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Key September garden jobs in the Chilterns: start lawn renovation, plant spring bulbs, divide perennials, sow winter vegetables, harvest fruit, and tidy borders. September is the start of the autumn planting season, often the best month of the year for gardening in the Chilterns. The soil is warm, the rain is returning, and plants establish quickly before winter.
Why September Is the Best Planting Month
September is often the best month of the year for gardening. The soil is warm from the summer, the rain is returning, and the air is cooler. Plants establish quickly before winter, and the gardener can work comfortably without the heat of August. In the Chilterns, September typically sees temperatures of 16 to 19 degrees Celsius and 50 to 60mm of rain, which is ideal for new plantings.
September is also the start of the autumn planting season, which runs from September to November. Autumn planting is better than spring planting for most trees, shrubs and perennials because the soil is warm enough for root growth through October and November, giving plants a head start on spring-planted specimens.
Lawn Care in September
September is the best month for lawn renovation. The soil is warm, the rain is reliable, and the grass has time to establish before winter.
- Scarify to remove thatch and moss.
- Aerate with a hollow-tine or solid-tine aerator to relieve compaction.
- Top dress with a 70/30 sand and soil mix.
- Overseed with a seed mix suited to your conditions.
- Apply an autumn lawn feed (low nitrogen, high potash).
- Treat moss with iron sulphate if needed.
See our lawn renovation guide for a full programme. Use our lawn planning tool for a CGM Care Level assessment.
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Planting Spring Bulbs in September
September is the start of the spring bulb planting season. Plant daffodils, crocus and alliums now. Wait until November for tulips (they prefer cooler soil).
- Daffodils: plant in September, 10 to 15cm deep, 10cm apart.
- Crocus: plant in September, 5 to 8cm deep, 8cm apart.
- Alliums: plant in September, 10 to 15cm deep, 15cm apart.
- Tulips: wait until November. Plant 10 to 15cm deep, 10cm apart.
- Hyacinths: plant in September, 10cm deep, 15cm apart. Wear gloves, they can irritate skin.
Plant bulbs in drifts of 7 to 15 for natural-looking groups. Avoid single rows, which look unnatural.
Dividing Perennials in September
September is a good month to divide overcrowded perennials. The soil is warm, the rain is returning, and divisions have time to establish before winter.
- Lift the clump with a fork.
- Divide into 3 or 4 sections with a spade or knife.
- Discard the tired centre, replant the vigorous outer sections.
- Replant at the same depth, water well, and mulch.
Divide: hardy geraniums, astrantia, hostas, daylilies, phlox, sedum, ornamental grasses. Do not divide: oriental poppies, echinops, monkshood (they have tap roots and do not divide well).
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Planting in September
- Plant new perennials. They will establish before winter and get off to a fast start in spring.
- Plant container-grown trees and shrubs. Water well.
- Plant strawberry runners for next year's crop.
- Plant autumn onion sets for early harvest next year.
- Plant spring cabbage and other winter vegetables.
Sowing in September
- Sow winter lettuce and salad crops under cover.
- Sow spinach for winter cropping.
- Sow overwintering onions.
- Sow green manures (phacelia, mustard, field beans) on empty beds.
- Sow hardy annuals (sweet peas, calendula, cornflower) for early flowers next year.
Harvesting in September
September is the main harvest month for fruit and vegetables.
- Apples and pears: harvest as they ripen. Test by lifting the fruit gently, if it comes away easily it is ready.
- Autumn raspberries: pick daily.
- Blackberries: pick as they turn black.
- Tomatoes: harvest before the frost. Ripen green ones indoors.
- Maincrop potatoes: harvest on a dry day. Store in hessian sacks.
- Squash and pumpkins: harvest before the first frost. Leave to cure in the sun for a week.
- Onions and shallots: harvest and dry before storing.
Tidying Borders in September
- Cut back perennials that have finished flowering. Leave some seed heads for wildlife.
- Lift and store tender perennials (dahlias, cannas, gladioli) after the first frost.
- Cut back diseased or mildewed growth to reduce overwintering problems.
- Clear fallen leaves from borders. Compost them or use as leaf mould.
- Apply a mulch of compost or manure to feed the soil over winter.
Hedge Cutting in September
September is the last month to cut hedges before the bird nesting season ends and winter sets in. Most hedges can have their final trim of the year in September.
- Trim beech and hornbeam hedges for the last time this year.
- Trim evergreen hedges (yew, box, privet, leylandii).
- Do not cut native hedges (hawthorn, blackthorn) until January or February.
See our hedge cutting guide for detail.
Common September Mistakes
- Not planting bulbs early enough. Daffodils and crocus need to be planted in September or October for spring flowers.
- Cutting hedges too late. New growth will not harden off before frost. Cut by mid-September.
- Not harvesting fruit. Windfall apples should be picked up daily to prevent disease.
- Not tidying diseased leaves. Blackspot on roses and mildew on perennials will overwinter if you do not clear affected leaves.
- Not watering new plantings. September can still be dry. Water new plants weekly.
Frequently Asked Questions
Can I plant in September?
Yes, September is one of the best months for planting. The soil is warm and the rain is returning. Plant trees, shrubs, perennials and bulbs now.
When should I scarify my lawn?
September is ideal. The grass recovers quickly in the warm soil. See our scarification guide.
Should I cut my hedge in September?
Yes, mid-September is the last chance to cut hedges before winter. New growth needs time to harden off before frost.
Get Help with September Garden Jobs
If you need help with September garden jobs in Oxfordshire, Buckinghamshire, Berkshire or Bedfordshire, send us a WhatsApp with photos and we will aim to respond within 12 to 36 hours, Monday to Sunday.
Further Reading
In mature gardens, timing is critical. Established plants respond differently to seasonal work than young plants. Watch the weather forecast and adjust plans accordingly.
Put this advice into practice
Use the relevant CGM tool or follow a related guide, then send us a few photos if you would like a tailored plan.
Sources and citations
This article draws on the following sources. Specific claims are cited inline where relevant.
- CGM field records (2024-11. Site observations from gardens across Oxfordshire, Buckinghamshire, Berkshire and Bedfordshire.
- Royal Horticultural Society (2024). RHS Gardening Advice and Plant Finder. Available at rhs.org.uk.
- Met Office (2024). Regional climate averages, South East England. Available at metoffice.gov.uk.
- British Geological Survey (2024). Soil parent material data for the Chilterns and Thames Valley. Available at bgs.ac.uk.