Last frost date in Mason City, IA

Average last frost
April 29

The average last frost in Mason City is April 29. By May 9 the chance of another 32°F night drops to 1 in 10. The first fall frost usually arrives about October 7, which leaves 161 frost-free days. An early freeze before September 25 happens one year in ten.

Safe after (10% risk)
May 9
Average first frost
Oct 7
Frost-free season
161 days
Hard freeze (28°F) ends
Apr 18
Next 7 nights in Mason City

No frost in the next 7 nights

Later than usual: the average first frost here is October 7.

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

  1. ThuOct 2252°
  2. FriOct 2355°
  3. SatOct 2451°
  4. SunOct 2545°
  5. MonOct 2641°
  6. TueOct 2739°
  7. WedOct 2841°
JanFebMarAprMayJunJulAugSepOctNovDecLast frost Apr 29First frost Oct 7161 frost-free daysBlue: chance of 32°F frost. Green: average frost-free season.JFMAMJJASOND161 frost-free days
Frost risk through the year at Mason City, 1.1 miles from Mason City.

Planting calendar for Mason City

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

Start indoorsPlant outSow outdoorsFall plantingAverage last and first frost
Warm-season crops
JanFebMarAprMayJunJulAugSepOctNovDec
TomatoesMay 6–May 20
PumpkinsMay 13–May 27
SunflowersApr 29–May 20
CucumbersMay 13–May 20
CornMay 6–May 20
Sweet potatoesMay 20–Jun 3
WatermelonMay 13–May 27
Green beansMay 6–May 27
ZucchiniMay 6–May 20
OkraMay 20–Jun 3
PeppersMay 13–May 27
BasilMay 6–May 20
Butternut squashMay 6–May 20
CantaloupeMay 13–May 27
EggplantMay 13–May 27
Cool-season crops
JanFebMarAprMayJunJulAugSepOctNovDec
PotatoesApr 1–Apr 15
OnionsMar 18–Apr 8
CarrotsApr 8–May 13
LettuceApr 15–May 6
BroccoliApr 1–Apr 15
BeetsApr 1–May 13
PeasMar 18–Apr 1
CabbageApr 1–Apr 15
RadishesMar 25–May 6
Brussels sproutsApr 15–Apr 29
SpinachMar 18–Apr 8
CilantroApr 15–May 6
KaleApr 1–Apr 15
Collard greensApr 1–Apr 15
TurnipsApr 1–Apr 15
DillApr 29–May 13
CeleryMay 6–May 13
CauliflowerApr 15–Apr 29
LeeksApr 15–Apr 29
Swiss chardApr 15–May 13
ParsleyApr 15–May 6
Fall bulbs and garlic
JanFebMarAprMayJunJulAugSepOctNovDec
Tulip bulbsSep 23–Oct 28
GarlicSep 16–Oct 21
Daffodil bulbsSep 9–Oct 21
Perennials
JanFebMarAprMayJunJulAugSepOctNovDec
StrawberriesApr 1–Apr 15
AsparagusApr 1–Apr 15

Frost probabilities

ThresholdSpring, 90% chance laterSpring, 50%Spring, 10%Fall, 10% chance earlierFall, 50%Fall, 90%
Light frost, 32°FApr 14Apr 29May 9Sep 25Oct 7Oct 21
Hard freeze, 28°FApr 3Apr 18Apr 30Oct 1Oct 18Oct 31

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 Mason City (USC00135230) sits 1.1 miles from the center of Mason City at 1,105 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 Mason City, IA?

The average last frost date in Mason City is April 29, based on NOAA 1991–2020 climate normals. There is a 10% chance of frost after May 9.

When is the first frost in Mason City?

The first frost in fall usually comes around October 7. One year in ten it arrives before September 25.

How long is the growing season in Mason City?

About 161 days between the average last and first frost.

When should I plant tomatoes in Mason City?

Plant tomato seedlings outside from May 6 to May 20. Start seeds indoors six to eight weeks earlier.

Nearby in Iowa

All 27 cities in Iowa