Mill Valley, CA 94151 Frost Dates
Frost dates for Mill Valley, CA, ZIP 94151
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.
The USDA Plant Hardiness Zone Map puts Mill Valley in Zone 10b (35 to 40°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
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.
The actual range around Mill Valley's last frost
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
At roughly 365 frost-free days, Mill Valley places 1,663 of 40,283 ZIP codes in this dataset. Within CA, it ranks 808 of 2,555.
Learn more
local microclimates explains what one yard in Mill Valley can differ from the 94151 normal, and zone vs. frost date explains why Zone 10b and Mill Valley's frost date answer different questions.