Last frost date in Zion, IL

Average last frost
April 30

The average last frost in Zion is April 30. By May 16 the chance of another 32°F night drops to 1 in 10. The first fall frost usually arrives about October 21, which leaves 173 frost-free days. An early freeze before October 5 happens one year in ten.

Safe after (10% risk)
May 16
Average first frost
Oct 21
Frost-free season
173 days
Hard freeze (28°F) ends
Apr 16
Next 7 nights in Zion

No frost in the next 7 nights

Later than usual: the average first frost here is October 21.

National Weather Service forecast, updated Oct 22, 12:57 UTC

  1. ThuOct 2248°
  2. FriOct 2349°
  3. SatOct 2451°
  4. SunOct 2551°
  5. MonOct 2647°
  6. TueOct 2745°
  7. WedOct 2845°
JanFebMarAprMayJunJulAugSepOctNovDecLast frost Apr 30First frost Oct 21173 frost-free daysBlue: chance of 32°F frost. Green: average frost-free season.JFMAMJJASOND173 frost-free days
Frost risk through the year at Chicago Waukegan Regional Airport, 3.1 miles from Zion.

Planting calendar for Zion

Windows count forward or back from the average frost dates above. Click a crop for dates across Illinois.

Start indoorsPlant outSow outdoorsFall plantingAverage last and first frost
Warm-season crops
JanFebMarAprMayJunJulAugSepOctNovDec
TomatoesMay 7–May 21
PumpkinsMay 14–May 28
SunflowersApr 30–May 21
CucumbersMay 14–May 21
CornMay 7–May 21
Sweet potatoesMay 21–Jun 4
WatermelonMay 14–May 28
Green beansMay 7–May 28
ZucchiniMay 7–May 21
OkraMay 21–Jun 4
PeppersMay 14–May 28
BasilMay 7–May 21
Butternut squashMay 7–May 21
CantaloupeMay 14–May 28
EggplantMay 14–May 28
Cool-season crops
JanFebMarAprMayJunJulAugSepOctNovDec
PotatoesApr 2–Apr 16
OnionsMar 19–Apr 9
CarrotsApr 9–May 14
LettuceApr 16–May 7
BroccoliApr 2–Apr 16
BeetsApr 2–May 14
PeasMar 19–Apr 2
CabbageApr 2–Apr 16
RadishesMar 26–May 7
Brussels sproutsApr 16–Apr 30
SpinachMar 19–Apr 9
CilantroApr 16–May 7
KaleApr 2–Apr 16
Collard greensApr 2–Apr 16
TurnipsApr 2–Apr 16
DillApr 30–May 14
CeleryMay 7–May 14
CauliflowerApr 16–Apr 30
LeeksApr 16–Apr 30
Swiss chardApr 16–May 14
ParsleyApr 16–May 7
Fall bulbs and garlic
JanFebMarAprMayJunJulAugSepOctNovDec
Tulip bulbsOct 7–Nov 11
GarlicSep 30–Nov 4
Daffodil bulbsSep 23–Nov 4
Perennials
JanFebMarAprMayJunJulAugSepOctNovDec
StrawberriesApr 2–Apr 16
AsparagusApr 2–Apr 16

Frost probabilities

ThresholdSpring, 90% chance laterSpring, 50%Spring, 10%Fall, 10% chance earlierFall, 50%Fall, 90%
Light frost, 32°FApr 14Apr 30May 16Oct 5Oct 21Nov 2
Hard freeze, 28°FApr 2Apr 16May 2Oct 15Nov 1Nov 14

Read the spring 10% column as the date after which only one year in ten still gets frost. That is the safer date for tomatoes, peppers and basil.

Where these numbers come from

NOAA station Chicago Waukegan Regional Airport (USW00014880) sits 3.1 miles from the center of Zion at 727 feet. Its averages cover 1991 to 2020. Low spots, valleys and open fields can keep getting frost a week or two after the station stops; city centers and lakeshores usually get less of it.

Questions

When is the last frost in Zion, IL?

The average last frost date in Zion is April 30, based on NOAA 1991–2020 climate normals. There is a 10% chance of frost after May 16.

When is the first frost in Zion?

The first frost in fall usually comes around October 21. One year in ten it arrives before October 5.

How long is the growing season in Zion?

About 173 days between the average last and first frost.

When should I plant tomatoes in Zion?

Plant tomato seedlings outside from May 7 to May 21. Start seeds indoors six to eight weeks earlier.

Nearby in Illinois

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