Ontario, CA 91764 Frost Dates
91764, near Ontario, CA: the frost window
The last spring frost here typically falls around 01/04, about 129 days from today. Fall's first freeze usually shows up around 12/30, roughly 365 days after the last spring frost.
Ontario sits in USDA Zone 10a (30 to 35°F average annual minimum). The dates above are NOAA's 1991-2020 normal at the nearest reporting station, a 30-year average, not a forecast.
Stretching the season past the first frost
Ontario's growing season runs out in roughly 18 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
The actual range around Ontario's last frost
01/04 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 02/07 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 12/14 and only about 1 year in 10 sees frost after that.
Ontario against the rest of the dataset
Ontario's growing season runs about 365 days, ranking 374 of 40,283 US ZIP codes measured here, longest to shortest. Within CA, it ranks 129 of 2,555.
Learn more
Two guides worth reading on 91764: local microclimates, on what one yard in Ontario can differ from the 91764 normal, and zone vs. frost date, on why Zone 10a and Ontario's frost date answer different questions.