What to Plant in September

Vegetables to Sow and Plant in September

September is one of the most important months in the vegetable garden. While the summer harvest is still in full swing, the focus shifts decisively towards preparing for winter and next spring. The soil is warm from summer, the days are still reasonably long, and conditions are ideal for establishing overwintering crops that will give you the earliest harvests next year. Neglect September, and you will feel it from February to April when the kitchen garden sits bare and unproductive.

Overwintering Crops

Overwintering onion sets are the single most valuable September planting. Varieties like Radar, Shakespeare and Electric Red are bred to survive British winters and produce full-sized bulbs by June — weeks ahead of spring-planted onions. Push the sets into well-drained soil so the tip just shows above the surface, spaced 10cm apart in rows 25-30cm apart. Choose a sunny, well-drained spot — onion sets sitting in waterlogged soil over winter will rot. If your soil is heavy clay, raise the bed slightly or plant in modules and transplant once established.

Garlic can go in from mid-September in southern England and the Midlands, though many gardeners prefer to wait until October or November. Early planting gives a head start on root development before winter. Choose a UK-sourced softneck variety for milder areas or a hardneck variety for colder gardens. Plant individual cloves 5cm deep, 15cm apart, with the pointed end upwards.

Spring cabbage seedlings sown in July or August should be planted out now. Space them 45cm apart in firm, well-consolidated soil — brassicas hate loose ground. Varieties like Durham Early and April are bred to stand through winter and heart up in March and April, providing fresh greens at a time when little else is available. Net against pigeons, which can strip young plants overnight.

Improving your soil for overwintering crops? Use our soil calculator to work out exactly how much topsoil or compost you need.

Green Manures

September is the ideal month to sow green manures on any bed that has finished cropping. Leaving bare soil over winter is one of the biggest mistakes a gardener can make — it loses nutrients to rain, allows weeds to colonise, and the surface compacts under winter rain.

Field beans (Vicia faba) are the best autumn-sown green manure. They fix atmospheric nitrogen in their root nodules, adding free fertility to the soil. Sow them thickly, 5cm deep, across cleared beds. They grow through winter and are chopped down and dug in during March, at least four weeks before you want to plant the bed.

Phacelia produces masses of fine roots that improve soil structure and beautiful blue flowers that attract pollinators if left to bloom. It is frost-tender, so in most areas it will be killed off by winter frosts and can simply be left on the surface as a mulch. Broadcast seed thinly over raked soil.

Crimson clover fixes nitrogen like field beans but produces a lower, denser cover. It is excellent for suppressing weeds and can be dug in during spring. It also produces stunning crimson flowers if left into late spring.

Adding organic matter when preparing beds? Our compost calculator helps you work out the right amount.

Winter Salads

September is your last chance to sow quick-growing salad crops for autumn and early winter harvesting. These hardy varieties will keep you in fresh leaves well into November, and some will survive right through to spring under cloches or cold frames.

Lamb's lettuce (corn salad) is one of the hardiest salad crops, surviving temperatures down to -15C. It grows slowly but surely through the cooler months, producing neat rosettes of mild, nutty leaves. Sow thinly in rows 15cm apart and harvest whole rosettes or pick individual leaves.

Winter purslane (Claytonia) is another remarkably hardy salad crop that thrives in cold weather. Its small, rounded leaves have a mild, slightly succulent texture. Sow directly where it is to grow — it dislikes transplanting.

Land cress tastes like watercress but grows in ordinary garden soil. It is extremely hardy and will provide peppery leaves all winter. Sow in part shade to prevent bolting.

Rocket can still be sown in early September for autumn picking. It bolts less readily as the days shorten and temperatures cool, so September-sown rocket often produces better leaves than summer sowings.

Spinach — choose a winter variety like Giant Winter or Medania. Sow in rows 30cm apart and thin seedlings to 15cm. Winter spinach grows slowly but provides valuable iron-rich leaves from November through to March if protected with a cloche.

Harvesting Your Summer Crops

The September harvest is one of the most abundant of the entire year. There is an urgency to it — nights are getting cooler, and the first frosts could arrive by late September in northern and exposed areas. Get crops in before they are damaged.

Tomatoes — pick all ripe fruit regularly. Green tomatoes that will not ripen on the vine should be brought indoors and placed in a paper bag with a ripe banana. The ethylene gas from the banana triggers ripening. Alternatively, make green tomato chutney — one of the finest autumn preserves. Cut plants down after the last harvest and compost the foliage (unless it shows signs of blight, in which case bin it rather than composting).

