Last frost date in Altadena, CA

Average last frost

January 8

Expect the last frost in Altadena around January 8. Frost after February 17 happens in only one year out of ten. The first fall frost usually arrives about January 7, which leaves 365 frost-free days. An early freeze before December 20 happens one year in ten.

Safe after (10% risk): Feb 17
Average first frost: Jan 7
Frost-free season: 365 days
Hard freeze (28°F) ends: rare

Next 6 nights in Altadena

No frost in the next 6 nights

National Weather Service forecast, updated Oct 22, 12:24 UTC

ThuOct 2252°
FriOct 2354°
SatOct 2457°
SunOct 2559°
MonOct 2659°
TueOct 2759°

Frost risk through the year at Pasadena, 3.1 miles from Altadena.

Planting calendar for Altadena

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

Start indoorsPlant outSow outdoorsFall plantingAverage last and first frost

Warm-season crops

JanFebMarAprMayJunJulAugSepOctNovDec

TomatoesFeb 15–Mar 1

PumpkinsFeb 15–Mar 1

SunflowersFeb 15–Mar 8

CucumbersFeb 22–Mar 1

CornFeb 15–Mar 1

Sweet potatoesFeb 15–Mar 1

WatermelonFeb 15–Mar 1

Green beansFeb 15–Mar 8

ZucchiniFeb 15–Mar 1

OkraFeb 15–Mar 1

PeppersFeb 15–Mar 1

BasilFeb 15–Mar 1

Butternut squashFeb 15–Mar 1

CantaloupeFeb 15–Mar 1

EggplantFeb 15–Mar 1

Cool-season crops

JanFebMarAprMayJunJulAugSepOctNovDec

PotatoesDec 11–Dec 25

OnionsNov 27–Dec 18

CarrotsDec 18–Jan 22

LettuceDec 25–Jan 15

BroccoliDec 11–Dec 25

BeetsDec 11–Jan 22

PeasNov 27–Dec 11

CabbageDec 11–Dec 25

RadishesDec 4–Jan 15

Brussels sproutsDec 25–Jan 8

SpinachNov 27–Dec 18

CilantroDec 25–Jan 15

KaleDec 11–Dec 25

Collard greensDec 11–Dec 25

TurnipsDec 11–Dec 25

DillJan 8–Jan 22

CeleryJan 15–Jan 22

CauliflowerDec 25–Jan 8

LeeksDec 25–Jan 8

Swiss chardDec 25–Jan 22

ParsleyDec 25–Jan 15

Fall bulbs and garlic

JanFebMarAprMayJunJulAugSepOctNovDec

Tulip bulbsDec 15–Jan 15

GarlicOct 15–Nov 30

Daffodil bulbsOct 15–Nov 30

Perennials

JanFebMarAprMayJunJulAugSepOctNovDec

StrawberriesDec 11–Dec 25

AsparagusDec 11–Dec 25

Frost probabilities

Threshold	Spring, 90% chance later	Spring, 50%	Spring, 10%	Fall, 10% chance earlier	Fall, 50%	Fall, 90%
Light frost, 32°F	Dec 20	Jan 8	Feb 17	Dec 20	Jan 7	Feb 14

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 Pasadena (USC00046719) sits 3.1 miles from the center of Altadena at 864 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 Altadena, CA?

The average last frost date in Altadena is January 8, based on NOAA 1991–2020 climate normals. There is a 10% chance of frost after February 17.

When is the first frost in Altadena?

The first frost in fall usually comes around January 7. One year in ten it arrives before December 20.

How long is the growing season in Altadena?

About 365 days between the average last and first frost.

When should I plant tomatoes in Altadena?

Plant tomato seedlings outside from February 15 to March 1. Start seeds indoors six to eight weeks earlier.

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