Oconomowoc, WI planting zone & frost dates
Oconomowoc is in USDA hardiness zone 5b. The last spring frost usually comes around April 30 and the first fall frost around October 12, for a growing season of about 164 days.
Planting calendar for Oconomowoc
Dates are counted from the average last spring frost (April 30) 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 5 – Mar 19 Transplant outdoors: May 7 – May 14 |
| Peppers | Start seeds indoors: Feb 19 – Mar 5 Transplant outdoors: May 14 – May 21 |
| Eggplant | Start seeds indoors: Feb 19 – Mar 5 Transplant outdoors: May 14 – May 21 |
| Broccoli | Start seeds indoors: Feb 19 – Mar 5 Transplant outdoors: Apr 2 – Apr 16 |
| Cabbage | Start seeds indoors: Feb 19 – Mar 5 Transplant outdoors: Apr 2 – Apr 16 |
| Onions (sets) | Plant outdoors: Apr 2 – Apr 16 |
| Peas | Sow outdoors: Mar 19 – Apr 2 |
| Spinach | Sow outdoors: Mar 19 – Apr 2 |
| Lettuce | Sow outdoors: Apr 2 – Apr 16 |
| Carrots | Sow outdoors: Apr 2 – Apr 16 |
| Potatoes | Plant outdoors: Apr 2 – Apr 16 |
| Beans | Sow outdoors: May 7 – May 14 |
| Sweet corn | Sow outdoors: May 7 – May 14 |
| Cucumbers | Sow outdoors: May 7 – May 14 |
| Squash & zucchini | Sow outdoors: May 7 – May 14 |
| Basil | Start seeds indoors: Mar 19 – Apr 2 Transplant outdoors: May 7 – May 14 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Aug 17 (8 weeks before the average first fall frost on Oct 12).
Useful for zone 5b 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 | Apr 30 | May 17 |
| First 32°F frost in fall is before | Oct 27 | Oct 12 | Sep 29 |
How to read it: in spring there is a 10% chance of a frost after May 17, so that is a safe date for tender plants. In fall there is a 10% chance of frost before September 29. A hard freeze (28°F) usually ends around April 19.
Hardiness zone by ZIP code in Oconomowoc
- 53066 zone 5b
Nearby cities
- Hartford zone 5a, last frost May 8
- Watertown zone 5b, last frost Apr 28
- Sussex zone 5b, last frost Apr 30
- Waukesha zone 5b, last frost May 1
- Richfield zone 5b, last frost Apr 30
- Whitewater zone 5b, last frost May 2
- Fort Atkinson zone 5b, last frost Apr 28
- Menomonee Falls zone 5b, last frost May 6
Questions
What growing zone is Oconomowoc, WI?
Oconomowoc is in USDA Plant Hardiness Zone 5b (average extreme winter low -15°F to -10°F), according to the USDA 2023 map.
When is the last frost in Oconomowoc?
The average last spring frost (32°F) in Oconomowoc is April 30. There is still a 10% chance of frost until May 17.
When can I plant tomatoes in Oconomowoc?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around May 7 – May 14. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Oconomowoc Wwtp, WI (USC00476200), 1.3 km (0.8 mi) from the city center, elevation 262 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.