St. Helena, CA 94573 Frost Dates
94573, near St. Helena, CA: the frost window
Typically, the last spring freeze lands around 02/03, roughly 159 days out. Fall's first freeze usually shows up around 12/04, roughly 306 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts St. Helena 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
St. Helena's growing season runs out in roughly 14 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 St. Helena's last frost
02/03 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 03/13 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 12/28 and only about 1 year in 10 sees frost after that.
St. Helena against the rest of the dataset
About 306 days separate St. Helena's last and first frost, putting it 3,689 of 40,283 ZIP codes nationally. Within CA, it ranks 1,497 of 2,555.
Learn more
Two guides worth reading on 94573: zone vs. frost date, on why Zone 9b and St. Helena's frost date answer different questions, and the frost range, on how to read the range around St. Helena's dates instead of trusting one.