Mason, WI 54821 Frost Dates
Frost dates for Mason, WI, ZIP 54821
Typically, the last spring freeze lands around 05/16, roughly 261 days out. The first fall frost typically arrives around 09/30, about 136 frost-free days later.
Zone 4a (-30 to -25°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 Mason, not a forecast for this year.
What to do before the first frost
Zone 4a around Mason has about 5 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
05/16 is the middle of 30 years of NOAA records, not a promise. Plant by 05/01 and you're betting against frost in roughly 9 years out of 10. 05/27 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Mason compares
At roughly 136 frost-free days, Mason places 37,808 of 40,283 ZIP codes in this dataset. Within WI, it ranks 767 of 860.
Learn more
the frost range explains how to read the range around Mason's dates instead of trusting one, and local microclimates explains what one yard in Mason can differ from the 54821 normal.