Mill Valley, CA 94141 Frost Dates
94141, near Mill Valley, CA: the frost window
Typically, the last spring freeze lands around 12/30, roughly 124 days out. Fall's first freeze usually shows up around 12/25, roughly 365 days after the last spring frost.
Zone 10b (35 to 40°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 Mill Valley, not a forecast for this year.
Stretching the season past the first frost
Mill Valley's growing season runs out in roughly 17 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
How much risk comes with planting early here
12/30 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 12/02 and only about 1 year in 10 sees frost after that.
Mill Valley against the rest of the dataset
Mill Valley's growing season runs about 365 days, ranking 1,657 of 40,283 US ZIP codes measured here, longest to shortest. Within CA, it ranks 802 of 2,555.
Learn more
Two guides worth reading on 94141: local microclimates, on what one yard in Mill Valley can differ from the 94141 normal, and zone vs. frost date, on why Zone 10b and Mill Valley's frost date answer different questions.