Rancho Cucamonga, CA 91739 Frost Dates
91739, near Rancho Cucamonga, CA: the frost window
Around 01/04 is the usual last spring frost, about 129 days away. Fall's first freeze usually shows up around 12/30, roughly 365 days after the last spring frost.
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 Rancho Cucamonga, not a forecast for this year.
Stretching the season past the first frost
Rancho Cucamonga'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 Rancho Cucamonga'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.
Rancho Cucamonga against the rest of the dataset
Rancho Cucamonga's growing season runs about 365 days, ranking 379 of 40,283 US ZIP codes measured here, longest to shortest. Within CA, it ranks 133 of 2,555.
Learn more
Two guides worth reading on 91739: zone vs. frost date, on why Zone 10a and Rancho Cucamonga's frost date answer different questions, and the frost range, on how to read the range around Rancho Cucamonga's dates instead of trusting one.