What to Sow in September: Vegetables, Herbs & Flowers to Plant Now

September is the hinge of the gardening year. For about three weeks the soil is still summer-warm while the air has turned autumnal — the best germinating conditions of the whole season, paired with weather that no longer scorches a seedling by lunchtime. After roughly the third week that advantage closes fast, and sowing moves indoors, into a cold frame or under a cloche. So September is really two months in one, and knowing which half you are in decides everything. Here is exactly what to sow in September, in the order you should do it.

• Early September last outdoor sowings — move fast
• Late September under cover, cloches & cold frames
• The big win overwintering sowings for an early 2027
• September rule sow for spring, not for a September harvest

What changes in September

Two clocks are running. Soil temperature lags air temperature by two to three weeks, so a bed that felt like August on the 1st still germinates seed happily on the 15th. Day length, meanwhile, has already dropped below twelve hours in most of northern Europe, and below about ten hours of daylight plants effectively stop making new growth — the so-called Persephone period. Anything you sow after mid-September will germinate, make a small plant, and then wait until February.

That is not a failure. It is the entire point. A young plant sitting through winter with roots already down flowers or crops four to six weeks earlier next year than anything sown in spring, and does it on a bigger frame. September sowings are an investment, and they pay in May.

Vegetables to sow in September

• Salads, the whole first half of the month — lettuce is at its easiest now; long days are gone so nothing bolts. Cos types and hardy butterheads carry furthest into the cold. Our full guide to growing lettuce from seed covers the autumn timings in detail.
• The hardy salad backbone — corn salad, winter purslane, rocket, chicory and endive. These four shrug off frost and are the reason a cold frame is worth having.
• Fast leaves under cover — spinach, chard, mizuna, pak choi and mustard greens. The whole Asian greens range is at its best in the first fortnight; see growing mustard greens.
• Quick roots, first week only — a final short row of radishes or turnips will finish under fleece.
• Sown now, eaten in May — overwintering spring onions, onions from seed, hardy broad beans and round-seeded peas. Late September to mid-October is the classic window and it produces the earliest crops of the following year.

Anything from the fast-growing range still has time in week one, and everything tagged for the month sits in the September sowing collection. The vegetable sowing calendar shows every window at a glance.

Herbs to sow in September

Herb sowing narrows sharply this month, but what remains is worth doing. Parsley sown in the first week germinates in a fortnight and stands all winter under a cloche. Chervil is genuinely an autumn herb — it dislikes spring warmth and is happiest sown now. Coriander makes leaf rather than seed in shortening days, and dill gives one last tender flush indoors. Watercress keeps going in a damp pot on a cool windowsill. Skip the Mediterranean woody herbs entirely: basil, rosemary and thyme want spring. Browse the full herb range and check the herb sowing calendar.

Flowers to sow in September

This is where September quietly outperforms every other month. Hardy annuals sown now germinate in warm soil, build a rosette before the cold, and flower earlier and on far larger plants than a March sowing — the technique is covered fully in our guide to autumn-sown hardy annuals.

• Hardy annuals for early cutting — nigella, larkspur, cornflowers, ammi, calendula and poppies, all sown where they are to flower.
• Sweet peas, the traditional autumn sowing — sweet peas sown in September in deep pots and overwintered in a cold frame make root systems no spring sowing can match.
• Biennials, the last honest call — foxgloves, wallflowers, sweet william, hollyhocks and forget-me-nots. Early September only, and expect smaller plants than an August sowing — we set out exactly what to expect in sowing foxgloves in September.
• Perennials with a head start — scabiosa and delphiniums sown now root before winter; several perennial and wildflower species actually need the cold to break dormancy, so an autumn sowing does the stratifying for you.
• Winter and spring colour — pansies and violas sown early in the month flower from late winter; see growing pansies from seed.

A September afternoon: the order to work in

1. Clear and assess Pull spent beans, courgettes and bolted salads. Every empty bed is a decision: sow, green-manure, or mulch.
2. Save seed before you sow Dry weather in early September is the moment for collecting your own seed — once it rains, the window shuts.
3. Sow the salads first These are the most time-critical. Short rows, shallow drills, into soil raked to a fine tilth.
4. Then the flowers Hardy annuals direct where they will flower; sweet peas and biennials into deep pots for the cold frame.
5. Cover anything left bare A green manure such as phacelia or white mustard beats bare soil all winter.
6. Get the covers on Cloches, fleece and cold frames from mid-month. Two degrees is often the whole difference.

Early September or late September?

Common September sowing mistakes

• Treating it as an extension of August — the light budget has changed. Long-season crops sown now will not finish; put those packets away properly instead (see storing seeds).
• Leaving the biennials to October — foxgloves and wallflowers sown after the first week rarely make a plant big enough to flower well next summer.
• Sowing sweet peas too shallow — they need depth for the root run. Root trainers or deep pots, not module trays.
• Watering as though it were July — cool, damp soil plus overwatering equals rot. Cut back sharply from mid-month.
• Overwintering under sealed cover — unventilated cloches breed grey mould. Open them on mild days.
• Leaving beds bare — five months of winter rain leaches nutrients and compacts the surface. Sow a green manure or mulch.

Frequently asked questions

Is it too late to sow seeds in September?
No, but the list is specific. Hardy salads, oriental greens, spinach, hardy annual flowers, sweet peas and overwintering onions, broad beans and peas all do well. What no longer works is anything needing a long warm season — tomatoes, squash, sweetcorn, French beans.

What can I sow in September for winter?
Corn salad, winter purslane, rocket, chicory, endive, mizuna, pak choi and hardy lettuce, all under a cloche, fleece or cold frame. Growth is slow from November, so think of them as a standing larder you harvest from rather than a crop that keeps growing.

Should I sow hardy annuals in September or wait until spring?
September, if you can. Autumn-sown hardy annuals flower four to six weeks earlier on much larger plants. The one caveat is heavy, wet soil, where losses over winter can be high — there, sow into pots and overwinter in a cold frame, or wait for March.

What should I do with empty beds in September?
Either sow something (salads, green manures) or cover them. Bare winter soil loses nutrients and structure. A green manure is the cheapest soil improver there is, and raised beds in particular benefit from a winter cover crop.

September asks you to garden for a season you cannot see yet. Nothing you sow this month will impress anyone in October — and then in May, while everyone else is pricking out seedlings, you will be cutting sweet peas. Browse all our vegetable seeds and flower seeds, look at the organic range, or work through the rest of our growing guides. If you sow two things this month, make them a row of corn salad and a pot of sweet peas.