Last frost date in Ontario, CA
The average last frost in Ontario is January 4. By February 7 the chance of another 32°F night drops to 1 in 10. The first fall frost usually arrives about December 30, which leaves 365 frost-free days. An early freeze before December 11 happens one year in ten.
- Safe after (10% risk)
- Feb 7
- Average first frost
- Dec 30
- Frost-free season
- 365 days
- Hard freeze (28°F) ends
- rare
No frost in the next 6 nights
National Weather Service forecast, updated Oct 22, 12:57 UTC
- ThuOct 2255°
- FriOct 2353°
- SatOct 2455°
- SunOct 2557°
- MonOct 2657°
- TueOct 2757°
Planting calendar for Ontario
Windows count forward or back from the average frost dates above. Click a crop for dates across California.
TomatoesFeb 15–Mar 1
PumpkinsFeb 15–Mar 1
SunflowersFeb 15–Mar 8
CucumbersFeb 22–Mar 1
CornFeb 15–Mar 1
Sweet potatoesFeb 15–Mar 1
WatermelonFeb 15–Mar 1
Green beansFeb 15–Mar 8
ZucchiniFeb 15–Mar 1
OkraFeb 15–Mar 1
PeppersFeb 15–Mar 1
BasilFeb 15–Mar 1
Butternut squashFeb 15–Mar 1
CantaloupeFeb 15–Mar 1
EggplantFeb 15–Mar 1
PotatoesDec 7–Dec 21
OnionsNov 23–Dec 14
CarrotsDec 14–Jan 18
LettuceDec 21–Jan 11
BroccoliDec 7–Dec 21
BeetsDec 7–Jan 18
PeasNov 23–Dec 7
CabbageDec 7–Dec 21
RadishesNov 30–Jan 11
Brussels sproutsDec 21–Jan 4
SpinachNov 23–Dec 14
CilantroDec 21–Jan 11
KaleDec 7–Dec 21
Collard greensDec 7–Dec 21
TurnipsDec 7–Dec 21
DillJan 4–Jan 18
CeleryJan 11–Jan 18
CauliflowerDec 21–Jan 4
LeeksDec 21–Jan 4
Swiss chardDec 21–Jan 18
ParsleyDec 21–Jan 11
Tulip bulbsDec 15–Jan 15
GarlicOct 15–Nov 30
Daffodil bulbsOct 15–Nov 30
StrawberriesDec 7–Dec 21
AsparagusDec 7–Dec 21Frost probabilities
| Threshold | Spring, 90% chance later | Spring, 50% | Spring, 10% | Fall, 10% chance earlier | Fall, 50% | Fall, 90% |
|---|---|---|---|---|---|---|
| Light frost, 32°F | Dec 14 | Jan 4 | Feb 7 | Dec 11 | Dec 30 | Feb 1 |
Read the spring 10% column as the date after which only one year in ten still gets frost. That is the safer date for tomatoes, peppers and basil.
Where these numbers come from
NOAA station Ontario International Airport (USW00003102) sits 1.4 miles from the center of Ontario at 949 feet. Its averages cover 1991 to 2020. Low spots, valleys and open fields can keep getting frost a week or two after the station stops; city centers and lakeshores usually get less of it.
Questions
When is the last frost in Ontario, CA?
The average last frost date in Ontario is January 4, based on NOAA 1991–2020 climate normals. There is a 10% chance of frost after February 7.
When is the first frost in Ontario?
The first frost in fall usually comes around December 30. One year in ten it arrives before December 11.
How long is the growing season in Ontario?
About 365 days between the average last and first frost.
When should I plant tomatoes in Ontario?
Plant tomato seedlings outside from February 15 to March 1. Start seeds indoors six to eight weeks earlier.
Nearby in California
- EastvaleJan 17
- ChinoJan 17
- MontclairJan 8
- UplandJan 4
- Rancho CucamongaJan 4
- Jurupa ValleyJan 9
- NorcoJan 17
- ClaremontJan 8
- PomonaJan 8
- Chino HillsJan 17
- FontanaJan 4
- La VerneJan 8