Frost dates Illinois Aurora

Frost dates in Aurora, Illinois

Last spring frost Apr 19 First fall frost Oct 23 NOAA 1991-2020

The average last spring frost in Aurora is Apr 19 and the average first fall frost is Oct 23, measured at AURORA, about 1 mile from the city centre. Below: how sure those dates are, and what to start, sow and set out each week.

Average last spring frostApr 1932°F, 50% probability
Average first fall frostOct 2332°F, 50% probability
Days between them187average 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 5Nov 3
50%Apr 19Oct 23
10%May 4Oct 9

Read it like this: in half of years the last 32°F freeze of spring comes after Apr 19, and in 1 year in 10 there is still a freeze after May 4. In 1 year in 10 the first fall freeze arrives before Oct 9.

Measured at: AURORA, IL (NOAA station USC00110338), about 1 mile away at 660 ft, 28 years of record in 1991-2020.

Other stations nearby, for comparison:

  • CHICAGO AURORA MUNI AP, IL (NOAA station USW00004808), about 8 miles away at 710 ft, 21 years of record in 1991-2020: last spring frost Apr 28, first fall frost Oct 13
  • WEST CHICAGO DUPAGE AP, IL (NOAA station USW00094892), about 11 miles away at 754 ft, 22 years of record in 1991-2020: last spring frost Apr 25, first fall frost Oct 19

Seed-starting schedule for Aurora, IL

Counted from a last frost date of Apr 19 (the average: a freeze comes later than this in half of years).

  1. Week of Jan 1114 weeks before last frost
    • Start seeds indoorsLeekJan 11 to Jan 25
    • Start seeds indoorsOnionJan 11 to Jan 25
  2. Week of Jan 1813 weeks before last frost
    • Start seeds indoorsParsleyJan 18 to Jan 25
  3. Week of Jan 2512 weeks before last frost
    • Start seeds indoorsCeleryJan 25 to Feb 8
    • Start seeds indoorsSpinachJan 25 to Feb 8
  4. Week of Feb 810 weeks before last frost
    • Start seeds indoorsBroccoliFeb 8 to Feb 22
    • Start seeds indoorsBrussels sproutFeb 8 to Feb 22
    • Start seeds indoorsCabbageFeb 8 to Feb 22
    • Start seeds indoorsKaleFeb 8 to Feb 22
    • Start seeds indoorsKohlrabiFeb 8 to Feb 22
  5. Week of Feb 159 weeks before last frost
    • Start seeds indoorsLettuceFeb 15 to Feb 22
  6. Week of Feb 228 weeks before last frost
    • Start seeds indoorsCauliflowerFeb 22 to Mar 8
    • Start seeds indoorsEggplantFeb 22 to Mar 8
    • Start seeds indoorsPepperFeb 22 to Mar 8
    • Start seeds indoorsSwiss chardFeb 22 to Mar 8
  7. Week of Mar 17 weeks before last frost
    • Start seeds indoorsTomatoMar 1 to Mar 15
  8. Week of Mar 86 weeks before last frost
    • Start seeds indoorsBasilMar 8 to Mar 22
    • Set transplants outSpinachMar 8 to Mar 29
  9. Week of Mar 224 weeks before last frost
    • Sow seed outdoorsRadishMar 22 to Apr 5
    • Sow seed outdoorsSwiss chardfrom Mar 22
    • Sow seed outdoorsTurnipMar 22 to Apr 5
    • Set transplants outBroccoliMar 22 to Apr 5
    • Set transplants outBrussels sproutMar 22 to Apr 5
    • Set transplants outCabbagefrom Mar 22
    • Set transplants outKalefrom Mar 22
    • Set transplants outKohlrabifrom Mar 22
    • Set transplants outLeekfrom Mar 22
    • Set transplants outLettuceMar 22 to Mar 29
    • Set transplants outOnionfrom Mar 22
  10. Week of Mar 293 weeks before last frost
    • Start seeds indoorsCucumberMar 29 to Apr 5
    • Set transplants outParsleyMar 29 to Apr 5
  11. Week of Apr 52 weeks before last frost
    • Start seeds indoorsMelonApr 5 to Apr 12
    • Start seeds indoorsPumpkinApr 5 to Apr 12
    • Start seeds indoorsSummer squashApr 5 to Apr 12
    • Start seeds indoorsWinter squashApr 5 to Apr 12
    • Start seeds indoorsZucchiniApr 5 to Apr 12
    • Plant seed potatoes outdoorsPotatoApr 5 to Apr 12
    • Set transplants outCauliflowerfrom Apr 5
    • Set transplants outSwiss chardfrom Apr 5
  12. Week of Apr 19Last frost week
    • Sow seed outdoorsBeanfrom Apr 19
    • Sow seed outdoorsParsnipfrom Apr 19
    • Set transplants outCeleryfrom Apr 19
  13. Week of Apr 261 week after last frost
    • Plant slips outdoorsSweet potatoApr 26 to May 3
    • Set transplants outCucumberApr 26 to May 3
    • Set transplants outTomatoApr 26 to May 3
  14. Week of May 32 weeks after last frost
    • Set transplants outBasilfrom May 3
    • Set transplants outEggplantMay 3 to May 10
    • Set transplants outMelonfrom May 3
    • Set transplants outPepperfrom May 3
    • Set transplants outPumpkinfrom May 3
    • Set transplants outSummer squashfrom May 3
    • Set transplants outWinter squashfrom May 3
    • Set transplants outZucchinifrom May 3

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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