Last frost date in Ammon, ID

Average last frost
May 9

The average last frost in Ammon is May 9. By June 2 the chance of another 32°F night drops to 1 in 10. The first fall frost usually arrives about October 1, which leaves 142 frost-free days. An early freeze before September 17 happens one year in ten.

Safe after (10% risk)
Jun 2
Average first frost
Oct 1
Frost-free season
142 days
Hard freeze (28°F) ends
Apr 28
Next 7 nights in Ammon

Frost possible in low spots Fri night, low 36°F

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

  1. ThuOct 2246°
  2. FriOct 2336°possible frost
  3. SatOct 2433°possible frost
  4. SunOct 2535°possible frost
  5. MonOct 2635°possible frost
  6. TueOct 2734°possible frost
  7. WedOct 2835°possible frost
JanFebMarAprMayJunJulAugSepOctNovDecLast frost May 9First frost Oct 1142 frost-free daysBlue: chance of 32°F frost. Green: average frost-free season.JFMAMJJASOND142 frost-free days
Frost risk through the year at Idaho Falls - Kifi, 3.8 miles from Ammon.

Planting calendar for Ammon

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

Start indoorsPlant outSow outdoorsFall plantingAverage last and first frost
Warm-season crops
JanFebMarAprMayJunJulAugSepOctNovDec
TomatoesMay 16–May 30
PumpkinsMay 23–Jun 6
SunflowersMay 9–May 30
CucumbersMay 23–May 30
CornMay 16–May 30
Sweet potatoesMay 30–Jun 13
WatermelonMay 23–Jun 6
Green beansMay 16–Jun 6
ZucchiniMay 16–May 30
OkraMay 30–Jun 13
PeppersMay 23–Jun 6
BasilMay 16–May 30
Butternut squashMay 16–May 30
CantaloupeMay 23–Jun 6
EggplantMay 23–Jun 6
Cool-season crops
JanFebMarAprMayJunJulAugSepOctNovDec
PotatoesApr 11–Apr 25
OnionsMar 28–Apr 18
CarrotsApr 18–May 23
LettuceApr 25–May 16
BroccoliApr 11–Apr 25
BeetsApr 11–May 23
PeasMar 28–Apr 11
CabbageApr 11–Apr 25
RadishesApr 4–May 16
Brussels sproutsApr 25–May 9
SpinachMar 28–Apr 18
CilantroApr 25–May 16
KaleApr 11–Apr 25
Collard greensApr 11–Apr 25
TurnipsApr 11–Apr 25
DillMay 9–May 23
CeleryMay 16–May 23
CauliflowerApr 25–May 9
LeeksApr 25–May 9
Swiss chardApr 25–May 23
ParsleyApr 25–May 16
Fall bulbs and garlic
JanFebMarAprMayJunJulAugSepOctNovDec
Tulip bulbsSep 17–Oct 22
GarlicSep 10–Oct 15
Daffodil bulbsSep 3–Oct 15
Perennials
JanFebMarAprMayJunJulAugSepOctNovDec
StrawberriesApr 11–Apr 25
AsparagusApr 11–Apr 25

Frost probabilities

ThresholdSpring, 90% chance laterSpring, 50%Spring, 10%Fall, 10% chance earlierFall, 50%Fall, 90%
Light frost, 32°FApr 27May 9Jun 2Sep 17Oct 1Oct 15
Hard freeze, 28°FApr 11Apr 28May 11Sep 27Oct 13Oct 27

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 Idaho Falls - Kifi (USC00104455) sits 3.8 miles from the center of Ammon at 4,742 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 Ammon, ID?

The average last frost date in Ammon is May 9, based on NOAA 1991–2020 climate normals. There is a 10% chance of frost after June 2.

When is the first frost in Ammon?

The first frost in fall usually comes around October 1. One year in ten it arrives before September 17.

How long is the growing season in Ammon?

About 142 days between the average last and first frost.

When should I plant tomatoes in Ammon?

Plant tomato seedlings outside from May 16 to May 30. Start seeds indoors six to eight weeks earlier.

Nearby in Idaho

All 16 cities in Idaho