How to grow Onion in the UK
Allium cepa
Onion (Allium cepa) is a vegetable that grows well in UK gardens. Sets are easier than seed for first-timers. Birds may pull them up — net the bed. This guide covers when and how to sow Onion, the soil and position it likes, watering and feeding, companion planting, and when to harvest.
When to sow & grow Onion
Sowing and harvest window through the year (UK):
Jan | Feb | Mar Plant | Apr | May | Jun | Jul Harvest | Aug Harvest | Sep Harvest | Oct | Nov | Dec |
Soil, position & care
- Soil
- Fertile, free-draining soil enriched with garden compost
- Soil pH
- 6.5–7.0
- Position
- Open, sunny site
- Sowing depth
- Tip just showing
- Spacing
- 10 cm apart, rows 30 cm
- Sowing
- Plant sets Mar–Apr (or autumn for over-wintering types)
- Growing
- Keep weed-free; stop watering as bulbs swell
- Harvest & upkeep
- Harvest when tops flop and yellow; dry in the sun before storing
- Watch for
- Onion fly, white rot, downy mildew
Companion planting for Onion
Grows well with:
Keep apart from:
Add Onion to your free 12-month plan and get watering & sowing reminders — no sign-up needed.
Onion FAQs
What grows well with Onion?
Onion grows well alongside Beetroot, Broccoli, Brussels Sprout, Cabbage, Carrot, Cauliflower. Good companions can deter pests, attract pollinators or make better use of space.
What should you not plant near Onion?
Keep Onion away from Asparagus, Asparagus Pea, Broad Bean, Dwarf French Bean, Lupin, which can compete with it or share pests and diseases.
How much sun does Onion need?
Onion prefers full sun (6+ hrs direct).
When is Onion ready to harvest?
Onion is typically ready to harvest in July, August, September in the UK.
Is Onion easy to grow?
Easy — good for beginners. Sets are easier than seed for first-timers. Birds may pull them up — net the bed.