When to Plant Onions in South Dakota
In South Dakota, the time to plant onions outside runs from Mar 29 – Apr 12 in Sioux Falls to Apr 14 – Apr 28 in Box Elder. In Sioux Falls, it's Mar 29 – Apr 12. The average last spring frost differs by about 2 weeks across the state (Apr 26 in Sioux Falls, May 12 in Box Elder), 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 South Dakota by city
| City | Zone | Start indoors | Plant outside |
|---|---|---|---|
| Aberdeen | 4a | Feb 13 – Feb 27 | Apr 10 – Apr 24 |
| Belle Fourche | 5b | Feb 15 – Mar 1 | Apr 12 – Apr 26 |
| Box Elder | 5b | Feb 17 – Mar 3 | Apr 14 – Apr 28 |
| Brandon | 5a | Feb 6 – Feb 20 | Apr 3 – Apr 17 |
| Brookings | 4b | Feb 11 – Feb 25 | Apr 8 – Apr 22 |
| Harrisburg | 5a | Feb 7 – Feb 21 | Apr 4 – Apr 18 |
| Huron | 4b | Feb 11 – Feb 25 | Apr 8 – Apr 22 |
| Madison | 4b | Feb 10 – Feb 24 | Apr 7 – Apr 21 |
| Mitchell | 5a | Feb 7 – Feb 21 | Apr 4 – Apr 18 |
| Pierre | 4b | Feb 11 – Feb 25 | Apr 8 – Apr 22 |
| Rapid City | 5b | Feb 8 – Feb 22 | Apr 5 – Apr 19 |
| Sioux Falls | 5a | Feb 1 – Feb 15 | Mar 29 – Apr 12 |
| Spearfish | 5b | Feb 17 – Mar 3 | Apr 14 – Apr 28 |
| Sturgis | 5a | Feb 13 – Feb 27 | Apr 10 – Apr 24 |
| Tea | 5a | Feb 1 – Feb 15 | Mar 29 – Apr 12 |
| Vermillion | 5a | Feb 8 – Feb 22 | Apr 5 – Apr 19 |
| Watertown | 4b | Feb 12 – Feb 26 | Apr 9 – Apr 23 |
| Yankton | 5a | Feb 2 – Feb 16 | Mar 30 – Apr 13 |
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 South Dakota, 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.