Sun Prairie, WI planting zone & frost dates
Sun Prairie is in USDA hardiness zone 5a. The last spring frost usually comes around May 1 and the first fall frost around October 10, for a growing season of about 160 days.
Planting calendar for Sun Prairie
Dates are counted from the average last spring frost (May 1) using the typical timing recommended by U.S. extension services. Warm-season crops go out only after the danger of frost has passed and the soil has warmed.
| Crop | When |
|---|---|
| Tomatoes | Start seeds indoors: Mar 6 – Mar 20 Transplant outdoors: May 8 – May 15 |
| Peppers | Start seeds indoors: Feb 20 – Mar 6 Transplant outdoors: May 15 – May 22 |
| Eggplant | Start seeds indoors: Feb 20 – Mar 6 Transplant outdoors: May 15 – May 22 |
| Broccoli | Start seeds indoors: Feb 20 – Mar 6 Transplant outdoors: Apr 3 – Apr 17 |
| Cabbage | Start seeds indoors: Feb 20 – Mar 6 Transplant outdoors: Apr 3 – Apr 17 |
| Onions (sets) | Plant outdoors: Apr 3 – Apr 17 |
| Peas | Sow outdoors: Mar 20 – Apr 3 |
| Spinach | Sow outdoors: Mar 20 – Apr 3 |
| Lettuce | Sow outdoors: Apr 3 – Apr 17 |
| Carrots | Sow outdoors: Apr 3 – Apr 17 |
| Potatoes | Plant outdoors: Apr 3 – Apr 17 |
| Beans | Sow outdoors: May 8 – May 15 |
| Sweet corn | Sow outdoors: May 8 – May 15 |
| Cucumbers | Sow outdoors: May 8 – May 15 |
| Squash & zucchini | Sow outdoors: May 8 – May 15 |
| Basil | Start seeds indoors: Mar 20 – Apr 3 Transplant outdoors: May 8 – May 15 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Aug 15 (8 weeks before the average first fall frost on Oct 10).
Useful for zone 5a gardens
- Seed starting kit with dome — to start seeds indoors before the last frost
- LED grow light for seedlings — stops leggy seedlings
- Frost cloth / plant covers — for late spring and early fall frosts
- Soil thermometer — warm-season crops need soil above 60°F
- Cold frame / mini greenhouse — adds weeks to a short season
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Frost risk in detail
| 90% chance | 50% chance | 10% chance | |
|---|---|---|---|
| Last 32°F frost in spring is after | Apr 16 | May 1 | May 16 |
| First 32°F frost in fall is before | Oct 24 | Oct 10 | Sep 26 |
How to read it: in spring there is a 10% chance of a frost after May 16, so that is a safe date for tender plants. In fall there is a 10% chance of frost before September 26. A hard freeze (28°F) usually ends around April 20.
Hardiness zone by ZIP code in Sun Prairie
- 53590 zone 5a
- 53596 zone 5a
Nearby cities
Questions
What growing zone is Sun Prairie, WI?
Sun Prairie is in USDA Plant Hardiness Zone 5a (average extreme winter low -20°F to -15°F), according to the USDA 2023 map.
When is the last frost in Sun Prairie?
The average last spring frost (32°F) in Sun Prairie is May 1. There is still a 10% chance of frost until May 16.
When can I plant tomatoes in Sun Prairie?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around May 8 – May 15. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Madison Dane Rgnl Ap, WI (USW00014837), 11.7 km (7.3 mi) from the city center, elevation 264 m, based on 29 years of records. Hardiness zone: USDA Plant Hardiness Zone Map 2023 for the ZIP code nearest to the city center. Microclimates (valleys, hills, cities, coasts) can be warmer or colder: check the local forecast before planting. How we calculate the data.