How to Grow Onions: Sets, Seeds and Transplants to Harvest
How to grow onions: short-day vs long-day varieties, when to plant, sets vs seeds vs transplants, spacing, fertilizer, watering, bolting, harvest, curing and storage.
Onions are easy to grow once you pick the right day-length type for your latitude. Onions start forming bulbs when days reach a certain length: short-day onions suit southern regions, long-day onions suit northern ones. Plant the wrong type and you get small bulbs or none at all.
Choose the Right Type
- Short-day (bulb at 10–12 hours of daylight): southern US zones 7–10, Mediterranean, subtropics; usually planted in autumn.
- Intermediate-day (12–14 hours): middle latitudes, zones 5–7.
- Long-day (14–16 hours): northern US, Canada, UK and northern Europe; planted in spring.
Sets, Seeds or Transplants
- Sets (small dormant bulbs): easiest, quickest; more likely to bolt if large.
- Transplants (young plants): good results, widely sold for short-day types.
- Seeds: cheapest, most variety choice; start indoors 8–10 weeks before planting out.
Planting
Plant sets 2–3 cm (1 in) deep with the tip just showing, 10 cm (4 in) apart in rows 30 cm (12 in) apart. Transplants go 10–15 cm apart, about 2–3 cm deep. Onions need full sun and loose, fertile, well-drained soil.
Feeding and Watering
Feed nitrogen during early leafy growth, then stop when bulbs begin to swell. Keep soil evenly moist, about 2.5 cm (1 in) of water a week, and stop watering when the tops start to fall over.
Harvest and Storage
Harvest when most tops have fallen over, cure for 2–3 weeks in a dry, airy place, then store cool and dry. Pungent varieties store much longer than sweet onions.
All Onion Growing Guides
- When to plant onions
- Short-day vs long-day onions
- Onion sets vs seeds and planting
- Why onions bolt
- When to harvest and cure onions
- How to store onions
- Why onions stay small
- Onion fertilizer
- Onion pests and diseases
Frequently Asked Questions
How long do onions take to grow?
About 90–120 days from sets or transplants; longer from seed and for overwintering types.
Do onions need full sun?
Yes, at least 6–8 hours a day.
Can you grow onions from a store-bought onion?
Replanting a sprouting onion gives green tops and possibly seeds, but not a good new bulb.
Can onions grow in pots?
Yes, in containers at least 25 cm deep, spaced 7–10 cm apart.
TarlaTapan guides focus on practical, field-tested growing advice. Corrections and suggestions are welcome at info@tarlatapan.tr.