When to Plant Onions in Wisconsin
In Wisconsin, the time to plant onions outside runs from Mar 22 – Apr 5 in Pleasant Prairie to Apr 9 – Apr 23 in Green Bay. In Milwaukee, it's Mar 29 – Apr 12. The average last spring frost differs by about 3 weeks across the state (Apr 19 in Pleasant Prairie, May 7 in Green Bay), 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 Wisconsin by city
| City | Zone | Start indoors | Plant outside |
|---|---|---|---|
| Appleton | 5b | Feb 9 – Feb 23 | Apr 6 – Apr 20 |
| Beloit | 5b | Feb 6 – Feb 20 | Apr 3 – Apr 17 |
| Brookfield | 5b | Feb 5 – Feb 19 | Apr 2 – Apr 16 |
| Caledonia | 6a | Jan 30 – Feb 13 | Mar 27 – Apr 10 |
| De Pere | 5b | Feb 5 – Feb 19 | Apr 2 – Apr 16 |
| Eau Claire | 4b | Jan 30 – Feb 13 | Mar 27 – Apr 10 |
| Fitchburg | 5b | Feb 6 – Feb 20 | Apr 3 – Apr 17 |
| Fond du Lac | 5b | Feb 2 – Feb 16 | Mar 30 – Apr 13 |
| Franklin | 5b | Feb 8 – Feb 22 | Apr 5 – Apr 19 |
| Germantown | 5b | Feb 11 – Feb 25 | Apr 8 – Apr 22 |
| Green Bay | 5b | Feb 12 – Feb 26 | Apr 9 – Apr 23 |
| Greenfield | 5b | Feb 8 – Feb 22 | Apr 5 – Apr 19 |
| Howard | 5b | Feb 12 – Feb 26 | Apr 9 – Apr 23 |
| Janesville | 5b | Feb 1 – Feb 15 | Mar 29 – Apr 12 |
| Kenosha | 5b | Feb 3 – Feb 17 | Mar 31 – Apr 14 |
| La Crosse | 5a | Feb 2 – Feb 16 | Mar 30 – Apr 13 |
| Madison | 5a | Feb 6 – Feb 20 | Apr 3 – Apr 17 |
| Manitowoc | 5b | Feb 5 – Feb 19 | Apr 2 – Apr 16 |
| Menomonee Falls | 5b | Feb 11 – Feb 25 | Apr 8 – Apr 22 |
| Mequon | 5b | Feb 11 – Feb 25 | Apr 8 – Apr 22 |
| Middleton | 5a | Feb 3 – Feb 17 | Mar 31 – Apr 14 |
| Milwaukee | 6a | Feb 1 – Feb 15 | Mar 29 – Apr 12 |
| Mount Pleasant | 5b | Jan 26 – Feb 9 | Mar 23 – Apr 6 |
| Muskego | 5b | Feb 8 – Feb 22 | Apr 5 – Apr 19 |
| Neenah | 5b | Feb 9 – Feb 23 | Apr 6 – Apr 20 |
| New Berlin | 5b | Feb 8 – Feb 22 | Apr 5 – Apr 19 |
| Oak Creek | 6a | Jan 28 – Feb 11 | Mar 25 – Apr 8 |
| Oshkosh | 5b | Jan 30 – Feb 13 | Mar 27 – Apr 10 |
| Pleasant Prairie | 5b | Jan 25 – Feb 8 | Mar 22 – Apr 5 |
| Racine | 6a | Jan 26 – Feb 9 | Mar 23 – Apr 6 |
| Sheboygan | 6a | Jan 31 – Feb 14 | Mar 28 – Apr 11 |
| Stevens Point | 4b | Feb 9 – Feb 23 | Apr 6 – Apr 20 |
| Sun Prairie | 5a | Feb 6 – Feb 20 | Apr 3 – Apr 17 |
| Superior | 5a | Feb 11 – Feb 25 | Apr 8 – Apr 22 |
| Watertown | 5b | Feb 3 – Feb 17 | Mar 31 – Apr 14 |
| Waukesha | 5b | Feb 6 – Feb 20 | Apr 3 – Apr 17 |
| Wausau | 4b | Feb 11 – Feb 25 | Apr 8 – Apr 22 |
| Wauwatosa | 5b | Feb 1 – Feb 15 | Mar 29 – Apr 12 |
| West Allis | 5b | Feb 1 – Feb 15 | Mar 29 – Apr 12 |
| West Bend | 5b | Feb 6 – Feb 20 | Apr 3 – Apr 17 |
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 Wisconsin, or the general guide to when to plant onions.
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