Runner beans and French beans should be picked every 2-3 days to keep plants producing. Once you stop picking, the plants stop flowering. Clear the plants to the compost heap once they finish cropping, but leave the roots in the soil — like all legumes, they fix nitrogen which benefits the next crop.

Maincrop potatoes should be lifted by late September. Choose a dry day, use a fork to lift the tubers carefully, and leave them on the soil surface for a couple of hours to dry before storing. Store in hessian or paper sacks in a cool, dark, frost-free place. Never store potatoes in plastic bags — they sweat and rot. Any tubers damaged by the fork should be used first, not stored.

Squash and pumpkins are ready when the stem starts to crack and the skin is hard enough that you cannot dent it with your thumbnail. Cut them with a long stem attached and cure them in a warm, sunny spot for a week or two to harden the skin further. Well-cured squash will store for months in a cool room.

Sweetcorn is ready when the tassels turn brown and a kernel pierced with your thumbnail releases milky sap. If the sap is watery, wait a few more days. If it is thick and doughy, you have left it too long. Cook sweetcorn within hours of picking for the sweetest flavour — the sugars start converting to starch the moment the cob is picked.

Quick Wins for September

• Overwintering onion sets — push them in now for the earliest onion harvest next June. Five minutes of work for months of reward.
• Green manures — scatter field bean or phacelia seed over any bare bed. It takes ten minutes and saves your soil from winter degradation.
• Lamb's lettuce — sow a row for winter salads. It survives almost anything the British winter throws at it.
• Green tomatoes — bring them indoors with a banana to ripen. Nothing goes to waste.
• Spring bulbs — plant daffodils and crocus now for colour next March. The earlier they go in, the better they establish.

Flowers to Plant and Enjoy in September

September is the pivotal month for planning next spring's display. The work you do now with bulbs, biennials and perennial divisions will determine how your garden looks from February to May. It is also the last chance to take cuttings of tender plants before the first frosts arrive.

Spring Bulb Planting

Daffodils should be planted as early in September as possible. They need a long root-establishment period before winter dormancy, and early planting gives the best results. Plant at a depth of three times the bulb's height — typically 10-15cm deep — in well-drained soil. They naturalise beautifully in grass, borders and under trees. Choose a mix of early, mid and late varieties for daffodils from February right through to April.

Crocus are one of the first signs of spring, flowering from late February. Plant corms 8-10cm deep and 7-8cm apart. They look best planted in drifts of 20 or more, either in borders or naturalised in lawns. For lawns, use a bulb planter to remove neat plugs of turf, drop in a corm, and replace the plug.

Hyacinths produce intensely fragrant, architectural spikes of bloom in March and April. Plant 10cm deep, 15cm apart. They are particularly effective in containers and window boxes where you can enjoy the scent up close. Wear gloves when handling hyacinth bulbs — they can irritate the skin.

Snowdrops and alliums — snowdrop bulbs can be planted now, though they establish best when planted "in the green" (while still in leaf) in spring. Allium bulbs should go in 10-15cm deep — the tall, architectural varieties like Purple Sensation and Globemaster add drama to late spring borders.

Do NOT plant tulips yet. Tulips should be planted in November, not September. Planting tulip bulbs in warm autumn soil increases the risk of tulip fire (Botrytis tulipae), a fungal disease that causes distorted growth and brown patches on leaves. Wait until the soil has cooled below 10C, typically in November.

Perennials and Biennials

Divide overcrowded perennials now while the soil is still warm. Lift clumps of hostas, hardy geraniums, astilbes, hemerocallis (day lilies) and Michaelmas daisies, split them into sections with a sharp spade or two back-to-back forks, and replant immediately. Water well after planting. Dividing rejuvenates tired clumps and gives you free plants to fill gaps or share with neighbours.

Plant out spring-flowering biennials that were sown earlier in summer. Wallflowers, forget-me-nots, sweet William and honesty should be transplanted to their final positions now. They will establish root systems through autumn and provide a stunning display in April and May.

Take cuttings of pelargoniums (geraniums) and fuchsias before the first frost. Take 10cm non-flowering shoots, remove the lower leaves, dip in rooting hormone, and insert into pots of gritty compost. Keep in a light, frost-free place over winter. These cuttings are your insurance policy — if the parent plants are killed by frost, you have young replacements ready for next summer.

