Frost dates Michigan Detroit

Frost dates in Detroit, Michigan

Last spring frost Apr 21 First fall frost Oct 31 NOAA 1991-2020

The average last spring frost in Detroit is Apr 21 and the average first fall frost is Oct 31, measured at DETROIT CITY AP, about 6 miles from the city centre. Below: how sure those dates are, and what to start, sow and set out each week.

Average last spring frostApr 2132°F, 50% probability
Average first fall frostOct 3132°F, 50% probability
Days between them193average frost-free season
How sure is that date? NOAA probability levels for a 32°F freeze
ProbabilityFreeze still comes after (spring)First freeze has come by (fall)
90%Apr 7Nov 11
50%Apr 21Oct 31
10%May 6Oct 17

Read it like this: in half of years the last 32°F freeze of spring comes after Apr 21, and in 1 year in 10 there is still a freeze after May 6. In 1 year in 10 the first fall freeze arrives before Oct 17.

Measured at: DETROIT CITY AP, MI (NOAA station USW00014822), about 6 miles away at 626 ft, 29 years of record in 1991-2020.

Other stations nearby, for comparison:

  • DEARBORN #2, MI (NOAA station USC00202016), about 7 miles away at 605 ft, 14 years of record in 1991-2020: last spring frost Apr 27, first fall frost Oct 25
  • GROSSE POINTE FARMS, MI (NOAA station USC00203477), about 10 miles away at 613 ft, 23 years of record in 1991-2020: last spring frost Apr 29, first fall frost Oct 22

Seed-starting schedule for Detroit, MI

Counted from a last frost date of Apr 21 (the average: a freeze comes later than this in half of years).

  1. Week of Jan 1314 weeks before last frost
    • Start seeds indoorsLeekJan 13 to Jan 27
    • Start seeds indoorsOnionJan 13 to Jan 27
  2. Week of Jan 2013 weeks before last frost
    • Start seeds indoorsParsleyJan 20 to Jan 27
  3. Week of Jan 2712 weeks before last frost
    • Start seeds indoorsCeleryJan 27 to Feb 10
    • Start seeds indoorsSpinachJan 27 to Feb 10
  4. Week of Feb 1010 weeks before last frost
    • Start seeds indoorsBroccoliFeb 10 to Feb 24
    • Start seeds indoorsBrussels sproutFeb 10 to Feb 24
    • Start seeds indoorsCabbageFeb 10 to Feb 24
    • Start seeds indoorsKaleFeb 10 to Feb 24
    • Start seeds indoorsKohlrabiFeb 10 to Feb 24
  5. Week of Feb 179 weeks before last frost
    • Start seeds indoorsLettuceFeb 17 to Feb 24
  6. Week of Feb 248 weeks before last frost
    • Start seeds indoorsCauliflowerFeb 24 to Mar 10
    • Start seeds indoorsEggplantFeb 24 to Mar 10
    • Start seeds indoorsPepperFeb 24 to Mar 10
    • Start seeds indoorsSwiss chardFeb 24 to Mar 10
  7. Week of Mar 37 weeks before last frost
    • Start seeds indoorsTomatoMar 3 to Mar 17
  8. Week of Mar 106 weeks before last frost
    • Start seeds indoorsBasilMar 10 to Mar 24
    • Set transplants outSpinachMar 10 to Mar 31
  9. Week of Mar 244 weeks before last frost
    • Sow seed outdoorsRadishMar 24 to Apr 7
    • Sow seed outdoorsSwiss chardfrom Mar 24
    • Sow seed outdoorsTurnipMar 24 to Apr 7
    • Set transplants outBroccoliMar 24 to Apr 7
    • Set transplants outBrussels sproutMar 24 to Apr 7
    • Set transplants outCabbagefrom Mar 24
    • Set transplants outKalefrom Mar 24
    • Set transplants outKohlrabifrom Mar 24
    • Set transplants outLeekfrom Mar 24
    • Set transplants outLettuceMar 24 to Mar 31
    • Set transplants outOnionfrom Mar 24
  10. Week of Mar 313 weeks before last frost
    • Start seeds indoorsCucumberMar 31 to Apr 7
    • Set transplants outParsleyMar 31 to Apr 7
  11. Week of Apr 72 weeks before last frost
    • Start seeds indoorsMelonApr 7 to Apr 14
    • Start seeds indoorsPumpkinApr 7 to Apr 14
    • Start seeds indoorsSummer squashApr 7 to Apr 14
    • Start seeds indoorsWinter squashApr 7 to Apr 14
    • Start seeds indoorsZucchiniApr 7 to Apr 14
    • Plant seed potatoes outdoorsPotatoApr 7 to Apr 14
    • Set transplants outCauliflowerfrom Apr 7
    • Set transplants outSwiss chardfrom Apr 7
  12. Week of Apr 21Last frost week
    • Sow seed outdoorsBeanfrom Apr 21
    • Sow seed outdoorsParsnipfrom Apr 21
    • Set transplants outCeleryfrom Apr 21
  13. Week of Apr 281 week after last frost
    • Plant slips outdoorsSweet potatoApr 28 to May 5
    • Set transplants outCucumberApr 28 to May 5
    • Set transplants outTomatoApr 28 to May 5
  14. Week of May 52 weeks after last frost
    • Set transplants outBasilfrom May 5
    • Set transplants outEggplantMay 5 to May 12
    • Set transplants outMelonfrom May 5
    • Set transplants outPepperfrom May 5
    • Set transplants outPumpkinfrom May 5
    • Set transplants outSummer squashfrom May 5
    • Set transplants outWinter squashfrom May 5
    • Set transplants outZucchinifrom May 5

