Frost dates for 92377 — Rialto, CA
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 December 30 and January 4. In 1 year in 10 the first frost comes as early as December 11, or the last frost as late as February 7.
- Rialto shares its weather station with Fontana, CA, 9 km away, so the two have the same frost dates.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | December 14 |
| 50% (median) | January 4 |
| 10% (safe for tender plants) | February 7 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | December 11 |
| 50% (median) | December 30 |
| 90% (late) | February 1 |
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 Ontario Intl Ap, CA weather station, 21 km away (elevation 948 ft (289 m)).
ZIP codes in Rialto: 92376 92377
Frost dates near Rialto
- Fontana Jan 4 · Dec 30
- Bloomington Jan 10 · Jan 2
- San Bernardino Jan 27 · Dec 19
- Cedarpines Park May 5 · Nov 2
- Crestline May 5 · Nov 2
- Lytle Creek May 16 · Oct 13
- Rancho Cucamonga Jan 4 · Dec 30
- Grand Terrace Jan 10 · Jan 2
Frequently asked questions
When is the last frost in Rialto, CA?
The median last spring frost in Rialto, CA is January 4. There is still about a 10% chance of frost after February 7, 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 December 30, with about a 10% chance of frost before December 11.
How long is the growing season in Rialto, CA?
About 360 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.