Frost dates for Ann Arbor, Michigan
In Ann Arbor, half of springs have had their last frost by May 8 (and 1 spring in 10 still has one after May 26), and half of falls have had their first frost by October 4, leaving about 147 frost-free days in a typical year. Here is how sure those dates are, what they mean for planting, and where they come from.
Frost dates for
Ann Arbor, Michigan
Last spring frost
May 8
Half of springs have their last frost by this date. For a safer bet, wait until May 26: only 1 spring in 10 has a frost after that.
First fall frost
October 4
Half of falls have their first frost by this date. In 1 fall in 10 it comes by September 20.
Growing season
147 days
Frost-free days in a typical year. 9 years in 10 get at least 124.
Hardiness zone
6a
2023 USDA map: the coldest night of winter averages −10°F to −5°F. It was 6a on the 2012 map too. All 5 ZIP codes within about 6 miles of the city's center are in zone 6a.
Stations near you disagree. NOAA's Ann Arbor Municipal Airport (4 miles away, at 840 feet above sea level), the one we used, gives a typical last frost of May 8 and a typical first frost of October 4. NOAA's Detroit Willow Run Airport (10 miles away, at 780 feet above sea level) gives a typical last frost of April 24 and a typical first frost of October 24. So the typical last frost could fall anywhere from April 24 to May 8 and the typical first frost from October 4 to 24, depending on whether your garden is more like one or the other. Local terrain matters: hillsides, valley floors, water and city heat can change frost dates a lot over a few miles. Treat the dates here as a starting point, and compare with a nearby gardener or your county extension office.
Print a year planner for Ann Arbor
Frost risk through the year
How sure are these dates?
A frost date is a probability, not a promise. NOAA worked out, from 30 years of nightly lows, how often the last spring frost and the first fall frost fall on each date. The middle column is the typical year. The outer columns are the early and late years that come about once a decade.
| Early year 1 in 10 | Typical year 1 in 2 | Late year 1 in 10 | |
|---|---|---|---|
| Last frost in spring | April 23 | May 8 | May 26 |
| First frost in fall | September 20 | October 4 | October 17 |
The frost-free season between them runs 147 days in a typical year. In 1 year in 10 it is 167 days or longer, and in 1 year in 10 it is 124 days or shorter.
- Hard freeze (28°F): typically last on April 27 and first on October 16. It is a harder freeze than the 32°F frost line, cold enough to damage many garden plants; how hardy a crop is decides whether it comes through. (The National Weather Service's own hard-freeze threshold varies from office to office.)
- Frost possible (36°F at the station): typically last on May 24 and first on September 24. On clear, still nights the ground can be several degrees colder than the thermometer, so frost can form on plants when the official reading is in the mid-30s.
In 8 springs out of 10, the last frost in Ann Arbor comes between April 23 and May 26, a window of 33 days. That is about average for NOAA's stations (the typical window is 31 days).
Among Michigan's 211 NOAA stations with a frost every year, 49 percent have their typical last frost later than Ann Arbor does.
Planting calendar for Ann Arbor
These dates count from the typical last and first frosts, using the planting rules published by Colorado State University Extension (spring), Virginia Cooperative Extension (fall crops) and University of Minnesota Extension (garlic, where winters are hard). Weather in any one year can run early or late, so check the forecast before you plant tender crops.
Your season is too short for a separate fall planting of cabbage: sown late enough to be a fall crop, it wouldn't be ready before the typical first frost. Your spring planting is your harvest.
| When | What to do | Why then |
|---|---|---|
| February | ||
| February 20 to March 20 | Broccoli and cabbage Start seeds indoors | 5 to 7 weeks before planting them out |
| March | ||
| March 6 to April 3 | Cauliflower Start seeds indoors | 5 to 7 weeks before planting out |
| March 20 to April 10 | Eggplant Start seeds indoors | 6 to 9 weeks before planting out |
| March 27 to April 10 | Peppers Start seeds indoors | 6 to 8 weeks before planting out |
| April | ||
| April 3 to 17 | Tomatoes Start seeds indoors | 5 to 7 weeks before planting out |
| April 10 to 24 | Peas, spinach, lettuce, radishes, onion sets, turnips Sow outdoors, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April 10 to 24 | Broccoli and cabbage Plant out, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April 24 to May 8 | Beets, carrots, potatoes, Swiss chard Plant outdoors, as early as | semi-hardy crops: up to 2 weeks before the typical last frost |
| April 24 to May 8 | Cauliflower Plant out, as early as | semi-hardy: up to 2 weeks before the typical last frost |
| May | ||
| May 8 | Snap beans, sweet corn, cucumbers, summer squash Sow outdoors around | tender crops: around the typical last frost date |
| May 22 | Tomatoes, peppers, eggplant Plant out from | very tender: 2 weeks or more after the typical last frost |
| May 22 | Melons, winter squash, pumpkins, lima beans Sow outdoors from | very tender: 2 weeks or more after the typical last frost |
| May 29 to June 12 | Broccoli for fall Start seeds | set the plants out by July 17 |
| July | ||
| July 8 | Snap beans for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| July 12 | Carrots for fall Last date to sow | 70 days to harvest, plus 2 weeks for slower fall growth |
| July 13 | Cucumbers for fall Last date to sow | 55 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| July 17 | Peas for fall Last date to sow | 65 days to harvest, plus 2 weeks for slower fall growth |
| July 18 | Summer squash for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| July 22 | Leaf lettuce and beets for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth |
| August | ||
| August 1 | Turnips and kohlrabi for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth |
| August 11 | Spinach for fall Last date to sow | 40 days to harvest, plus 2 weeks for slower fall growth |
| August 21 | Radishes for fall Last date to sow | 30 days to harvest, plus 2 weeks for slower fall growth |
| September | ||
| September 20 | Tomatoes, peppers, squash, melons, cucumbers Watch the forecast from | in 1 fall in 10 the first frost comes by this date; pick tender crops before a frost |
| October | ||
| October 23 to 30 | Garlic Plant cloves | one or two weeks after the typical first hard freeze (28°F), our reading of the first killing frost |
Want more insurance? Shift every spring date 18 days later. That plans around May 26, the date after which only 1 spring in 10 has a frost.
For spring bulbs such as tulips and daffodils, plant once the soil has cooled to about 50 to 55°F and keep going until a couple of weeks before the ground freezes. Our guide to fall planting explains how to tell.
Where these numbers come from
These dates come from NOAA's weather station Ann Arbor Municipal Airport (station USW00094889), 4 miles from the center of Ann Arbor. It sits at about the same elevation, 840 feet above sea level. NOAA rates this station's record as representative: at least 10 of the 30 years, with the gaps filled from nearby stations.
Our ZIP code lookup matches these 2 ZIP codes to the same station, so they get the same dates: 48103, 48108. Hardiness zones are worked out separately for each ZIP code.
Nearby places
- Detroit, Michigan: last frost around April 21, first frost around October 31 (35 miles away)
- Sterling Heights, Michigan: last frost around April 30, first frost around October 24 (40 miles away)
- Toledo, Ohio: last frost around April 20, first frost around October 27 (45 miles away)
See frost dates across Michigan, or look up your own ZIP code for the station nearest you. Want the background? Read what a last frost date really means.