Not in the city centre? Look up your own ZIP code

Where the numbers come from

Sources and method

Frost dates. U.S. Climate Normals 2020: U.S. Annual/Seasonal Climate Normals (1991-2020), NOAA National Centers for Environmental Information (Palecki, Durre, Applequist, Arguez and Lawrimore, 2021). These are 30-year station statistics for 1991 to 2020. "Frost" here means an air temperature of 32°F or lower at the station. We use 6,539 stations that have at least 10 years of record and a published date; 176 more are stations where a freeze is too rare for NOAA to date, and 180 are stations cold enough to have frost risk all year.

Probability level. The headline dates are NOAA's 50% level: in half of years the last spring freeze comes later than that date, and in half of years the first fall freeze comes earlier. The 10% and 90% levels are shown next to them. For tender plants, the 10% spring date is the safer one to plan from: a freeze follows it in only 1 year in 10.

Which station. Your ZIP code is matched to the nearest of those stations by straight-line distance from the ZIP code's centre point (GeoNames, geonames.org, CC BY 4.0; 40,979 ZIP codes in the 50 states and DC). Nearest is not always most alike: a station on a hill, in a valley or by the water can differ from your garden by a week or more. That is why the station's name, distance and elevation are shown with every result, along with two more stations nearby. NOAA makes the same point: the normals are limited between stations as distance grows horizontally and vertically.

Seed-starting offsets. Growing Vegetables: When to Plant Your Vegetable Garden, a fact sheet from University of New Hampshire Extension. It gives each crop's weeks from seed to transplant and when it is safe to set out or sow relative to the last frost. The method is theirs too: take the planting date and count back the seed-to-transplant weeks. Where the fact sheet gives a range of planting dates, the start-indoors dates count back from the earliest one. The figures used, as the fact sheet states them:

  • Basil: Seed to transplant 6-8 weeks; set out 2 weeks after last frost.
  • Bean: Plant seed in garden after last frost.
  • Broccoli: Seed to transplant 4-6 weeks; set out 2-4 weeks before last frost.
  • Brussels sprout: Seed to transplant 4-6 weeks; set out 2-4 weeks before last frost.
  • Cabbage: Seed to transplant 4-6 weeks; set out 4 weeks before last frost.
  • Cauliflower: Seed to transplant 4-6 weeks; set out 2 weeks before last frost.
  • Celery: Seed to transplant 10-12 weeks; set out after last frost.
  • Cucumber: Seed to transplant 3-4 weeks; set out 1-2 weeks after last frost.
  • Eggplant: Seed to transplant 8-10 weeks; set out 2-3 weeks after last frost.
  • Kale: Seed to transplant 4-6 weeks; set out 4 weeks before last frost.
  • Kohlrabi: Seed to transplant 4-6 weeks; set out 4 weeks before last frost.
  • Leek: Seed to transplant 8-10 weeks; set out 4 weeks before last frost.
  • Lettuce: Seed to transplant 4-5 weeks; set out 3-4 weeks before last frost.
  • Melon: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.
  • Onion: Seed to transplant 8-10 weeks; set out 4 weeks before last frost.
  • Parsley: Seed to transplant 9-10 weeks; set out 2-3 weeks before last frost.
  • Parsnip: Plant seed in garden after last frost.
  • Pepper: Seed to transplant 8-10 weeks; set out 2 weeks after last frost.
  • Potato: Plant seed potatoes in garden 1-2 weeks before last frost.
  • Pumpkin: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.
  • Radish: Plant seed in garden 2-4 weeks before last frost.
  • Spinach: Seed to transplant 4-6 weeks; set out 3-6 weeks before last frost.
  • Summer squash: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.
  • Sweet potato: Plant slips in garden 1-2 weeks after last frost.
  • Swiss chard: Seed to transplant 4-6 weeks; set out 2 weeks before last frost; or plant seed in garden 4 weeks before last frost.
  • Tomato: Seed to transplant 6-8 weeks; set out 1-2 weeks after last frost.
  • Turnip: Plant seed in garden 2-4 weeks before last frost.
  • Winter squash: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.
  • Zucchini: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.

Not on the calendar. The same fact sheet times these by soil temperature, not by frost date, so they get no date here:

  • Pea: as soon as the soil thaws.
  • Beet: when the soil warms to 45°F.
  • Carrot: when the soil warms to 60°F.
  • Corn: when the soil warms to 60°F.
  • Cucumber, pumpkin, summer squash, winter squash, zucchini: direct-sow when the soil warms to 70°F.

Rutabaga is left out: the fact sheet gives it New Hampshire calendar dates, not a frost offset.

The fact sheet was written for New Hampshire. The offsets are relative to the last frost, so they carry to other places with a spring frost, but where winters are mild many cool-season crops are grown in fall and winter instead. Your state's extension service has the local calendar. Dates are 30-year statistics, not a forecast: check the forecast before setting tender plants out.

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