When to sow Onion (From Seed) in the UK
Onion (From Seed) is sown to the calendar rather than to the frost, so the window is much the same wherever you garden in the UK.
Sowing and harvest dates by region
Onion (From Seed) is grown to the calendar rather than to the frost, so the same dates apply across the whole UK and every region below reads the same. Where a plant’s timings do follow the frost, Plot shifts them from the Midlands and Lowland Wales baseline using Met Office average frost dates.
| Where you are | Sow indoors | Sow outdoors | Plant out | Harvest |
|---|---|---|---|---|
| South West Coast and Cornwall | early January to late February | early March to mid April | early April to early May | late July to late September |
| South Coast and Channel | early January to late February | early March to mid April | early April to early May | late July to late September |
| Greater London (Urban Heat Island) | early January to late February | early March to mid April | early April to early May | late July to late September |
| South East and Home Counties | early January to late February | early March to mid April | early April to early May | late July to late September |
| East Anglia | early January to late February | early March to mid April | early April to early May | late July to late September |
| Midlands and Lowland Wales | early January to late February | early March to mid April | early April to early May | late July to late September |
| Wales and West Coast | early January to late February | early March to mid April | early April to early May | late July to late September |
| Northern England | early January to late February | early March to mid April | early April to early May | late July to late September |
| Scotland Lowlands and Central Belt | early January to late February | early March to mid April | early April to early May | late July to late September |
| Scotland Highlands and Islands | early January to late February | early March to mid April | early April to early May | late July to late September |
| Northern Ireland | early January to late February | early March to mid April | early April to early May | late July to late September |
| Channel Islands and Isle of Man | early January to late February | early March to mid April | early April to early May | late July to late September |
Growing notes
Seed-raised onions are started far earlier than sets: sow in modules from mid-winter to early spring under cover, or direct outdoors from early to mid-spring, then space plants 5-10cm apart. Multi-sown modules of three or four seeds can be planted as a clump. Slower and fussier than sets, but a much wider choice of varieties.
At a glance
- Spacing
- 10 cm between plants
- Row spacing
- 28 cm
- Plants per m²
- 35
- Days to maturity
- 180 days
- Yield per plant
- 0.2 kg
- Sun
- Full
- Frost tender
- No
- Grows in a container
- Yes, 20 litres or more
- Minimum soil depth
- 20 cm
- Balcony rating
- 2 out of 5
What usually goes wrong
- onion white rot
- onion downy mildew
- allium leaf miner
- bolting
Companion planting
Grows well near
Keep away from
Related guides
Timings cross-checked against RHS guidance for onion (from seed).