Biennial allium grown as an annual for storage bulbs. Variety choice depends as much on latitude as on hardiness zone.
Hardiness ratings
| System | Rating | Temperature range | How to read it |
|---|---|---|---|
| USDA hardiness zone | Zone 3–10 | −40 °C to 4.4 °C | Zones where it can be grown as an annual — not a frost-tolerance rating |
| RHS hardiness rating | H7 | down to −20 °C | Plant needs at least this level of cold tolerance |
| Canadian plant hardiness zone | Zone 3–9 | −34 °C and warmer | Zones where it can be grown as an annual — not a frost-tolerance rating |
| Australian (ANBG) zone | Zone 1–6 | −15 °C to 15 °C | Zones where it can be grown as an annual — not a frost-tolerance rating |
As a tender annual, Onion doesn't overwinter — the zone range shows where the growing season supports it. See the RHS rating for its actual cold tolerance.
Growing notes
- Long-day cultivars (>14 hr daylight) bulb up north of ~35° latitude; short-day cultivars (10–12 hr) suit south of ~28°; intermediate-day for the band between
- Choosing the wrong day-length type is the most common reason home-grown onions fail to bulb
Pet caution: Onion is listed as potentially harmful to cats and/or dogs. Keep pets from grazing on it, and contact a vet if you suspect your animal has eaten some.
Categories
Related plants
Cross-check Onion against your zones