Frost dates Illinois Chicago

Frost dates in Chicago, Illinois

Last spring frost Apr 10 First fall frost Nov 5 NOAA 1991-2020

The average last spring frost in Chicago is Apr 10 and the average first fall frost is Nov 5, measured at CHICAGO NORTHERLY IS, about 2 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 1032°F, 50% probability
Average first fall frostNov 532°F, 50% probability
Days between them209average 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%Mar 29Nov 20
50%Apr 10Nov 5
10%Apr 25Oct 24

Read it like this: in half of years the last 32°F freeze of spring comes after Apr 10, and in 1 year in 10 there is still a freeze after Apr 25. In 1 year in 10 the first fall freeze arrives before Oct 24.

Measured at: CHICAGO NORTHERLY IS, IL (NOAA station USC00111550), about 2 miles away at 583 ft, 15 years of record in 1991-2020.

Other stations nearby, for comparison:

  • CHICAGO MIDWAY AP, IL (NOAA station USW00014819), about 7 miles away at 612 ft, 23 years of record in 1991-2020: last spring frost Apr 11, first fall frost Oct 31
  • CHICAGO MIDWAY AP 3SW, IL (NOAA station USC00111577), about 10 miles away at 620 ft, 30 years of record in 1991-2020: last spring frost Apr 10, first fall frost Nov 1

Seed-starting schedule for Chicago, IL

Counted from a last frost date of Apr 10 (the average: a freeze comes later than this in half of years).

  1. Week of Jan 214 weeks before last frost
    • Start seeds indoorsLeekJan 2 to Jan 16
    • Start seeds indoorsOnionJan 2 to Jan 16
  2. Week of Jan 913 weeks before last frost
    • Start seeds indoorsParsleyJan 9 to Jan 16
  3. Week of Jan 1612 weeks before last frost
    • Start seeds indoorsCeleryJan 16 to Jan 30
    • Start seeds indoorsSpinachJan 16 to Jan 30
  4. Week of Jan 3010 weeks before last frost
    • Start seeds indoorsBroccoliJan 30 to Feb 13
    • Start seeds indoorsBrussels sproutJan 30 to Feb 13
    • Start seeds indoorsCabbageJan 30 to Feb 13
    • Start seeds indoorsKaleJan 30 to Feb 13
    • Start seeds indoorsKohlrabiJan 30 to Feb 13
  5. Week of Feb 69 weeks before last frost
    • Start seeds indoorsLettuceFeb 6 to Feb 13
  6. Week of Feb 138 weeks before last frost
    • Start seeds indoorsCauliflowerFeb 13 to Feb 27
    • Start seeds indoorsEggplantFeb 13 to Feb 27
    • Start seeds indoorsPepperFeb 13 to Feb 27
    • Start seeds indoorsSwiss chardFeb 13 to Feb 27
  7. Week of Feb 207 weeks before last frost
    • Start seeds indoorsTomatoFeb 20 to Mar 6
  8. Week of Feb 276 weeks before last frost
    • Start seeds indoorsBasilFeb 27 to Mar 13
    • Set transplants outSpinachFeb 27 to Mar 20
  9. Week of Mar 134 weeks before last frost
    • Sow seed outdoorsRadishMar 13 to Mar 27
    • Sow seed outdoorsSwiss chardfrom Mar 13
    • Sow seed outdoorsTurnipMar 13 to Mar 27
    • Set transplants outBroccoliMar 13 to Mar 27
    • Set transplants outBrussels sproutMar 13 to Mar 27
    • Set transplants outCabbagefrom Mar 13
    • Set transplants outKalefrom Mar 13
    • Set transplants outKohlrabifrom Mar 13
    • Set transplants outLeekfrom Mar 13
    • Set transplants outLettuceMar 13 to Mar 20
    • Set transplants outOnionfrom Mar 13
  10. Week of Mar 203 weeks before last frost
    • Start seeds indoorsCucumberMar 20 to Mar 27
    • Set transplants outParsleyMar 20 to Mar 27
  11. Week of Mar 272 weeks before last frost
    • Start seeds indoorsMelonMar 27 to Apr 3
    • Start seeds indoorsPumpkinMar 27 to Apr 3
    • Start seeds indoorsSummer squashMar 27 to Apr 3
    • Start seeds indoorsWinter squashMar 27 to Apr 3
    • Start seeds indoorsZucchiniMar 27 to Apr 3
    • Plant seed potatoes outdoorsPotatoMar 27 to Apr 3
    • Set transplants outCauliflowerfrom Mar 27
    • Set transplants outSwiss chardfrom Mar 27
  12. Week of Apr 10Last frost week
    • Sow seed outdoorsBeanfrom Apr 10
    • Sow seed outdoorsParsnipfrom Apr 10
    • Set transplants outCeleryfrom Apr 10
  13. Week of Apr 171 week after last frost
    • Plant slips outdoorsSweet potatoApr 17 to Apr 24
    • Set transplants outCucumberApr 17 to Apr 24
    • Set transplants outTomatoApr 17 to Apr 24
  14. Week of Apr 242 weeks after last frost
    • Set transplants outBasilfrom Apr 24
    • Set transplants outEggplantApr 24 to May 1
    • Set transplants outMelonfrom Apr 24
    • Set transplants outPepperfrom Apr 24
    • Set transplants outPumpkinfrom Apr 24
    • Set transplants outSummer squashfrom Apr 24
    • Set transplants outWinter squashfrom Apr 24
    • Set transplants outZucchinifrom Apr 24

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

More in Illinois

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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