Sow indoors
January – February
Sow direct
March – April
Plant out
March – April
Harvest
July – September
Days to maturity
120–120 days
Position
Full sun
Frost sensitive
No
Min soil temp
5°C
Sowing and planting calendar
| Method | From | To | Notes |
|---|---|---|---|
| Plant sets (spring) | March | April | Push sets into firm soil, tip just showing. The most reliable method in Ireland. |
| Plant sets (autumn) | September | October | Overwintering varieties for an earlier harvest the following summer. |
Regional variation: Firm, well-drained soil matters more in Ireland than exact timing — heavy, waterlogged ground produces poor bulbs regardless of when you plant. Raised beds help significantly in wetter areas.
Growing tips
Sets vs seed
Sets (small bulbs) are quicker and easier than seed — ready to harvest 2–3 weeks earlier and no thinning required. Seed gives more variety choice and is cheaper for large quantities.
Firm soil is essential
Onions need firm, well-drained soil. Loose, rich soil produces lots of top growth but small bulbs. Avoid fresh manure.
Stop watering before harvest
Once the foliage starts to yellow and fall over, stop watering. This helps the bulbs ripen and improves storage life.
Cure before storing
After lifting, lay onions on wire mesh in a warm, dry place for 3–4 weeks until outer skins are papery. Only store firm, dry bulbs.
Common problems
Onion fly
Maggots tunnel into the base of plants, causing yellowing and collapse.
Fix: Grow under insect-proof mesh. Avoid growing in the same spot as last year. Sets are less susceptible than seedlings.
White rot
ACT NOWFluffy white fungal growth at the base of plants. Persists in soil for 20+ years.
Fix: No cure. Remove and destroy affected plants. Do not grow alliums in that spot for many years.
Downy mildew
Grey-purple mould on leaves in cool, wet weather.
Fix: Improve airflow. Avoid overhead watering. Choose resistant varieties where available.
Frequently asked questions
Should I grow onions from seed or sets in Ireland?
Sets, for most growers — more reliable in Ireland's often wet spring weather, with an earlier harvest and no thinning required.
When should I harvest onions in Ireland?
When the foliage yellows and falls over naturally — usually July to September.
How do I store onions?
Cure in a warm, dry place for 3–4 weeks until the outer skins are fully papery, then store in nets in a cool, dry shed.
Related guides
Keep track of your onions in Vercro
Add your onions to a bed and each morning Today shows the jobs that matter for them, from when they went in and your local forecast. The Record keeps what you lifted.
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