What to Sow in September UK

September is the UK's most underrated sowing month. While most gardeners pack away their seed trays, the soil is still warm, the rain is returning, and everything you sow now will crop through winter or give you a head start next spring. The key is knowing what works and what is already too late. Here is exactly what to sow in September across the UK, from salad leaves that beat supermarket prices to hardy flowers that bloom weeks ahead of spring-sown equivalents.

Vegetables to sow in September

The vegetable sowing window in September is narrower than summer, but what you put in now fills the gap between last summer harvests and the first spring crops. The first half of September gives the best results because the soil is still holding summer warmth and daylight is long enough for germination.

Winter salads are the easiest win. Lamb's lettuce, rocket, winter lettuce varieties like Winter Density and Arctic King, mizuna and mustards all sow happily in early September and crop through autumn and into spring. Under a cloche or fleece tunnel they keep going through the coldest months. A single packet of winter salad seeds costs a couple of pounds and produces leaves through the period when a supermarket bag costs £2.

Spinach and chard sown now give you leaves by October and a heavy flush the following March. Spinach bolts in summer heat, so September sowing avoids that problem entirely. Spring onions of the White Lisbon Winter Hardy variety sit through winter and are ready before any spring-sown batch. Hardy radishes (China Rose, Mooli) sow now for pulling later, and turnips sown in early September give small tender roots plus useful greens.

The real prize is spring cabbage. Sown in the first half of September, planted out in October, it grows quietly through winter and gives you fresh greens in April when nothing else is ready. It is one of the most satisfying crops in the UK gardening calendar because it fills the hungry gap when the cupboard is bare.

See our guide to vegetables to sow in August and autumn for the earlier sowing window.

What to plant out in September

Planting is as important as sowing this month. Garlic goes in from late September through early November. The bulbs need a cold spell to split into proper multi-clove heads, which is why autumn planting produces far better bulbs than spring planting. Popular varieties sell out fast, so order early. garlic bulb sets from garden suppliers sell out by mid-October.

Autumn onion sets go in from late September into October for a harvest weeks ahead of spring-planted ones. Overwintering broad beans (Aquadulce Claudia) can go in from late September in milder southern areas, though October is the safer window in the north. Strawberry runners planted now establish through autumn and crop properly next summer instead of sulking.

If you are building or extending raised beds for autumn planting, our guide to the best compost for vegetable gardens covers what soil mix works best for autumn crops.

Flowers to sow in September

Hardy annuals sown in September flower weeks earlier and grow noticeably stronger than the same seed sown next spring. They make root through autumn and are ready to romp away as soon as conditions improve in March. Calendula, cornflower, larkspur, ammi, nigella and poppies all suit an autumn sowing, either direct into cleared ground or in modules to plant out later.

Sweet peas sown in September and overwintered in a cold frame or unheated greenhouse produce longer stems and earlier flowers than spring-sown plants. If you are creating a wildflower patch, autumn sowing suits native perennial mixes because many need a cold spell before they germinate.

September is also spring bulb month. Daffodils, crocus and alliums go in now. Tulips are the exception, so leave them until November when the soil is colder to reduce the risk of tulip fire.

September lawn jobs

September beats spring for lawn work, and most gardeners miss it. The soil is warm enough for fast germination but the weather is cooler and damper, so new grass establishes without the drought stress that hits spring sowings. If you are sowing a new lawn or overseeding bare patches, this is the month to do it.

It is also the right time to scarify out thatch, aerate compacted areas, top dress with a sandy loam mix, and apply an autumn lawn feed. Autumn feed is high in potash and phosphates rather than the nitrogen of spring feed, which toughens grass for winter instead of pushing soft growth that gets damaged by frost.

What NOT to sow in September

Being honest about what will not work saves seed and disappointment. Tender crops are finished: no more courgettes, beans, sweetcorn, cucumbers or squash. Carrots and beetroot sown outdoors now will not amount to much. Most brassicas other than spring cabbage are too late.

There is a real north-south split this month. A September sowing in Cornwall and the same sowing in Aberdeenshire are not remotely the same gamble. Gardens in the north or at altitude should treat the first half of September as the whole month. When in doubt, sow into modules using a seed tray set or under cover rather than open ground, because a cloche is worth about three weeks of growing season.

Other September garden jobs

Clear finished crops as they come out rather than leaving beds to weed over. Sow a green manure such as field bean seed, rye or phacelia on bare soil, or mulch with compost. Green manure holds nutrients that would otherwise wash out over winter, protects the soil surface from heavy rain, and gets dug in or cut down in spring. If you garden no-dig, a thick autumn compost mulch does the same job while worms do the work for you over winter.

Now is also the ideal moment for soil improvement, because anything added in autumn has all winter to break down. Lift and dry onions and maincrop potatoes, cut down blighted foliage, bring in tender herbs, and start collecting leaves for leaf mould as they fall.

Frequently asked questions

What vegetables can I sow in September in the UK?

September is ideal for sowing winter salads (lamb's lettuce, rocket, winter lettuce), spinach, chard, spring onions, hardy radishes, turnips, and spring cabbage. The soil is still warm and the first half of the month gives the best results.

Can you sow grass seed in September?

September is actually the best month of the year for sowing a new lawn or overseeding bare patches in the UK. The soil is warm enough for fast germination, but cooler weather and damper conditions mean new grass establishes without the drought stress of a spring sowing.

What flowers should I sow in September?

Hardy annuals sown in September flower weeks earlier than spring-sown equivalents. Calendula, cornflower, larkspur, ammi, nigella and poppies all work well. Sweet peas sown in September and overwintered in a cold frame produce longer stems and earlier blooms.

What should I NOT sow in September?

Tender crops like courgettes, beans, sweetcorn, cucumbers and squash are finished for the season. Carrots and beetroot sown now outdoors will not produce much. Most brassicas other than spring cabbage are too late. Northern gardens should treat the first half of September as the whole month.

When should I plant garlic in the UK?

Garlic goes in from late September through to early November. The bulbs need a cold spell to split into proper multi-clove heads, which is why autumn planting gives far better results than spring planting. Order popular varieties early, as they sell out fast.

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Last reviewed: August 25, 2026 · Evidence-based content · Contains affiliate links