 4°C as a sign a ground frost is possible. Hampstead averages no air frost in September and a third of a day in October, so in London this is more a late-October job. The RHS advises moving fuchsias and similar plants indoors in colder areas.
• Feed hedgehogs in early autumn, when the RHS says they need to build fat reserves for hibernation, and check long grass before strimming.

What can wait?

Cutting back perennials. The RHS says to leave stems standing until late winter to shelter wildlife, removing only collapsed, mushy growth.

If September is the month you want the lawn, borders and hedge sorted but cannot find the time, our garden maintenance service covers regular visits and we take green waste away. We offer a free visit with a written quote. Previous month: August. Next: October.

Sources

• Met Office: Hampstead climate averages, 1991 to 2020
• RHS: Lawn care in autumn
• RHS: September lawns
• RHS: October lawns
• RHS: November jobs
• RHS: Lawn care for drought conditions
• RHS: September jobs
• RHS: September trees and shrubs
• RHS: September flowers
• RHS: How to trim a hedge
• RHS: Pruning hedges
• RHS: Hedgehog-friendly gardening
• RSPB: Birds' nests and nestboxes

This reflects our own read of what matters most in London and Hertfordshire gardens this month, not a guaranteed task list for yours. Soil condition and rainfall vary year to year, so use it as a guide — get in touch if you'd like a hand with any of it.