Frost dates for 91001 — Altadena, CA
Frost is light and occasional here — typically a few cold nights around midwinter (about 0 a year). Cover tender plants when frost is forecast.
How Altadena compares
- In a typical year, frost nights in Altadena fall between January 7 and January 8. In 1 year in 10 the first frost comes as early as December 20, or the last frost as late as February 17.
- Altadena shares its weather station with Pasadena, CA, 5 km away, so the two have the same frost dates.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | December 20 |
| 50% (median) | January 8 |
| 10% (safe for tender plants) | February 17 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | December 20 |
| 50% (median) | January 7 |
| 90% (late) | February 14 |
Frost here means 32°F (0°C). A median date means half of years have their last frost earlier and half later.
Gardening where frost is rare
Altadena, CA only freezes on a few winter nights, so the usual "plant after the last frost" rule doesn't apply. Heat and rainfall decide the seasons instead:
- Cool-season crops (lettuce, broccoli, peas, carrots) grow best from fall through late winter.
- Warm-season crops (tomatoes, peppers, beans, squash) do best planted in late winter to spring, and again in late summer for a fall crop — midsummer heat can stop tomatoes setting fruit.
- Heat lovers (okra, sweet potatoes, melons) can be planted through spring and early summer.
About these dates
Based on 1991–2020 NOAA climate normals for the Pasadena, CA weather station, 5 km away (elevation 863 ft (263 m)).
ZIP codes in Altadena: 91001 91003
Frost dates near Altadena
- Pasadena Jan 8 · Jan 7
- La Canada Flintridge Jan 8 · Jan 7
- Mount Wilson Apr 28 · Nov 15
- San Marino Jan 4 · Jan 2
- Montrose Jan 8 · Jan 7
- Sierra Madre Apr 28 · Nov 15
- South Pasadena Jan 8 · Jan 7
- Verdugo City Jan 2 · Dec 26
Frequently asked questions
When is the last frost in Altadena, CA?
The median last spring frost in Altadena, CA is January 8. There is still about a 10% chance of frost after February 17, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Altadena, CA?
The median first fall frost is January 7, with about a 10% chance of frost before December 20.
How long is the growing season in Altadena, CA?
About 364 days between the median last spring frost and first fall frost.
What planting zone is Altadena, CA?
Altadena, CA is in USDA hardiness zone 10b.