Planting dates for sets and seed, regional timing, harvest guide, and growing tips for onions in UK gardens and allotments.
Ready to start growing? Read our full How to Grow Onions UK →
Founder & Head Grower, SoilCommander · RHS Level 2 · 12+ years growing in Yorkshire
I've been growing vegetables on my Yorkshire allotment and raised beds since 2012. Everything I write is based on what I've actually grown, failed at, and eventually got right in a real UK climate.
Watch this short guide to growing your own onions at home in the UK — covering sets vs seed, planting timing, feeding, and how to harvest and store for the best results.
🌱 Did you know? Onions need long days to trigger bulbing — which is why UK summer planting windows matter so much for getting a good-sized harvest.
Best Time to Plant Onions in the UK
Onions can be planted at two main times of year in the UK, each with distinct advantages:
🍂 Autumn Planting
When: September to November
Best for: Heat-treated sets only
Harvest: June to July (following year)
Benefits: Earlier harvest, larger bulbs
🌱 Spring Planting (Most Common)
When: March to April
Best for: All sets and seed
Harvest: August to September
Benefits: Reliable, lower bolting risk
Sowing from Seed Indoors
Growing from seed offers greater variety choice. Start seeds indoors 8–10 weeks before your intended planting date:
- January to February: Sow seeds for transplanting in April (main crop)
- August: Sow Japanese varieties for autumn transplanting
UK Planting Dates by Type
| Type | Planting Time | Spacing | Harvest |
|---|---|---|---|
| Autumn Sets | September – November | 10cm apart, rows 30cm | June – July |
| Spring Sets | March – April | 10cm apart, rows 30cm | August – September |
| Shallot Sets | February – March | 15cm apart, rows 30cm | July – August |
| Spring Onion Seeds | March – August | 1cm apart, rows 15cm | 8–12 weeks later |
Regional Timing Guide
| Region | Spring Sets | Autumn Sets |
|---|---|---|
| South England | Mid-March | October |
| Midlands / Wales | Late March | October – early November |
| North England | Early April | October (heat-treated sets only) |
| Scotland | Mid-April | Not recommended |
Harvest Timing
- Autumn-planted sets: June to early July
- Spring-planted sets: August to September
- Seed-sown onions: Late August to September
- Spring onions: 8–12 weeks after sowing, when pencil-thick
UK Growing Tips
- Soil requirements: Well-drained, fertile soil with pH 6.0–7.0. Avoid freshly manured ground.
- Sunny position: Choose the sunniest spot — onions need full sun for good bulb development.
- Bolting prevention: Avoid sets larger than 2cm diameter, and choose heat-treated sets.
- Bird protection: Cover newly planted sets with netting or fleece.
- Watering: Water during dry spells in spring and early summer, but stop 2–3 weeks before harvest.
- Crop rotation: Don’t grow onions in the same spot for at least 3 years.
Useful Tools
Hand Tools
Dibber or trowel for planting sets, garden line for straight rows, rake for soil preparation. Browse our hand tools for gardening.
Soil & Plant Care
Balanced fertilisers, pH testing kits, and insect-proof mesh. Explore our soil and plant care collection.
Related Guides
Plan Your Entire Onion Season
The UK Vegetable Garden Planner PDF gives you month-by-month sowing and harvest schedules for onions and 40+ other crops.
Get the PlannerPlan The Timing Before You Sow
Use the planting window with a planner, seed-starting setup, and the full calendar so dates stay practical for your garden.
Plan the next step
Use the printable UK Vegetable Garden Planner to turn this guide into sowing dates, bed layouts, and weekly garden tasks.