Diamond Bar, CA frost dates
Frost is light and occasional here — typically a few cold nights around midwinter (about 3 a year). Cover tender plants when frost is forecast.
How Diamond Bar compares
- In a typical year, frost nights in Diamond Bar fall between December 28 and January 8. In 1 year in 10 the first frost comes as early as December 5, or the last frost as late as February 18.
- Diamond Bar shares its weather station with Pomona, CA, 8 km away, so the two have the same frost dates.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | December 14 |
| 50% (median) | January 8 |
| 10% (safe for tender plants) | February 18 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | December 5 |
| 50% (median) | December 28 |
| 90% (late) | February 2 |
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
Diamond Bar, 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 Pomona/Fairplex, CA weather station, 9 km away (elevation 1,001 ft (305 m)).
Frost dates near Diamond Bar
- Walnut Jan 8 · Dec 28
- Pomona Jan 8 · Dec 28
- Chino Hills Jan 17 · Dec 19
- Rowland Heights rare frost
- Brea rare frost
- San Dimas Jan 8 · Dec 28
- West Covina Jan 8 · Dec 28
- Covina Jan 8 · Dec 28
- Montclair Jan 8 · Dec 28
- La Verne Jan 8 · Dec 28
Frequently asked questions
When is the last frost in Diamond Bar, CA?
The median last spring frost in Diamond Bar, CA is January 8. There is still about a 10% chance of frost after February 18, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Diamond Bar, CA?
The median first fall frost is December 28, with about a 10% chance of frost before December 5.
How long is the growing season in Diamond Bar, CA?
About 354 days between the median last spring frost and first fall frost.
What planting zone is Diamond Bar, CA?
Diamond Bar, CA is in USDA hardiness zone 10a.