GardenFacts

All states › Michigan › Ann Arbor

Frost dates and planting calendar for Ann Arbor, Michigan

Updated October 30, 2026. Based on USDA, NOAA and Colorado State University Extension data. Published by Humblebee.

USDA hardiness zone
6a[1]
Median last spring frost
May 3[2]
Median first fall frost
Oct 13[3]
Growing season, median
160 days[4]

Ann Arbor, Michigan is in USDA hardiness zone 6a[1]. The median last spring frost is May 3, based on NOAA records from 1991 to 2020[2].

Frost dates

JanFebMarAprMayJunJulAugSepOctNovDecLast spring frost: 9 in 10 years after Apr 20, half of years May 3, 1 in 10 years after May 20Last frostmedian May 3First fall frost: 9 in 10 years before Oct 27, half of years Oct 13, 1 in 10 years before Sep 29First frostmedian Oct 13Frost riskHardyHardy vegetables: plant Apr 5 to Apr 19Apr 5 to Apr 19Semi-hardySemi-hardy vegetables: plant Apr 19 to May 3Apr 19 to May 3TenderTender vegetables: plant around May 3around May 3Very tenderVery tender vegetables: plant from May 17from May 17
Shaded: the span between the dates frost passes in 9 of 10 years and 1 of 10 years[2][3]. Green: planting windows from the CSU rules applied to the median last frost (GardenFacts calculation)[6]. Exact dates are in the tables below.

These frost dates come from the NOAA weather station Ann Arbor U Of Mich, using 29 years of records from 1991 to 2020[5]. In half of years the last spring frost comes after May 3, and in 1 of 10 years it comes after May 20[2]. In half of years the first fall frost comes before October 13, and in 1 of 10 years it comes before September 29[3]. These are chances from past years, not a forecast, so any year can be earlier or later[2][3].

Frost Likely (9 in 10 years) Even odds (5 in 10) Unlikely (1 in 10)
Last spring frost (32°F)[2] after April 20 after May 3 after May 20
First fall frost (32°F)[3] before September 29 before October 13 before October 27
  • Hard freeze (28°F): median last spring date April 23, median first fall date October 26[7].
  • Frost-free growing season: at least 138 days in 9 of 10 years, 160 days in half of years and 179 days in 1 of 10 years[4].
  • The low reached 32°F or colder in 100% of years and 28°F or colder in 100% of years[8].
  • Weather station: Ann Arbor U Of Mich (USC00200230), 3.7 miles from the city center, 813 feet, 29 years of 1991 to 2020 records[5].

When to plant vegetables

Colorado State University Extension wrote its planting guide for Colorado, so treat these dates as a starting point[6]. Hardy vegetables such as lettuce, peas and spinach can go in as early as 2 to 4 weeks before the median last frost, which works out to April 5 to April 19[6]. Semi-hardy vegetables such as carrots and potatoes can go in as early as 2 weeks before the median last frost, which is April 19[9]. Tender vegetables such as snap beans and sweet corn can be sown from seed around May 3[10]. Very tender vegetables such as tomatoes and peppers typically wait 2 or more weeks after the median last frost, so the earliest start is May 17[11].

