PlantSowGrow
How to grow Onion (Ailsa Craig, from Seed)
Allium cepa
A big, mild, golden show onion grown from seed — cheaper than sets and the way to grow real whoppers. Best eaten by Christmas.
At a glance: Sow mid March to early April, harvest from late July.
When to sow, plant and harvest
Timed for a typical UK garden (last frost mid-April). The app uses your own town's frost dates.
Growing Onion (Ailsa Craig, from Seed): what it needs
- Light
- Full sun · 6+ hours a day
- Watering
- Water regularly in dry weather
- Soil
- Fertile, well-drained soil
- Spacing
- 10 cm, rows 30 cm apart
- In pots
- Best in the ground
- Feeding
- A general feed before sowing or planting
- Harvest
- About 150 days from sowing
- Hardiness
- USDA zones 3–9
- Difficulty
- Easy
Step by step
- Mid March – early April · 5 weeks before the last spring frost
Sow Seeds Outdoors
Sow thinly in drills where they are to grow. Sow in modules, 4–6 seeds per cell, and plant out the little clumps without splitting them.
- 10–21 days after “Sow Seeds Indoors” · Late March – early April
Check Germination
Seedlings should appear in 10–21 days. If sown outdoors, thin to 10 cm, rows 30 cm apart apart when big enough to handle.
- 21–35 days after “Plant Out” · Mid April – late April
Weed and Water
Hoe off weeds between rows and water in dry spells — even moisture gives better crops.
- 129–150 days after “Check Germination” · Late July – mid August
Start Harvesting
When the leaves flop and yellow, ease the bulbs with a fork and leave them on the surface to dry in the sun.
- 21–51 days after “Start Harvesting” · Mid August – mid September
Finish and Clear
Dry the bulbs for two weeks until the skins rustle, then store in nets somewhere cool and airy.
