Hartford, WI planting zone & frost dates
Hartford is in USDA hardiness zone 5a. The last spring frost usually comes around May 8 and the first fall frost around October 3, for a growing season of about 148 days.
Planting calendar for Hartford
Dates are counted from the average last spring frost (May 8) 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 13 – Mar 27 Transplant outdoors: May 15 – May 22 |
| Peppers | Start seeds indoors: Feb 27 – Mar 13 Transplant outdoors: May 22 – May 29 |
| Eggplant | Start seeds indoors: Feb 27 – Mar 13 Transplant outdoors: May 22 – May 29 |
| Broccoli | Start seeds indoors: Feb 27 – Mar 13 Transplant outdoors: Apr 10 – Apr 24 |
| Cabbage | Start seeds indoors: Feb 27 – Mar 13 Transplant outdoors: Apr 10 – Apr 24 |
| Onions (sets) | Plant outdoors: Apr 10 – Apr 24 |
| Peas | Sow outdoors: Mar 27 – Apr 10 |
| Spinach | Sow outdoors: Mar 27 – Apr 10 |
| Lettuce | Sow outdoors: Apr 10 – Apr 24 |
| Carrots | Sow outdoors: Apr 10 – Apr 24 |
| Potatoes | Plant outdoors: Apr 10 – Apr 24 |
| Beans | Sow outdoors: May 15 – May 22 |
| Sweet corn | Sow outdoors: May 15 – May 22 |
| Cucumbers | Sow outdoors: May 15 – May 22 |
| Squash & zucchini | Sow outdoors: May 15 – May 22 |
| Basil | Start seeds indoors: Mar 27 – Apr 10 Transplant outdoors: May 15 – May 22 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Aug 8 (8 weeks before the average first fall frost on Oct 3).
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 24 | May 8 | May 24 |
| First 32°F frost in fall is before | Oct 16 | Oct 3 | Sep 20 |
How to read it: in spring there is a 10% chance of a frost after May 24, so that is a safe date for tender plants. In fall there is a 10% chance of frost before September 20. A hard freeze (28°F) usually ends around April 27.
Hardiness zone by ZIP code in Hartford
- 53027 zone 5a
Nearby cities
- Richfield zone 5b, last frost Apr 30
- West Bend zone 5b, last frost May 1
- Oconomowoc zone 5b, last frost Apr 30
- Sussex zone 5b, last frost Apr 30
- Germantown zone 5b, last frost May 6
- Menomonee Falls zone 5b, last frost May 6
- Waukesha zone 5b, last frost May 1
- Mequon zone 5b, last frost May 6
Questions
What growing zone is Hartford, WI?
Hartford 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 Hartford?
The average last spring frost (32°F) in Hartford is May 8. There is still a 10% chance of frost until May 24.
When can I plant tomatoes in Hartford?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around May 15 – May 22. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Hartford Wwtp, WI (USC00473453), 3.1 km (1.9 mi) from the city center, elevation 293 m, based on 27 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.