Last spring frost
May 8
Frost Dates for Ann Arbor, MI
First fall frost
Oct 4
Growing season
147 days
Hardiness zone
6a
In an average year around Ann Arbor, MI, the last spring frost (32°F) is about May 8 and the first fall frost is about Oct 4, giving roughly a 147-day growing season. To be safe most years, wait until Apr 23 before setting out tender plants.
Last spring frost
Dates the last frost of spring typically ends. Plant tender crops after the risk has passed for your comfort level.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Light (36°F) | Jun 10 | May 24 | May 5 |
| Freeze (32°F) | May 26 | May 8 | Apr 23 |
| Hard (28°F) | May 15 | Apr 27 | Apr 12 |
| Severe (24°F) | May 4 | Apr 16 | Apr 1 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 10 | Jun 3 | May 30 | May 27 | May 24 | May 20 | May 15 | May 10 | May 5 |
| 32°F | May 26 | May 22 | May 16 | May 12 | May 8 | May 5 | May 2 | Apr 28 | Apr 23 |
| 28°F | May 15 | May 10 | May 5 | May 1 | Apr 27 | Apr 24 | Apr 20 | Apr 17 | Apr 12 |
| 24°F | May 4 | Apr 27 | Apr 22 | Apr 19 | Apr 16 | Apr 12 | Apr 8 | Apr 5 | Apr 1 |
| 20°F | Apr 19 | Apr 12 | Apr 7 | Apr 4 | Apr 2 | Mar 30 | Mar 27 | Mar 22 | Mar 16 |
| 16°F | Apr 4 | Mar 31 | Mar 28 | Mar 25 | Mar 21 | Mar 18 | Mar 15 | Mar 11 | Mar 5 |
First fall frost
Dates the first frost of fall typically arrives. Count back by a crop's days-to-maturity to know your planting cutoff.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Light (36°F) | Sep 10 | Sep 24 | Oct 6 |
| Freeze (32°F) | Sep 20 | Oct 4 | Oct 17 |
| Hard (28°F) | Sep 30 | Oct 16 | Oct 31 |
| Severe (24°F) | Oct 15 | Oct 30 | Nov 13 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 10 | Sep 15 | Sep 18 | Sep 21 | Sep 24 | Sep 26 | Sep 29 | Oct 2 | Oct 6 |
| 32°F | Sep 20 | Sep 24 | Sep 28 | Oct 1 | Oct 4 | Oct 6 | Oct 9 | Oct 12 | Oct 17 |
| 28°F | Sep 30 | Oct 5 | Oct 8 | Oct 12 | Oct 16 | Oct 19 | Oct 22 | Oct 26 | Oct 31 |
| 24°F | Oct 15 | Oct 19 | Oct 23 | Oct 26 | Oct 30 | Nov 1 | Nov 4 | Nov 7 | Nov 13 |
| 20°F | Oct 25 | Nov 1 | Nov 4 | Nov 7 | Nov 10 | Nov 13 | Nov 17 | Nov 22 | Nov 27 |
| 16°F | Nov 6 | Nov 10 | Nov 14 | Nov 18 | Nov 22 | Nov 26 | Nov 30 | Dec 4 | Dec 10 |
Growing season is measured at 32°F with about 50% probability. Hardiness zone from the 2023 USDA map; frost normals from NOAA 1991-2020.
Where this data comes from
@endif These dates are computed from the nearest official weather station with long-term records: Ann Arbor Muni Ap, Mi, about 5.9 miles away@if(!empty($station['elevation_ft'])), at 839 ft elevation. The further the station and the greater the elevation difference from your yard, the more your local frost timing can vary.
How we calculate these dates
Frost and freeze dates come from the NOAA 1991–2020 U.S. Climate Normals, the National Oceanic and Atmospheric Administration's 30-year averages for each weather station. A date shown at the 50% level is the median: in half of years the frost falls on or before it. The 10% and 90% columns show the early and late ends of the range, so you can plant on the odds you're comfortable with. These are long-term averages, not a forecast for this year - always check your local outlook before planting.
Source: NOAA National Centers for Environmental Information, 1991–2020 Climate Normals (public domain). Harman is not affiliated with or endorsed by NOAA.
Frequently asked questions
When is the last frost in Ann Arbor, MI?
On average, the last spring frost (32°F) around Ann Arbor, MI is about May 8. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 23.
When is the first frost in the fall?
The first fall frost around Ann Arbor, MI typically arrives about Oct 4. Count back by a crop's days to maturity to find the latest date you can plant it.
When can I plant tomatoes and other tender crops?
Tender crops like tomatoes, peppers and basil are damaged by frost, so wait until the last spring frost has passed - around May 8 on average, or Apr 23 to be safe most years.
How long is the growing season here?
The frost-free growing season (between the last spring and first fall 32°F frost) is about 147 days in a typical year.
Are these dates a forecast for this year?
No. They are 30-year averages from the NOAA 1991–2020 Climate Normals, not a prediction for the current year. Use them for planning and always check your local weather forecast before planting or protecting crops.
Local weather for 48103 Planting calendar → Michigan frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026