What to plant in September in the UK

Worked out for 40 cities from their own weather and frost dates, by zone.

What to sow and plant in September in the UK, by zone: frost-free, highs of 16–22 °C (London, Manchester and 30 more): broad bean, peas, onion, spinach, lettuce and 18 more; frost-free, highs of 10–16 °C (Glasgow, Belfast and 6 more): broad bean, peas, onion, spinach, lettuce and 14 more.

In the UK, September is autumn.

Frost-free, highs of 16–22 °C: London, Manchester, Edinburgh, Birmingham and 28 more

In September, on average, these cities have highs of 17 to 20 °C and lows of 10 to 15 °C, 49 to 168 mm of rain on 10 to 17 days; the day lasts 12 h 41 min to 12 h 49 min (on the 15th).

No frost in September in 10 years of data: frost-tender crops can go in too, if it is warm enough for them.

How	What	Where
sow direct	Broad bean, peas, spinach, lettuce, radish, cabbage, broccoli, Swiss chard, beet, parsley, cilantro, arugula, chamomile, daikon, dill, kohlrabi, mustard greens	all
plant sets	Onion	all
sow direct	Carrot, kale, parsnip	London, Bristol, Cardiff and 14 more
start indoors, plant out in October	Cauliflower	Brighton and Plymouth
plant sets	Shallot	London, Bristol, Cardiff and 14 more
sow direct	Turnip	Manchester, Edinburgh, Birmingham and 13 more

Compared with August: no longer sown — leek, chickpea, chicory and Brussels sprouts.

Not starting in September: tomato (March, started indoors), bell pepper (no month outdoors by these rules), zucchini (April, started indoors) and green beans (May, sown direct) — dates for Cardiff.

Ready to harvest in September in Cardiff, if sown in the right month: broad bean (June), peas (July), lettuce (July), radish (August), carrot (July), cabbage (May), broccoli (June) and Swiss chard (July).

Frost-free, highs of 10–16 °C: Glasgow, Belfast, Aberdeen, Dundee and 4 more

In September, on average, these cities have highs of 15 to 16 °C and lows of 9 to 10 °C, 68 to 119 mm of rain on 13 to 18 days; the day lasts 12 h 47 min to 12 h 52 min (on the 15th).

No frost in September in 10 years of data: frost-tender crops can go in too, if it is warm enough for them.

How	What	Where
sow direct	Broad bean, peas, spinach, lettuce, radish, cabbage, broccoli, Swiss chard, beet, parsley, cilantro, arugula, chamomile, daikon, dill, kohlrabi, mustard greens, turnip	all
plant sets	Onion	all

Compared with August: no longer sown — carrot, kale, parsnip and shallot.

Not starting in September: tomato (March, started indoors), bell pepper (no month outdoors by these rules), zucchini (April, started indoors) and green beans (May, sown direct) — dates for Glasgow.

Ready to harvest in September in Glasgow, if sown in the right month: broad bean (June), peas (July), spinach (July), lettuce (July), radish (August), carrot (July), cabbage (May) and broccoli (June).

How we work it out

For each city we use its average weather in September and the months after (highs, lows and rain for 2016–2025, ERA5 reanalysis via Open-Meteo) and its average frost dates. A crop starts in September if the month's mean temperature reaches the minimum soil temperature for germination on its card (we use the mean air temperature as a stand-in for the soil's) and if, over its first months (up to three), the average highs stay within its group's range, with no frost for crops that cannot take it. Crops started indoors count from the month they are planted out.

Temperature groups from Colorado State University Extension: cool-season crops prefer 16–27 °C and lose quality in heat; hardy ones grow in days as cool as 4 °C, semi-hardy ones from 4–10 °C (we use 10 °C); warm-season crops need days above 13 °C, and the most tender (tomato, pepper, aubergine, melon, watermelon, squash) above 16 °C, up to 35 °C. Crops the guide does not name go into the stricter group by their frost hardiness. Broad beans, which the guide does not name, count as hardy: hardy varieties are sown in autumn and overwinter (RHS). Garlic and bulbs: a month before the first frost, and later only while the ground is not frozen (as on each city's page). French beans, courgettes and outdoor tomatoes follow the RHS instead, in months without frost: French beans and courgettes sown outdoors in late May or early June, courgettes also started indoors in April or May; tomatoes started indoors from late March to early April and planted out in June where its average highs reach 16 °C.

This is a general rule from averages: your garden can be a week or two earlier or later, and a greenhouse or a cold frame brings the season forward. Greenly works out the dates for your location.

What to plant in September in the UK

Frost-free, highs of 16–22 °C: London, Manchester, Edinburgh, Birmingham and 28 more

Frost-free, highs of 10–16 °C: Glasgow, Belfast, Aberdeen, Dundee and 4 more

How we work it out

Other months in the UK