Green Bay, Wisconsin: planting zone & frost dates
Green Bay is in USDA plant hardiness zone 5b, where the average coldest winter night reaches -15 to -10°F (-26.1 to -23.3°C). The typical last spring frost is around May 13 and the first fall frost around Oct 2.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | May 22 | Sep 23 |
| Typical planning date (30% risk) | May 13 | Oct 2 |
| Median (50%) | May 7 | Oct 9 |
How to read this: after the spring "10% risk" date, a 32°F frost happens in only about 1 year in 10. In fall, the "10% risk" date is the early end — a frost before it happens about 1 year in 10.
Frost data comes from NOAA station GREEN BAY BOTANICAL, WI (USC00473271), 5.5 mi (8.9 km) from the city center and 112 ft higher than the city center (+34 m). Record used for the 1991–2020 normals: 19 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Green Bay
All 7 ZIP codes covering Green Bay are in zone 5b.
Vegetable planting calendar for Green Bay
Dates are counted from the 30%-risk frost dates above (last frost May 13, first frost Oct 2). Shift a week later in cold spots or low-lying ground.
| Crop | Start indoors | Transplant / plant out | Direct sow | Fall crop sow/plant |
|---|---|---|---|---|
| Tomato | Mar 18 – Apr 1 | May 20 – Jun 3 | — | — |
| Pepper | Mar 4 – Mar 18 | May 27 – Jun 10 | — | — |
| Lettuce | Apr 1 – Apr 15 | Apr 29 – May 20 | Apr 15 – May 27 | Jul 24 – Aug 21 |
| Green Beans | — | — | May 20 – Jun 24 | Jul 10 – Jul 24 |
| Sweet Corn | — | — | May 20 – Jun 17 | — |
| Zucchini & Summer Squash | Apr 15 – Apr 22 | May 20 – Jun 3 | May 20 – Jun 10 | Jul 10 – Jul 24 |
| Cucumber | Apr 15 – Apr 22 | May 27 – Jun 3 | May 20 – Jun 10 | Jul 10 – Jul 24 |
| Carrot | — | — | Apr 22 – May 27 | Jul 10 – Jul 24 |
| Onion | Feb 18 – Mar 4 | Apr 15 – Apr 29 | — | — |
| Potato | — | Apr 15 – May 6 | — | — |
| Basil | Apr 1 – Apr 15 | May 27 – Jun 10 | May 27 – Jun 17 | — |
| Spinach | — | — | Apr 1 – Apr 29 | Aug 7 – Sep 4 |
| Kale | Mar 18 – Apr 1 | Apr 15 – May 6 | Apr 15 – May 6 | Jul 24 – Aug 21 |
| Broccoli | Mar 18 – Apr 1 | Apr 29 – May 20 | — | Jul 10 – Jul 24 |
| Peas | — | — | Apr 1 – Apr 22 | Jul 24 – Aug 7 |
| Eggplant | Mar 4 – Mar 18 | May 27 – Jun 10 | — | — |
| Cabbage | Mar 18 – Apr 1 | Apr 15 – Apr 29 | — | Jul 10 – Jul 24 |
| Radish | — | — | Apr 8 – May 27 | Aug 21 – Sep 18 |
| Strawberry | — | Apr 15 – May 6 | — | — |
| Beets | — | — | Apr 22 – Jun 3 | Jul 24 – Aug 7 |
Nearby cities in Wisconsin
- Milwaukee — zone 6a, last frost May 2, first frost Oct 12
- Racine — zone 6a, last frost Apr 27, first frost Oct 18
- Kenosha — zone 5b, last frost May 3, first frost Oct 14
- Madison — zone 5b, last frost May 7, first frost Oct 3
More: all Wisconsin cities · other zone 5b cities: Madison, WI, Des Moines, IA, Aurora, IL, Fort Collins, CO, Naperville, IL, Rockford, IL, Elgin, IL, Greeley, CO
Green Bay gardening questions
When is the last frost in Green Bay, WI?
Plan around May 13. At NOAA's Green Bay Botanical, WI station, 5.5 mi from the city center, there is a 30% chance of a 32°F frost after that date. Half of springs have their last frost by May 7, and after May 22 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Apr 27. The last frost is fairly predictable here: only 28 days separate the 90% and 10% dates (median for cities on this site: 36 days).
When should I plant tomatoes in Green Bay, WI?
Start seeds indoors Mar 18 – Apr 1 and set transplants outside May 20 – Jun 3, once nights stay above 50°F and the soil is near 60°F. That leaves 142 days between the 30% frost dates, enough for most varieties including 80–85-day slicers. More: tomato planting dates by zone.
How long is the growing season in Green Bay?
About 154 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 134 days, and in 1 year in 10 it runs 176 days or more. In fall there is a 10% chance of frost by Sep 23 and a 30% chance by Oct 2. That is the shortest of the 5 Wisconsin cities on this site.
When should I plant a fall garden in Green Bay?
Count back from the first fall frost (Oct 2): transplant broccoli Jul 10 – Jul 24; sow kale Jul 24 – Aug 21; sow lettuce Jul 24 – Aug 21; sow radishes Aug 21 – Sep 18. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Oct 25. How the math works: succession and fall planting.
Did Green Bay's hardiness zone change on the 2023 map?
Yes. Most of Green Bay was zone 5a on the 2012 map and is zone 5b on the 2023 map — half a zone warmer, like about 56% of U.S. ZIP codes. The shift comes from a newer 1991–2020 averaging period plus more weather stations and better mapping; it does not mean last frost comes earlier. Why the 2023 map is warmer.
How does Green Bay compare with Milwaukee, WI?
Green Bay is zone 5b and Milwaukee is zone 6a. The typical last spring frost in Green Bay (May 13) comes about 11 days later than in Milwaukee, WI (May 2), 101 miles away, and the first fall frost is Oct 2 versus Oct 12. The two cities use different NOAA stations.