Last frost date in Allentown, PA

Average last frost
April 20

Expect the last frost in Allentown around April 20. Frost after May 6 happens in only one year out of ten. The first fall frost usually arrives about October 24, which leaves 184 frost-free days. An early freeze before October 8 happens one year in ten.

Safe after (10% risk)
May 6
Average first frost
Oct 24
Frost-free season
184 days
Hard freeze (28°F) ends
Apr 5
Next 7 nights in Allentown

Frost likely Fri night, low 32°F

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

  1. ThuOct 2239°
  2. FriOct 2332°frost
  3. SatOct 2433°possible frost
  4. SunOct 2536°possible frost
  5. MonOct 2643°
  6. TueOct 2743°
  7. WedOct 2843°
JanFebMarAprMayJunJulAugSepOctNovDecLast frost Apr 20First frost Oct 24184 frost-free daysBlue: chance of 32°F frost. Green: average frost-free season.JFMAMJJASOND184 frost-free days
Frost risk through the year at Allentown International Airport, 4.2 miles from Allentown.

Planting calendar for Allentown

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

Start indoorsPlant outSow outdoorsFall plantingAverage last and first frost
Warm-season crops
JanFebMarAprMayJunJulAugSepOctNovDec
TomatoesApr 27–May 11
PumpkinsMay 4–May 18
SunflowersApr 20–May 11
CucumbersMay 4–May 11
CornApr 27–May 11
Sweet potatoesMay 11–May 25
WatermelonMay 4–May 18
Green beansApr 27–May 18
ZucchiniApr 27–May 11
OkraMay 11–May 25
PeppersMay 4–May 18
BasilApr 27–May 11
Butternut squashApr 27–May 11
CantaloupeMay 4–May 18
EggplantMay 4–May 18
Cool-season crops
JanFebMarAprMayJunJulAugSepOctNovDec
PotatoesMar 23–Apr 6
OnionsMar 9–Mar 30
CarrotsMar 30–May 4
LettuceApr 6–Apr 27
BroccoliMar 23–Apr 6
BeetsMar 23–May 4
PeasMar 9–Mar 23
CabbageMar 23–Apr 6
RadishesMar 16–Apr 27
Brussels sproutsApr 6–Apr 20
SpinachMar 9–Mar 30
CilantroApr 6–Apr 27
KaleMar 23–Apr 6
Collard greensMar 23–Apr 6
TurnipsMar 23–Apr 6
DillApr 20–May 4
CeleryApr 27–May 4
CauliflowerApr 6–Apr 20
LeeksApr 6–Apr 20
Swiss chardApr 6–May 4
ParsleyApr 6–Apr 27
Fall bulbs and garlic
JanFebMarAprMayJunJulAugSepOctNovDec
Tulip bulbsOct 10–Nov 14
GarlicOct 3–Nov 7
Daffodil bulbsSep 26–Nov 7
Perennials
JanFebMarAprMayJunJulAugSepOctNovDec
StrawberriesMar 23–Apr 6
AsparagusMar 23–Apr 6

Frost probabilities

ThresholdSpring, 90% chance laterSpring, 50%Spring, 10%Fall, 10% chance earlierFall, 50%Fall, 90%
Light frost, 32°FApr 6Apr 20May 6Oct 8Oct 24Nov 6
Hard freeze, 28°FMar 23Apr 5Apr 18Oct 19Nov 4Nov 18

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 Allentown International Airport (USW00014737) sits 4.2 miles from the center of Allentown at 390 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 Allentown, PA?

The average last frost date in Allentown is April 20, based on NOAA 1991–2020 climate normals. There is a 10% chance of frost after May 6.

When is the first frost in Allentown?

The first frost in fall usually comes around October 24. One year in ten it arrives before October 8.

How long is the growing season in Allentown?

About 184 days between the average last and first frost.

When should I plant tomatoes in Allentown?

Plant tomato seedlings outside from April 27 to May 11. Start seeds indoors six to eight weeks earlier.

Nearby in Pennsylvania

All 35 cities in Pennsylvania