Mill Valley, CA 94120 Frost Dates
Frost dates for Mill Valley, CA, ZIP 94120
Typically, the last spring freeze lands around 12/30, roughly 124 days out. The first fall frost typically arrives around 12/25, about 365 frost-free days later.
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.
What to do before the first frost
Zone 10b around Mill Valley has about 17 weeks left before the first fall frost — that's the usual window to get a cold frame up if you want to keep harvesting past it.
How much risk comes with planting early here
12/30 is the middle of 30 years of NOAA records, not a promise. Plant by 03/13 and you're betting against frost in roughly 9 years out of 10. 12/02 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Mill Valley compares
Mill Valley's growing season runs about 365 days, ranking 1,651 of 40,283 US ZIP codes measured here, longest to shortest. Within CA, it ranks 796 of 2,555.
Learn more
the frost range explains how to read the range around Mill Valley's dates instead of trusting one, and local microclimates explains what one yard in Mill Valley can differ from the 94120 normal.