Short-Day vs Long-Day Onions: Which Should You Grow?
How day length controls onion bulbing, short-, intermediate- and long-day onions, choosing by latitude and zone, and popular varieties of each type.
Onions form bulbs in response to day length. A long-day onion grown in the south never gets enough daylight to bulb; a short-day onion grown in the north bulbs too early, while the plant is tiny. Matching the type to your latitude is the single most important choice.
The Three Types
| Type | Starts bulbing at | Where | Examples |
|---|---|---|---|
| Short-day | 10–12 hours | Below ~35° latitude; zones 7–10 | 'Texas Early White', 'Red Creole', 'Granex' (Vidalia) |
| Intermediate (day-neutral) | 12–14 hours | ~32–42°; zones 5–8 | 'Candy', 'Super Star', 'Red Stockton' |
| Long-day | 14–16 hours | Above ~37° latitude; zones 6 and colder, UK, northern Europe | 'Walla Walla', 'Yellow Sweet Spanish', 'Copra', 'Stuttgarter' |
Sweet vs Storage Onions
Sweet onions (often short-day) have high water and sugar content and store only a few weeks to months. Pungent long-day onions such as 'Copra' store 6–9 months.
More Onion Guides
- How to Grow Onions: The Complete Guide
- Onion sets vs seeds and planting
- Why onions bolt
- When to harvest and cure onions
Frequently Asked Questions
What happens if I plant the wrong onion type?
Long-day onions in the south won't bulb properly; short-day onions in the north bulb early and stay small.
Are onion sets short-day or long-day?
Most sets sold in northern areas are long-day; check the label.
TarlaTapan guides focus on practical, field-tested growing advice. Corrections and suggestions are welcome at info@tarlatapan.tr.