  • Hardy (broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips): as early as 2 to 4 weeks before the median last frost (May 3) is April 5 to April 19[6]
  • Semi-hardy (beets, carrots, cauliflower, parsnips, potatoes, Swiss chard): as early as 2 weeks before the median last frost (May 3) is April 19, up to the median date itself[9]
  • Tender (snap beans, sweet corn, cucumbers, summer squash): from seed around the median last frost date, May 3[10]
  • Very tender (cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon): the earliest start, two weeks after the median last frost (May 3), is May 17[11]
Vegetable (CSU group) Plant from First harvest around
Broccoli (hardy)[12] Apr 5 Jun 9 (from transplants)
Cabbage (hardy)[12] Apr 5 Jun 29 (from transplants)
Kohlrabi (hardy)[12] Apr 5 May 25
Lettuce (hardy)[12] Apr 5 Jun 4
Onions (hardy)[12] Apr 5 Jul 24
Peas (hardy)[12] Apr 5 Jun 9
Radishes (hardy)[12] Apr 5 May 5
Spinach (hardy)[12] Apr 5 May 15
Turnips (hardy)[12] Apr 5 May 25
Beets (semi-hardy)[12] Apr 19 Jun 18
Carrots (semi-hardy)[12] Apr 19 Jun 28
Cauliflower (semi-hardy)[12] Apr 19 not listed
Parsnips (semi-hardy)[12] Apr 19 Jun 28
Potatoes (semi-hardy)[12] Apr 19 Aug 22
Swiss chard (semi-hardy)[12] Apr 19 Jun 18
Snap beans (tender)[12] May 3 Jul 2
Sweet corn (tender)[12] May 3 Jul 2
Cucumbers (tender)[12] May 3 Jun 27
Summer squash (tender)[12] May 3 Jun 22
Cantaloupe (very tender)[12] May 17 Aug 10
Eggplant (very tender)[12] May 17 Jul 16 (from transplants)
Peppers (very tender)[12] May 17 Jul 26 (from transplants)
Tomatoes (very tender)[12] May 17 Jul 21 (from transplants)
Winter squash (very tender)[12] May 17 Aug 25
Watermelon (very tender)[12] May 17 Aug 10
Spacing, depth and soil temperature (CSU Extension)
Vegetable Min. soil temp Depth Spacing Days to harvest
Broccoli[13] 40°F 1/2 in 18 in 65
Cabbage[13] 40°F 1/2 in 18 in 85
Kohlrabi[13] 40°F 1/2 in 7-9 in 50
Lettuce[13] 35°F 1/4 in 7-9 in 60
Onions[13] 35°F 1/4 in (seed), 1-2 in (sets) 4-6 in 110
Peas[13] 40°F 1 in 4-6 in 65
Radishes[13] 40°F 1/2 in 2-3 in 30
Spinach[13] 40°F 1/2 in 4-6 in 40
Turnips[13] 40°F 1/2 in 4-6 in 50
Beets[13] 40°F 3/4-1 in 4-6 in 60
Carrots[13] 40°F 1/4 in 2-3 in 70
Cauliflower[13] 40°F 1/2 in 18 in –
Parsnips[13] 35°F 1/2 in 5-6 in 70
Potatoes[13] 45°F – – 125
Swiss chard[13] 40°F 1 in 7-9 in 60
Snap beans[13] 55°F 1-1 1/2 in 6 in 60
Sweet corn[13] 50°F 1-1 1/2 in 12 x 30 in or 9 x 36 in 60-90
Cucumbers[13] 60°F 1 in 6 in trellised, 24-36 in untrellised 55
Summer squash[13] 60°F 1-1 1/2 in 36-48 in 50
Cantaloupe[13] 60°F 1-1 1/2 in 36-48 in 85
Eggplant[13] 60°F 1/4 in 18-24 in 60
Peppers[13] 60°F 1/4 in 15-18 in 70
Tomatoes[13] 50°F 1/4 in 24 in trellised 65
Winter squash[13] 60°F 1-1 1/2 in 36-48 in 100
Watermelon[13] 60°F 1-1 1/2 in 36-48 in 85

Hardiness zone

The 2023 USDA map puts the center of Ann Arbor in zone 6a[1]. The zone is based on the average coldest night of the winter, not on summer heat or frost dates[14]. All of the city's land area lies in ZIP code areas rated zone 6a, so the city does not span more than one zone[15].

Zone 6a: average annual extreme minimum temperature -10°F to -5°F (1991 to 2020)[1]. Modeled value at the city center: -7.2°F[1].

Share of the city's land area by ZIP code zone: zone 6a 100%[15].

All towns in zone 6a and what zone 6a means

Zone by ZIP code
ZIP code Zone Coldest night range
48103[15] 6a -10 to -5°F
48105[15] 6a -10 to -5°F
48104[15] 6a -10 to -5°F
48108[15] 6a -10 to -5°F
48109[15] 6a -10 to -5°F

Questions people ask

What growing zone is Ann Arbor?
The 2023 USDA map puts the center of Ann Arbor in zone 6a[1].
When is the last frost in Ann Arbor?
The median last spring frost is May 3[2]. In 1 of 10 years it comes after May 20[2].
When to plant tomatoes in Ann Arbor?
CSU Extension says tomatoes typically go in 2 or more weeks after the average last frost, which gives an earliest start of May 17[11].
When is the first frost in Ann Arbor?
The median first fall frost is October 13[3]. In 1 of 10 years it comes before September 29[3].
How long is the growing season in Ann Arbor?
The growing season is at least 160 days in half of years[4]. It is at least 138 days in 9 of 10 years[4].

