Ann Arbor, Michigan: planting zone & frost dates
Ann Arbor is in USDA plant hardiness zone 6a, where the average coldest winter night reaches -10 to -5°F (-23.3 to -20.6°C). The typical last spring frost is around May 11 and the first fall frost around Oct 4.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | May 20 | Sep 28 |
| Typical planning date (30% risk) | May 11 | Oct 4 |
| Median (50%) | May 5 | Oct 10 |
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 ANN ARBOR SE, MI (USC00200228), 3.0 mi (4.9 km) from the city center and 56 ft lower than the city center (-17 m). Record used for the 1991–2020 normals: 17 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Ann Arbor
All 5 ZIP codes covering Ann Arbor are in zone 6a.
Vegetable planting calendar for Ann Arbor
Dates are counted from the 30%-risk frost dates above (last frost May 11, first frost Oct 4). 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 16 – Mar 30 | May 18 – Jun 1 | — | — |
| Pepper | Mar 2 – Mar 16 | May 25 – Jun 8 | — | — |
| Lettuce | Mar 30 – Apr 13 | Apr 27 – May 18 | Apr 13 – May 25 | Jul 26 – Aug 23 |
| Green Beans | — | — | May 18 – Jun 22 | Jul 12 – Jul 26 |
| Sweet Corn | — | — | May 18 – Jun 15 | — |
| Zucchini & Summer Squash | Apr 13 – Apr 20 | May 18 – Jun 1 | May 18 – Jun 8 | Jul 12 – Jul 26 |
| Cucumber | Apr 13 – Apr 20 | May 25 – Jun 1 | May 18 – Jun 8 | Jul 12 – Jul 26 |
| Carrot | — | — | Apr 20 – May 25 | Jul 12 – Jul 26 |
| Onion | Feb 16 – Mar 2 | Apr 13 – Apr 27 | — | — |
| Potato | — | Apr 13 – May 4 | — | — |
| Basil | Mar 30 – Apr 13 | May 25 – Jun 8 | May 25 – Jun 15 | — |
| Spinach | — | — | Mar 30 – Apr 27 | Aug 9 – Sep 6 |
| Kale | Mar 16 – Mar 30 | Apr 13 – May 4 | Apr 13 – May 4 | Jul 26 – Aug 23 |
| Broccoli | Mar 16 – Mar 30 | Apr 27 – May 18 | — | Jul 12 – Jul 26 |
| Peas | — | — | Mar 30 – Apr 20 | Jul 26 – Aug 9 |
| Eggplant | Mar 2 – Mar 16 | May 25 – Jun 8 | — | — |
| Cabbage | Mar 16 – Mar 30 | Apr 13 – Apr 27 | — | Jul 12 – Jul 26 |
| Radish | — | — | Apr 6 – May 25 | Aug 23 – Sep 20 |
| Strawberry | — | Apr 13 – May 4 | — | — |
| Beets | — | — | Apr 20 – Jun 1 | Jul 26 – Aug 9 |
Nearby cities in Michigan
- Westland — zone 6b, last frost Apr 28, first frost Oct 22
- Livonia — zone 6b, last frost May 8, first frost Oct 10
- Farmington Hills — zone 6a, last frost May 8, first frost Oct 10
- Southfield — zone 6b, last frost May 8, first frost Oct 10
- Dearborn — zone 6b, last frost May 8, first frost Oct 9
- Detroit — zone 6b, last frost May 2, first frost Oct 20
More: all Michigan cities · other zone 6a cities: Chicago, IL, Denver, CO, Milwaukee, WI, Colorado Springs, CO, Omaha, NE, Aurora, CO, Lincoln, NE, Fort Wayne, IN
Ann Arbor gardening questions
When is the last frost in Ann Arbor, MI?
Plan around May 11. At NOAA's Ann Arbor SE, MI station, 3.0 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 5, and after May 20 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Apr 24. The 90% and 10% dates are 29 days apart, close to the 36-day median for cities on this site.
When should I plant tomatoes in Ann Arbor, MI?
Start seeds indoors Mar 16 – Mar 30 and set transplants outside May 18 – Jun 1, once nights stay above 50°F and the soil is near 60°F. That leaves 146 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 Ann Arbor?
About 157 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 138 days, and in 1 year in 10 it runs 176 days or more. In fall there is a 10% chance of frost by Sep 28 and a 30% chance by Oct 4. That is the shortest of the 15 Michigan cities on this site.
When should I plant a fall garden in Ann Arbor?
Count back from the first fall frost (Oct 4): transplant broccoli Jul 12 – Jul 26; sow kale Jul 26 – Aug 23; sow lettuce Jul 26 – Aug 23; sow radishes Aug 23 – Sep 20. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Oct 23. How the math works: succession and fall planting.
Did Ann Arbor's hardiness zone change on the 2023 map?
No. Going by the zone that covers most of the city's land, Ann Arbor is zone 6a on both the 2012 and the 2023 USDA maps (PRISM/OSU ZIP listings). About 42% of U.S. ZIP codes kept their half-zone in 2023. Why the 2023 map is warmer.
How does Ann Arbor compare with Westland, MI?
Ann Arbor is zone 6a and Westland is zone 6b. The typical last spring frost in Ann Arbor (May 11) comes about 13 days later than in Westland, MI (Apr 28), 18 miles away, and the first fall frost is Oct 4 versus Oct 22. Ann Arbor sits about 234 ft higher, which explains part of the gap. The two cities use different NOAA stations.