Ontario, CA 91761 Frost Dates
When can you plant in Ontario, CA?
Typically, the last spring freeze lands around 01/04, roughly 129 days out. The first fall frost typically arrives around 12/30, about 365 frost-free days later.
Zone 10a (30 to 35°F average annual minimum) comes from the USDA Plant Hardiness Zone Map; the frost dates above are the 1991-2020 normal at the nearest reporting NOAA station for Ontario, not a forecast for this year.
What to do before the first frost
About 18 weeks of growing season left in Ontario before the first fall frost — a cold frame or row cover can stretch harvest weeks past that date.
The actual range around Ontario's last frost
01/04 is the middle of 30 years of NOAA records, not a promise. Plant by 02/07 and you're betting against frost in roughly 9 years out of 10. 12/14 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Ontario compares
About 365 days separate Ontario's last and first frost, putting it 373 of 40,283 ZIP codes nationally. Within CA, it ranks 128 of 2,555.
Learn more
the frost range covers how to read the range around Ontario's dates instead of trusting one. local microclimates covers what one yard in Ontario can differ from the 91761 normal.