Facts and sources

  1. The 2023 USDA Plant Hardiness Zone Map puts the center of Ann Arbor, Michigan in zone 6a. Zone 6a means an average annual extreme minimum temperature of -10°F to -5°F over 1991 to 2020. The map's modeled value at the city center is minus 7.2°F. USDA zone map 2023 (PRISM, OSU)
  2. Last spring frost (32°F) at this station: in 9 of 10 years the last frost comes after April 20, in half of years after May 3, and in 1 of 10 years after May 20 (NOAA 1991 to 2020 normals). The median last frost date is May 3. NOAA Climate Normals 1991-2020
  3. First fall frost (32°F) at this station: in 1 of 10 years the first frost comes before September 29, in half of years before October 13, and in 9 of 10 years before October 27 (NOAA 1991 to 2020 normals). The median first frost date is October 13. NOAA Climate Normals 1991-2020
  4. Growing season (days between the last spring and first fall 32°F frost) at this station: at least 138 days in 9 of 10 years, at least 160 days in half of years, and at least 179 days in 1 of 10 years. NOAA Climate Normals 1991-2020
  5. Frost dates on this page come from NOAA climate normals for the Ann Arbor U Of Mich weather station (USC00200230), 3.7 miles from the center of Ann Arbor at 813 feet, using 29 years of records from 1991 to 2020. NOAA Climate Normals 1991-2020
  6. Colorado State University Extension's vegetable planting guide (written for Colorado) groups broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips as hardy vegetables, with this rule: as early as 2-4 weeks before the average last... CSU Extension GardenNotes #720
  7. Hard freeze (28°F) at this station: the median last spring date is April 23 and the median first fall date is October 26. NOAA Climate Normals 1991-2020
  8. At this station the low reached 32°F or colder in 100% of years from 1991 to 2020, and 28°F or colder in 100% of years. NOAA Climate Normals 1991-2020
  9. Colorado State University Extension's vegetable planting guide (written for Colorado) groups beets, carrots, cauliflower, parsnips, potatoes, Swiss chard as semi-hardy vegetables, with this rule: as early as 0-2 weeks before the average last spring frost.... CSU Extension GardenNotes #720
  10. Colorado State University Extension's vegetable planting guide (written for Colorado) groups snap beans, sweet corn, cucumbers, summer squash as tender vegetables, with this rule: from seed around the average last spring frost; cucumber and summer squash... CSU Extension GardenNotes #720
  11. Colorado State University Extension's vegetable planting guide (written for Colorado) groups cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon as very tender vegetables, with this rule: typically 2 or more weeks after the average last... CSU Extension GardenNotes #720
  12. GardenFacts calculation: earliest planting date plus CSU days to harvest (table on this page), from the station's median last frost. NOAA Climate Normals 1991-2020
  13. CSU Extension vegetable table: soil temperature, depth, spacing, days to harvest (table on this page). CSU Extension GardenNotes #720
  14. USDA hardiness zones are based on the average annual extreme minimum winter temperature (the coldest night of each winter, averaged over 1991 to 2020 for the 2023 map), not on summer heat or frost dates. Each zone spans 10°F and each half zone (a or b)... USDA Plant Hardiness Zone Map
  15. Ann Arbor, Michigan overlaps 5 ZIP code areas. By land area, 100% lies in ZIP code areas rated zone 6a. USDA zone map 2023 (PRISM, OSU)

Frost dates are probabilities from 1991 to 2020 weather records at one NOAA station, not a forecast. Any year can be earlier or later. The hardiness zone describes the average coldest winter night, not frost dates or summer heat. Spots inside the city can differ (ZIP table). Planting rules come from Colorado State University Extension's guide, written for Colorado. A local extension office may give dates tuned to the area. Planting and harvest dates marked GardenFacts calculation are simple arithmetic from the facts above, not advice from the source.

Hardiness zone data: USDA Plant Hardiness Zone Map (2023), USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu, accessed October 30, 2026. This is not the official USDA map. Frost data: NOAA NCEI U.S. Climate Normals 1991-2020. Planting rules: Colorado State University Extension.