Portola Valley, CA 94074 Frost Dates
94074, near Portola Valley, CA: the frost window
Around 03/02 is the usual last spring frost, about 186 days away. Fall's first freeze usually shows up around 11/25, roughly 268 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Portola Valley in Zone 9b (25 to 30°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
Stretching the season past the first frost
Portola Valley's growing season runs out in roughly 13 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
Why 03/02 isn't a guarantee
03/02 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/15 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 12/31 and only about 1 year in 10 sees frost after that.
Portola Valley against the rest of the dataset
About 268 days separate Portola Valley's last and first frost, putting it 5,765 of 40,283 ZIP codes nationally. Within CA, it ranks 1,989 of 2,555.
Learn more
Two guides worth reading on 94074: zone vs. frost date, on why Zone 9b and Portola Valley's frost date answer different questions, and the frost range, on how to read the range around Portola Valley's dates instead of trusting one.