When to plant in Sun Prairie, WI
USDA Zone 5aEverything below — frost dates, hardiness zone, and what to plant when in Sun Prairie, Wisconsin — is derived from the closest NOAA station with complete climate normals.
Zone 5a means Sun Prairie sees real winter cold, but a good range of perennials survive; the frost dates above govern when annual vegetables go out.
The average first fall frost in Sun Prairie is now 5 days later than in the 1981–2010 normals. See how frost dates are shifting nationwide →
Frost probability
MADISON DANE RGNL AP · 1991–2020The date the last spring and first fall frost occur, by threshold and probability. A 90% date is later in spring — and earlier in fall — than a 10% date; the 50% · 32°F row is what most gardeners plan around. These are Sun Prairie’s own odds, recorded at MADISON DANE RGNL AP.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | May 29 | May 13 | Apr 29 | Sep 17 | Sep 29 | Oct 12 |
| 32°F | May 16 | May 1 | Apr 16 | Sep 26 | Oct 10 | Oct 24 |
| 28°F | May 5 | Apr 20 | Apr 5 | Oct 6 | Oct 22 | Nov 4 |
Download this table as CSV ↓ — every threshold and probability, plus this city’s planting-window dates.
What to plant now
TODAY · JULY 19Full-year planting calendar
Each bar is the exact window to take a planting action in Sun Prairie, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 21 km · complete 32°F normalsWhen stations disagree by more than a few days, that spread is real microclimate variation — elevation, water, urban heat. Judge which station best matches your own yard.
Sun Prairie planting FAQ
When is the last spring frost in Sun Prairie, WI?
On average, the last spring frost in Sun Prairie is around May 1 (50% probability at 32°F, from 1991–2020 NOAA normals). Wait until after this date to set out tender plants like tomatoes and peppers.
When is the first fall frost in Sun Prairie, WI?
The first fall frost in Sun Prairie typically arrives around October 10 (50% probability at 32°F). Harvest or protect frost-sensitive crops before then.
What hardiness zone is Sun Prairie in?
Sun Prairie is in USDA hardiness zone 5a. In zone 5a, winters are cold — pick cold-hardy varieties and protect tender crops.
How long is the growing season in Sun Prairie?
There are roughly 162 frost-free days in Sun Prairie (a moderate growing season), running from the average last frost around May 1 to the first fall frost near October 10.
When should I plant tomatoes in Sun Prairie?
In Sun Prairie, start tomato seeds indoors around March 6–March 20, then transplant seedlings outdoors around May 8 once the danger of frost has passed.
Never miss a window in Sun Prairie
An email when it’s time to start seeds, transplant, and sow — timed to Sun Prairie’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reachFrost dates recorded at MADISON DANE RGNL AP, 10 km from the city center · 1991–2020 NOAA climate normals · zone from the USDA/PRISM 2023 map. How we compute this.
BlissGarden. "When to Plant in Sun Prairie, WI — Frost Dates & Zone 5a." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USW00014837. Retrieved from https://blissgarden.com/wisconsin/sun-prairie.