When to plant onions
In zone 8, most of the UK: plant onion sets from March to April and from October to November. First harvest about 120 days later.
Growing stages
Onions: calendar by hardiness zone
| Zone | January | February | March | April | May | June | July | August | September | October | November | December |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Zone 6 | Sowing or planting | Sowing or planting, Harvest | Harvest | Harvest | Harvest | Harvest | Sowing or planting, Harvest | Sowing or planting | ||||
| Zone 7 | Sowing or planting | Sowing or planting | Harvest | Harvest | Harvest | Harvest | Harvest | Sowing or planting | Sowing or planting | |||
| Zone 8reference | Sowing or planting | Sowing or planting | Harvest | Harvest | Harvest | Harvest | Harvest | Sowing or planting | Sowing or planting | |||
| Zone 9 | Sowing or planting | Sowing or planting | Harvest | Harvest | Harvest | Harvest | Sowing or planting | Sowing or planting | ||||
| Zone 10 | Sowing or planting | Harvest | Harvest | Harvest | Sowing or planting | Sowing or planting | Sowing or planting |
- Zone 6
- −23 to −18 °C (−10 to 0 °F): high mountains
- Zone 7
- −18 to −12 °C (0 to 10 °F): upland Britain, eastern France, the Alps
- Zone 8
- −12 to −7 °C (10 to 20 °F): most of the UK and France
- Zone 9
- −7 to −1 °C (20 to 30 °F): south-west England, Brittany, Atlantic and Mediterranean coasts
- Zone 10
- −1 to 4 °C (30 to 40 °F): Isles of Scilly, the French Riviera, coastal Corsica
Indicative months. A cold year or a garden at altitude shifts everything by a month; watch the frosts too.
Onions in practice
- Spacing
- 10 cm along the row, 25 cm between rows
- Sun
- full sun
- Watering
- low
- Difficulty
- easy
- In a pot
- yes
- Support
- none
- Family
- Alliums (Amaryllidaceae)
Good companions for onions
Keep apart
Questions about onions
When to plant onions?
In zone 8: plant onion sets from March to April and from October to November. The four other zones are in the calendar above; at altitude or after a long winter, aim for the end of the window.
How long until harvest?
About 120 days after planting in zone 8, then the harvest lasts about 20 days.
How far apart?
10 cm between plants along the row and 25 cm between rows.
Can you grow onions in a pot?
Yes, in a deep enough pot, in the sun shown above. Soil dries fast in a pot: watch the watering more than in the ground.
What to plant nearby?
Good companions: beetroot, carrot, cherry tomato, corn salad, lettuce, sweet pepper, strawberry and tomato. Keep apart: broad bean, dwarf bean, climbing bean and pea.
Updated 20 October 2026, Hortipix catalogue version 1. Windows still being checked against Le Guide Clause, Vilmorin and Terre vivante (RHS and Cornell for the UK and the US), compared with OpenFarm (CC0). They remain indicative.