Frost dates for Ontario, California
In a typical year, Ontario’s last spring frost lands around Jan 4 and the first fall frost around Dec 30, a growing season of about 360 days. These are odds drawn from 30-year NOAA climate normals, not a promise. USDA zone 10a.
Right now the growing season is open, with about 66 days until the typical first fall frost.
| Odds | Last spring frost | First fall frost |
|---|---|---|
| 10 percent | Dec 14 | Dec 11 |
| 50 percent | Jan 4 | Dec 30 |
| 90 percent | Feb 7 | Feb 1 |
A 10 percent year is an early year, a 90 percent year a late one. Frost-sensitive planting usually waits for the 90 percent side of the last-frost band.
Soil in Ontario is typically around 68°F at 4 inches this time of year, estimated from the last two weeks of normal air temperatures.
Plantable now in Ontario
- Beet (Detroit Dark Red)
- Spinach (Space)
- Swiss chard (Bright Lights)
- Kale (Lacinato)
- Dill (Bouquet)
- Chives (Common Chives)
- Calendula (Pacific Beauty)
- Zucchini (Eight Ball)
Timing comes from the same temperature engine the app uses, run against Ontario’s normals for today.
Common questions
When is the last frost in Ontario, California?
Ontario’s last spring frost falls around January 4 in a typical year. One year in ten it is done by December 14, and one year in ten frost holds on until February 7. Frost-sensitive planting usually waits for the late side of that band.
When is the first fall frost in Ontario?
The first fall frost arrives around December 30 in a typical year, as early as December 11 in an early year and as late as February 1 in a late one.
How long is the growing season in Ontario?
About 360 days, counted between the typical last spring frost and the typical first fall frost.
What USDA zone is Ontario in?
Ontario is in USDA hardiness zone 10a under the 2023 USDA Plant Hardiness Zone Map.
Dates come from 30-year NOAA climate normals for the nearest reporting station. They describe odds, not a forecast.
Nearby cities
- Pomona, CA (around Jan 8 to Dec 28)
- Rancho Cucamonga, CA (around Jan 4 to Dec 30)
- Fontana, CA (around Jan 9 to Dec 30)
- Corona, CA (around Jan 17 to Dec 19)
- Riverside, CA (around Jan 9 to Dec 25)
Row & Bed is a plant reference built around your garden: your zone, your frost dates, your forecast, and a cited page for every variety in your beds.
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