Frost dates for 91764 — Ontario, 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 Ontario compares
- In a typical year, frost nights in Ontario 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.
- Ontario shares its weather station with Rancho Cucamonga, 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 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
Ontario, 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, 3 km away (elevation 948 ft (289 m)).
ZIP codes in Ontario: 91758 91761 91762 91764
Frost dates near Ontario
- Guasti Jan 4 · Dec 30
- Upland Jan 4 · Dec 30
- Montclair Jan 8 · Dec 28
- Rancho Cucamonga Jan 4 · Dec 30
- Claremont Jan 8 · Dec 28
- Chino Jan 17 · Dec 19
- Pomona Jan 8 · Dec 28
- Mira Loma Jan 9 · Dec 30
Frequently asked questions
When is the last frost in Ontario, CA?
The median last spring frost in Ontario, 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 Ontario, 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 Ontario, CA?
About 360 days between the median last spring frost and first fall frost.
What planting zone is Ontario, CA?
Ontario, CA is in USDA hardiness zone 10a.