When to Plant Onions in Idaho
In Idaho, the time to plant onions outside runs from Mar 9 – Mar 23 in Lewiston to Apr 25 – May 9 in Shelley. In Boise City, it's Mar 27 – Apr 10. The average last spring frost differs by about 7 weeks across the state (Apr 6 in Lewiston, May 23 in Shelley), so use the dates for the town nearest you.
Onions are cold-hardy. Plant sets or transplants early so they grow leaves before long summer days trigger bulbing.
- Start indoors: 10–12 weeks before the last frost.
- Plant outside: 2–4 weeks before the last frost.
Onions planting dates in Idaho by city
| City | Zone | Start indoors | Plant outside |
|---|---|---|---|
| Ammon | 5b | Feb 14 – Feb 28 | Apr 11 – Apr 25 |
| Blackfoot | 5b | Feb 10 – Feb 24 | Apr 7 – Apr 21 |
| Boise City | 7a | Jan 30 – Feb 13 | Mar 27 – Apr 10 |
| Burley | 6b | Feb 12 – Feb 26 | Apr 9 – Apr 23 |
| Caldwell | 7a | Feb 4 – Feb 18 | Apr 1 – Apr 15 |
| Chubbuck | 6b | Feb 21 – Mar 7 | Apr 18 – May 2 |
| Coeur d'Alene | 6b | Jan 28 – Feb 11 | Mar 25 – Apr 8 |
| Eagle | 7a | Feb 5 – Feb 19 | Apr 2 – Apr 16 |
| Emmett | 7a | Feb 5 – Feb 19 | Apr 2 – Apr 16 |
| Fruitland | 7a | Jan 28 – Feb 11 | Mar 25 – Apr 8 |
| Garden City | 7a | Feb 22 – Mar 8 | Apr 19 – May 3 |
| Hailey | 6a | Feb 18 – Mar 4 | Apr 15 – Apr 29 |
| Hayden | 6b | Jan 28 – Feb 11 | Mar 25 – Apr 8 |
| Idaho Falls | 5b | Feb 14 – Feb 28 | Apr 11 – Apr 25 |
| Jerome | 6b | Feb 7 – Feb 21 | Apr 4 – Apr 18 |
| Kimberly | 6b | Feb 11 – Feb 25 | Apr 8 – Apr 22 |
| Kuna | 7a | Jan 30 – Feb 13 | Mar 27 – Apr 10 |
| Lewiston | 7a | Jan 12 – Jan 26 | Mar 9 – Mar 23 |
| Meridian | 7a | Jan 30 – Feb 13 | Mar 27 – Apr 10 |
| Middleton | 7a | Feb 4 – Feb 18 | Apr 1 – Apr 15 |
| Moscow | 6b | Feb 4 – Feb 18 | Apr 1 – Apr 15 |
| Mountain Home | 7a | Feb 7 – Feb 21 | Apr 4 – Apr 18 |
| Nampa | 7a | Feb 4 – Feb 18 | Apr 1 – Apr 15 |
| Payette | 7a | Jan 25 – Feb 8 | Mar 22 – Apr 5 |
| Pocatello | 6a | Feb 7 – Feb 21 | Apr 4 – Apr 18 |
| Post Falls | 6b | Jan 28 – Feb 11 | Mar 25 – Apr 8 |
| Preston | 6a | Feb 21 – Mar 7 | Apr 18 – May 2 |
| Rathdrum | 6b | Jan 28 – Feb 11 | Mar 25 – Apr 8 |
| Rexburg | 5a | Feb 17 – Mar 3 | Apr 14 – Apr 28 |
| Rigby | 5b | Feb 14 – Feb 28 | Apr 11 – Apr 25 |
| Rupert | 6a | Feb 11 – Feb 25 | Apr 8 – Apr 22 |
| Sandpoint | 6b | Feb 13 – Feb 27 | Apr 10 – Apr 24 |
| Shelley | 5b | Feb 28 – Mar 14 | Apr 25 – May 9 |
| Star | 7a | Feb 4 – Feb 18 | Apr 1 – Apr 15 |
| Twin Falls | 7a | Feb 5 – Feb 19 | Apr 2 – Apr 16 |
| Weiser | 7a | Jan 29 – Feb 12 | Mar 26 – Apr 9 |
Calculated from each town's average (50%) frost dates, from the nearest NOAA station (1991–2020). Typical dates for the 2027 planting season, based on NOAA's 1991–2020 averages. They are long-term odds, not a forecast: always check your local forecast before planting. Zones: 2023 USDA Plant Hardiness Zone Map (USDA-ARS and Oregon State University). Not the official map; see planthardiness.ars.usda.gov.
See all frost dates in Idaho, or the general guide to when to plant onions.
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