When to Plant Onions in Wyoming
In Wyoming, the time to plant onions outside runs from Apr 12 – Apr 26 in Casper to May 23 – Jun 6 in Jackson. In Cheyenne, it's Apr 16 – Apr 30. The average last spring frost differs by about 6 weeks across the state (May 10 in Casper, Jun 20 in Jackson), 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 Wyoming by city
| City | Zone | Start indoors | Plant outside |
|---|---|---|---|
| Casper | 5a | Feb 15 – Mar 1 | Apr 12 – Apr 26 |
| Cheyenne | 5b | Feb 19 – Mar 5 | Apr 16 – Apr 30 |
| Cody | 5a | Feb 17 – Mar 3 | Apr 14 – Apr 28 |
| Douglas | 5a | Feb 24 – Mar 10 | Apr 21 – May 5 |
| Evanston | 5a | Mar 20 – Apr 3 | May 15 – May 29 |
| Gillette | 4b | Feb 20 – Mar 6 | Apr 17 – May 1 |
| Green River | 5a | Mar 1 – Mar 15 | Apr 26 – May 10 |
| Jackson | 4b | Mar 28 – Apr 11 | May 23 – Jun 6 |
| Lander | 5a | Feb 23 – Mar 9 | Apr 20 – May 4 |
| Laramie | 4a | Mar 15 – Mar 29 | May 10 – May 24 |
| Powell | 5a | Feb 24 – Mar 10 | Apr 21 – May 5 |
| Rawlins | 5a | Feb 22 – Mar 8 | Apr 19 – May 3 |
| Riverton | 5a | Feb 17 – Mar 3 | Apr 14 – Apr 28 |
| Rock Springs | 5a | Mar 1 – Mar 15 | Apr 26 – May 10 |
| Sheridan | 5a | Feb 26 – Mar 12 | Apr 23 – May 7 |
| Torrington | 5a | Feb 16 – Mar 2 | Apr 13 – Apr 27 |
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 Wyoming, or the general guide to when to plant onions.
Getting beds ready? Work out how much raised bed soil, compost or mulch you need with our sister site, Yard Coverage.