Rialto, CA frost dates
Frost is light and occasional here — typically a few cold nights around midwinter (about 2 a year). Cover tender plants when frost is forecast.
How Rialto compares
- In a typical year, frost nights in Rialto fall between January 2 and January 10. In 1 year in 10 the first frost comes as early as December 11, or the last frost as late as February 17.
- Compared with Fontana, CA, 8 km away, the last frost here is 6 days later than there.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | December 20 |
| 50% (median) | January 10 |
| 10% (safe for tender plants) | February 17 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | December 11 |
| 50% (median) | January 2 |
| 90% (late) | February 7 |
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
Rialto, 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 Riverside Citrus Exp, CA weather station, 19 km away (elevation 988 ft (301 m)).
ZIP codes in Rialto: 92376 92377
Frost dates near Rialto
- Bloomington Jan 10 · Jan 2
- Fontana Jan 4 · Dec 30
- San Bernardino Jan 27 · Dec 19
- Grand Terrace Jan 10 · Jan 2
- Cedarpines Park May 5 · Nov 2
- Colton Jan 27 · Dec 19
- Patton Jan 27 · Dec 19
- Loma Linda Jan 27 · Dec 19
- Crestline May 5 · Nov 2
- Highland Jan 27 · Dec 19
Frequently asked questions
When is the last frost in Rialto, CA?
The median last spring frost in Rialto, CA is January 10. 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 Rialto, CA?
The median first fall frost is January 2, with about a 10% chance of frost before December 11.
How long is the growing season in Rialto, CA?
About 357 days between the median last spring frost and first fall frost.
What planting zone is Rialto, CA?
Rialto, CA is in USDA hardiness zone 10a.