Deadhead roses one last time to encourage a final flush of autumn blooms. Remove faded flowers back to the first outward-facing leaf with five leaflets. After this last deadheading, stop feeding roses — you want new growth to harden off before winter, not push out soft stems that will be damaged by frost.

Fruit in September

Apples — early varieties like Discovery and Worcester Pearmain are ready from early September, while the indispensable Bramley's Seedling (the king of cooking apples) is typically ready from mid to late September. Test readiness by cupping a fruit in your hand and giving it a gentle twist — if it comes away easily with the stalk intact, it is ready. Pick carefully to avoid bruising and store undamaged fruit in a cool, dark place. Wrapping individual fruits in newspaper extends storage life significantly.

Pears should be picked slightly underripe and ripened indoors. If you wait until pears are fully ripe on the tree, the flesh often turns gritty and brown at the core. Pick when the fruit is firm but starting to change colour, and ripen on a windowsill. Conference, Concorde and Williams are all at their best in September.

Plums are at their peak this month. Victoria plums — the most popular variety in British gardens — are typically ready in the first half of September. Pick when the fruit is fully coloured and gives slightly when gently squeezed. Plums do not store well, so eat, cook or freeze them promptly. A good Victoria plum tree can produce 20-30kg of fruit in a single year.

Blackberries are at their finest in September. Pick the largest, glossiest berries — they should come away from the plant easily. Avoid picking after heavy rain as the berries absorb water and lose flavour. Wild blackberries from hedgerows are free and abundant, but folklore says do not pick them after Michaelmas (29 September) — after this date they are said to have been spoiled by the devil.

Strawberry runners — if you want to expand your strawberry bed or replace older plants, peg down runners from healthy parent plants into small pots of compost sunk into the soil. Once rooted (typically 4-6 weeks), sever the runner and transplant the new plant to its permanent position. September-planted strawberry runners will establish well before winter and fruit strongly next June.

Order bare-root fruit trees now for November planting. Bare-root trees are cheaper than container-grown, establish faster, and give you the widest choice of varieties. November to March is the bare-root planting season, and popular varieties sell out quickly, so order early.

Regional Planting Adjustments

September is when regional differences in the UK start to matter significantly again. Southern gardens may enjoy mild growing conditions well into October, while northern and exposed areas could see the first frosts by late September. Plan accordingly and prioritise getting tender crops harvested and overwintering crops established.

Across all regions, the key September message is: harvest everything that is ready, sow green manures on empty beds, plant overwintering crops, and get your spring bulbs in the ground. Time spent now saves you months of bare, unproductive soil over winter.

Common September Planting Mistakes

1. Leaving maincrop potatoes in the ground too long. Slug damage increases dramatically through September as the soil stays moist and cool. Lift maincrop potatoes by late September, choosing a dry day. Slugs can tunnel into tubers and ruin an entire crop in a matter of weeks. Store in hessian sacks, not plastic, in a cool dark place.
2. Not sowing green manures on bare soil. Empty beds left uncovered over winter lose nutrients to rain, develop a hard surface crust, and become colonised by perennial weeds. Scatter field bean, phacelia or crimson clover seed over any cleared bed — it takes minutes and protects your soil all winter. Dig it in four weeks before spring planting.
3. Planting tulip bulbs too early. Tulips planted in warm September soil are highly susceptible to tulip fire (Botrytis tulipae), a fungal disease that causes brown spots on leaves and distorted growth. Wait until November when the soil temperature has dropped below 10C. Other spring bulbs — daffodils, crocus, hyacinths — are fine to plant now.
4. Forgetting to ripen green tomatoes. Do not leave green tomatoes on dying plants to rot. Pick them and bring them indoors — place them in a paper bag or cardboard box with a ripe banana. The ethylene gas released by the banana triggers ripening. Alternatively, make green tomato chutney, one of the great autumn preserves.
5. Not dividing perennials. Overcrowded clumps of perennials flower poorly and gradually die out from the centre. September, while the soil is still warm, is the ideal time to lift, divide and replant. This rejuvenates the plants, improves flowering, and gives you free plants to fill gaps elsewhere in the garden.

Frequently Asked Questions

Where to Buy Seeds and Plants in the UK

Ready to plant? These UK suppliers stock everything you need for September gardening — from overwintering onion sets to spring bulbs and green manure seeds.

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Useful Gardening Tools

Planning your September planting? These free calculators help you work out exactly how much you need.