How to Grow Onions
Allium cepa
Day-length-driven bulbs — choosing the right type for your latitude is everything.
About onions
Onions are a long-season cool-weather crop with one crucial quirk: bulbing is triggered by day length, so you must match the variety to your latitude. Long-day types suit northern zones, short-day types the South, and day-neutral types grow well almost anywhere. Start from seed, sets, or transplants for a pantry staple that stores for months.
When to plant and harvest onions
Timing is relative to your frost dates. Find your USDA zone for exact dates, or browse the month-by-month calendars.
Start seeds indoors
8–10 weeks before last frost
Transplant outdoors
As soon as soil is workable
Direct sow
Sets or seed in early spring
Harvest
Mid-to-late summer
How to grow onions step by step
- 1
Choose long-day (North), short-day (South), or day-neutral types to match your latitude.
- 2
Start seed indoors 8–10 weeks early, or plant sets/transplants in early spring.
- 3
Set out pencil-thick transplants 4 in apart as soon as soil can be worked.
- 4
Keep weed-free and evenly watered while bulbs size up.
- 5
Stop watering and harvest when the tops yellow and fall over.
Common problems growing onions
⚠ Small bulbs
Wrong day-length type for your latitude, or crowding/weed competition.
⚠ Bolting (flower stalks)
From cold stress on large transplants/sets — use smaller sets and avoid early cold snaps.
⚠ Rot in storage
Cure thoroughly and store thick-necked bulbs first; they don’t keep.
✓ Good companions for onions
✗ Keep away from
🧺 Harvesting onions
When most tops have flopped over and started to brown, lift the bulbs and cure them in a dry, airy place for 2–3 weeks until the necks are papery. Then trim and store.
Onions: frequently asked questions
What are long-day and short-day onions?＋
They bulb at different day lengths. Long-day onions suit northern gardens, short-day the South, and day-neutral types work in between.
Should I grow onions from seed or sets?＋
Sets are easiest and fastest; seed offers far more variety and better storage but needs an early indoor start.
Grow onions in your zone
See exactly when to plant and what else to grow alongside onions, tailored to your USDA hardiness zone.
