Last frost date in Johnston, IA

Average last frost
April 19

In Johnston, the last spring frost comes around April 19 in an average year. Wait until May 3 if you want 90% odds of no more frost. The first fall frost usually arrives about October 18, which leaves 179 frost-free days. An early freeze before October 1 happens one year in ten.

Safe after (10% risk)
May 3
Average first frost
Oct 18
Frost-free season
179 days
Hard freeze (28°F) ends
Apr 9
Next 7 nights in Johnston

No frost in the next 7 nights

Later than usual: the average first frost here is October 18.

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

  1. ThuOct 2254°
  2. FriOct 2357°
  3. SatOct 2455°
  4. SunOct 2552°
  5. MonOct 2646°
  6. TueOct 2744°
  7. WedOct 2845°
JanFebMarAprMayJunJulAugSepOctNovDecLast frost Apr 19First frost Oct 18179 frost-free daysBlue: chance of 32°F frost. Green: average frost-free season.JFMAMJJASOND179 frost-free days
Frost risk through the year at Des Moines Wsfo-johnston, 3.1 miles from Johnston.

Planting calendar for Johnston

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
TomatoesApr 26–May 10
PumpkinsMay 3–May 17
SunflowersApr 19–May 10
CucumbersMay 3–May 10
CornApr 26–May 10
Sweet potatoesMay 10–May 24
WatermelonMay 3–May 17
Green beansApr 26–May 17
ZucchiniApr 26–May 10
OkraMay 10–May 24
PeppersMay 3–May 17
BasilApr 26–May 10
Butternut squashApr 26–May 10
CantaloupeMay 3–May 17
EggplantMay 3–May 17
Cool-season crops
JanFebMarAprMayJunJulAugSepOctNovDec
PotatoesMar 22–Apr 5
OnionsMar 8–Mar 29
CarrotsMar 29–May 3
LettuceApr 5–Apr 26
BroccoliMar 22–Apr 5
BeetsMar 22–May 3
PeasMar 8–Mar 22
CabbageMar 22–Apr 5
RadishesMar 15–Apr 26
Brussels sproutsApr 5–Apr 19
SpinachMar 8–Mar 29
CilantroApr 5–Apr 26
KaleMar 22–Apr 5
Collard greensMar 22–Apr 5
TurnipsMar 22–Apr 5
DillApr 19–May 3
CeleryApr 26–May 3
CauliflowerApr 5–Apr 19
LeeksApr 5–Apr 19
Swiss chardApr 5–May 3
ParsleyApr 5–Apr 26
Fall bulbs and garlic
JanFebMarAprMayJunJulAugSepOctNovDec
Tulip bulbsOct 4–Nov 8
GarlicSep 27–Nov 1
Daffodil bulbsSep 20–Nov 1
Perennials
JanFebMarAprMayJunJulAugSepOctNovDec
StrawberriesMar 22–Apr 5
AsparagusMar 22–Apr 5

Frost probabilities

ThresholdSpring, 90% chance laterSpring, 50%Spring, 10%Fall, 10% chance earlierFall, 50%Fall, 90%
Light frost, 32°FApr 5Apr 19May 3Oct 1Oct 18Oct 30
Hard freeze, 28°FMar 25Apr 9Apr 23Oct 14Oct 27Nov 9

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 Des Moines Wsfo-johnston (USC00132209) sits 3.1 miles from the center of Johnston at 959 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 Johnston, IA?

The average last frost date in Johnston is April 19, based on NOAA 1991–2020 climate normals. There is a 10% chance of frost after May 3.

When is the first frost in Johnston?

The first frost in fall usually comes around October 18. One year in ten it arrives before October 1.

How long is the growing season in Johnston?

About 179 days between the average last and first frost.

When should I plant tomatoes in Johnston?

Plant tomato seedlings outside from April 26 to May 10. Start seeds indoors six to eight weeks earlier.

Nearby in Iowa

All 27 cities in Iowa