Last frost date in O'Fallon, IL

Average last frost
April 12

In O'Fallon, the last spring frost comes around April 12 in an average year. Wait until April 28 if you want 90% odds of no more frost. The first fall frost usually arrives about October 20, which leaves 189 frost-free days. An early freeze before October 3 happens one year in ten.

Safe after (10% risk)
Apr 28
Average first frost
Oct 20
Frost-free season
189 days
Hard freeze (28°F) ends
Mar 31
Next 7 nights in O'Fallon

No frost in the next 7 nights

Later than usual: the average first frost here is October 20.

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

  1. ThuOct 2247°
  2. FriOct 2345°
  3. SatOct 2447°
  4. SunOct 2549°
  5. MonOct 2649°
  6. TueOct 2747°
  7. WedOct 2847°
JanFebMarAprMayJunJulAugSepOctNovDecLast frost Apr 12First frost Oct 20189 frost-free daysBlue: chance of 32°F frost. Green: average frost-free season.JFMAMJJASOND189 frost-free days
Frost risk through the year at Belleville Siu Rsch, 6.7 miles from O'Fallon.

Planting calendar for O'Fallon

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
TomatoesApr 19–May 3
PumpkinsApr 26–May 10
SunflowersApr 12–May 3
CucumbersApr 26–May 3
CornApr 19–May 3
Sweet potatoesMay 3–May 17
WatermelonApr 26–May 10
Green beansApr 19–May 10
ZucchiniApr 19–May 3
OkraMay 3–May 17
PeppersApr 26–May 10
BasilApr 19–May 3
Butternut squashApr 19–May 3
CantaloupeApr 26–May 10
EggplantApr 26–May 10
Cool-season crops
JanFebMarAprMayJunJulAugSepOctNovDec
PotatoesMar 15–Mar 29
OnionsMar 1–Mar 22
CarrotsMar 22–Apr 26
LettuceMar 29–Apr 19
BroccoliMar 15–Mar 29
BeetsMar 15–Apr 26
PeasMar 1–Mar 15
CabbageMar 15–Mar 29
RadishesMar 8–Apr 19
Brussels sproutsMar 29–Apr 12
SpinachMar 1–Mar 22
CilantroMar 29–Apr 19
KaleMar 15–Mar 29
Collard greensMar 15–Mar 29
TurnipsMar 15–Mar 29
DillApr 12–Apr 26
CeleryApr 19–Apr 26
CauliflowerMar 29–Apr 12
LeeksMar 29–Apr 12
Swiss chardMar 29–Apr 26
ParsleyMar 29–Apr 19
Fall bulbs and garlic
JanFebMarAprMayJunJulAugSepOctNovDec
Tulip bulbsOct 6–Nov 10
GarlicSep 29–Nov 3
Daffodil bulbsSep 22–Nov 3
Perennials
JanFebMarAprMayJunJulAugSepOctNovDec
StrawberriesMar 15–Mar 29
AsparagusMar 15–Mar 29

Frost probabilities

ThresholdSpring, 90% chance laterSpring, 50%Spring, 10%Fall, 10% chance earlierFall, 50%Fall, 90%
Light frost, 32°FMar 28Apr 12Apr 28Oct 3Oct 20Nov 1
Hard freeze, 28°FMar 14Mar 31Apr 16Oct 15Oct 30Nov 15

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 Belleville Siu Rsch (USW00013802) sits 6.7 miles from the center of O'Fallon at 450 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 O'Fallon, IL?

The average last frost date in O'Fallon is April 12, based on NOAA 1991–2020 climate normals. There is a 10% chance of frost after April 28.

When is the first frost in O'Fallon?

The first frost in fall usually comes around October 20. One year in ten it arrives before October 3.

How long is the growing season in O'Fallon?

About 189 days between the average last and first frost.

When should I plant tomatoes in O'Fallon?

Plant tomato seedlings outside from April 19 to May 3. Start seeds indoors six to eight weeks earlier.

Nearby in Illinois

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