Crop timing
When to plant onions in the UK
The short answer, on 26 October
Yes, for overwintering onions. Autumn is the time to plant overwintering (Japanese) onion sets for a June to July harvest, and late summer to early autumn to sow Japanese onion seed indoors. Avoid heavy, waterlogged soil for autumn planting. Spring-planted sets wait until March.
“When do I plant onions” has three answers: sets in spring, seed from late winter, and overwintering onions in late summer and autumn. They are the same plant grown on different timetables.
The onion year at a glance
From Vercro's crop catalogue, a national UK calendar in whole months. The underlined month is this one. Where you live moves these edges by a few weeks either way.
| Window | J | F | M | A | M | J | J | A | S | O | N | D |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Spring-planted onions: sow indoorsFebruary to March | January: no | February: yes | March: yes | April: no | May: no | June: no | July: no | August: no | September: no | October: no | November: no | December: no |
| Spring-planted onions: sow outsideMarch to April | January: no | February: no | March: yes | April: yes | May: no | June: no | July: no | August: no | September: no | October: no | November: no | December: no |
| Spring-planted onions: plant outApril to May | January: no | February: no | March: no | April: yes | May: yes | June: no | July: no | August: no | September: no | October: no | November: no | December: no |
| Spring-planted onions: harvestJuly to September | January: no | February: no | March: no | April: no | May: no | June: no | July: yes | August: yes | September: yes | October: no | November: no | December: no |
| Overwintering: sow outsideAugust to September | January: no | February: no | March: no | April: no | May: no | June: no | July: no | August: yes | September: yes | October: no | November: no | December: no |
| Overwintering: harvestMay to July | January: no | February: no | March: no | April: no | May: yes | June: yes | July: yes | August: no | September: no | October: no | November: no | December: no |
Growing time in the catalogue: 120 days from sowing. Family: Amaryllidaceae.
What changes the answer
Sets or seed
Sets are small bulbs that establish quickly and forgive a late start. Seed is cheaper, slower and needs sowing earlier.Spring or overwintering type
Overwintering (Japanese) varieties are the ones sold for going in late in the year and cropping in early summer. Use a variety sold for the season you are planting in.Heavy soil
The RHS says autumn planting is unsuitable on heavy, waterlogged soils. There, spring sets are the safer choice.The bed’s history
Onions share white rot with garlic, leeks and shallots. See onion family rotation.
Where the sources differ
Vercro's catalogue and published advice, side by side
Vercro's catalogue sows overwintering onions directly outside in August and September. The RHS describes two different methods: sets planted in autumn, and Japanese onion seed sown indoors in late summer or early autumn. The catalogue mixes the two, and it has no entry for autumn sets.
The catalogue used to mark onions as frost sensitive, which no source we checked supports: the RHS rates the Japanese onion ‘Senshyu Yellow’ hardy through most of the UK, and its concern with cold is bolting, not frost damage. That flag was corrected on 19 September 2026.
Common timing mistakes
Planting spring sets too early in cold, wet soil
Sets sitting in cold, wet soil can rot. Wait until the soil is workable.Using spring varieties in autumn
Autumn planting is for varieties sold as overwintering. For anything else, wait for spring.Planting where onions or garlic grew last
White rot can survive in soil for at least 15 years, which makes rotation a slow-down, not a cure.Not curing before storing
Onions for storing need drying off after lifting. Damp necks rot in store.
How Vercro handles this in a real garden
In the Vercro Garden plan, overwintering onions are offered for an empty bed in late summer as a crop that stands through winter, not ruled out for missing the first frost. Spring onions and sets appear when their window opens.
Each bed keeps a record of what grew there, so the onion family's last spot is known when you plan the bed again.
Frequently asked questions
Keep going
Where this comes from
Crop windows, growing times and plant families come from Vercro's own curated crop catalogue, the same data the Vercro app uses. Where a published source says something different, we show both rather than choosing the convenient one. Reviewed 19 September 2026.
- Onions: grow your own, Royal Horticultural Society. Read 19 September 2026.
- Onion white rot, Royal Horticultural Society. Read 19 September 2026.
Keep spring and autumn onions apart
Add each planting to its bed. Vercro keeps sets, seed and overwintering onions as separate plantings with their own dates.