What to plant in September (UK)

By Sophie Sparkes · Updated August 2026 · 6 min read

September is the most underrated month in the UK gardening calendar. The soil is at its warmest of the whole year — warmer than May — the autumn rain does your watering, and seeds germinate in days rather than weeks. Here's what to sow and plant while that window is open.

Short answer: it is not too late. September is one of the two best sowing months of the UK year. Onion sets, winter salads, spinach, spring cabbage, oriental greens and hardy annuals all go in now — and most of them will be ready weeks before anything you sow next spring.

🧅 Onion sets — September's headline act

If you plant one thing this month, make it autumn onion sets. Varieties bred for autumn planting — 'Radar', 'Electric', 'Senshyu' and 'Troy' — go in from mid-September. They put down roots while the soil is still warm, sit tight through the cold, and then bulb up in early summer, weeks ahead of anything planted in spring.

Push each set into well-drained soil so just the tip shows, 10cm apart in rows 25cm apart. Two things matter more than anything else: drainage, because sets sitting in cold wet soil rot rather than root; and birds, who pull freshly planted sets straight back out — net them for the first fortnight until the roots grip.

Shallots can go in at the same time and are, if anything, more forgiving. One shallot planted now becomes a clump of six or eight by summer.

Veg to plant in September

🥬 Winter salads

Lamb's lettuce, mizuna, rocket, land cress and winter-hardy lettuces like 'Winter Density' and 'Arctic King' all germinate fast in September's warm soil. Sown now, they'll give you pickings right through winter — especially with a cloche or a layer of fleece over them.

🌿 Spinach

A September sowing of a hardy variety like 'Medania' produces leaves in autumn, pauses over the coldest weeks, then explodes back into growth in early spring — long before spring-sown spinach even germinates.

🌸 Spring cabbage

Plant out young spring cabbage plants now, 30cm apart, firmed in well. They stand through winter and produce sweet spring greens in April — right in the "hungry gap" when the veg patch is otherwise empty. Net them, or the pigeons will find them first.

🥬 Oriental greens

Pak choi, mizuna, mustards and Chinese cabbage are at their best sown in September. Sown in spring they bolt at the first warm spell; sown now, with shortening days, they grow steadily instead of running to seed. They're some of the quickest returns you'll get this month.

🌱 Chard & perpetual spinach

Sow in the first half of the month and you'll be picking well into winter, then again in spring before it finally bolts. Perpetual spinach in particular is close to unkillable — a good one if last season knocked your confidence.

🥕 Quick catch crops

There's still time for fast growers before the frosts: radishes (3–4 weeks), baby turnips like 'Milan Purple Top', and salad onions sown now for an early spring harvest.

Flowers to plant in September

• Daffodils and crocuses — September is the ideal month; they root strongly in warm soil. (Hold tulips back until November — here's why.)
• Hardy annuals — cornflowers, calendula, ammi and poppies sown directly now make sturdier plants that flower weeks earlier next summer.
• Wallflowers — plant out now while the soil is warm for a wall of scent next spring.

And two jobs worth doing

• Sow green manure (phacelia, field beans) on any bed that's finished for the year — it protects the soil and feeds it when dug in come spring.
• Take cuttings of tender favourites like pelargoniums and fuchsias before the first frost — free plants for next year.

September planting questions

Is it too late to plant vegetables in September?

No — and this is the single most common thing beginners get wrong. September isn't the end of the growing year, it's the start of the next one. Onion sets, garlic in colder areas, winter salads, spinach, spring cabbage and oriental greens all want to go in now. What has passed is the window for anything that needs a long warm run to ripen: don't sow courgettes, beans, sweetcorn or tomatoes.

What vegetables can I plant in September in the UK?

Autumn onion sets and shallots, winter-hardy lettuces and salad leaves, spinach, chard and perpetual spinach, pak choi and other oriental greens, radishes, baby turnips, salad onions, and spring cabbage plants. Green manure goes on any bed you've finished with.

Should I plant garlic in September or October?

October is the main month for most of the UK, so that's where we cover it properly — see what to plant in October. The exception is a cold or exposed garden in the north of the UK, where getting garlic in during the last week of September gives it more time to root before the ground turns cold. Garlic genuinely needs a cold spell to split into cloves, so there's no advantage in rushing it.

Is September a good time to sow grass seed?

It's the best time of the year. Warm soil, reliable rain and less competition from weeds mean September-sown grass establishes faster than anything you sow in spring. Aim for the first three weeks of the month so it roots before the first frosts.