Grantsburg, WI 54840 Frost Dates
Frost dates for Grantsburg, WI, ZIP 54840
Around 05/11 is the usual last spring frost, about 256 days away. The first fall frost typically arrives around 10/01, about 141 frost-free days later.
The USDA Plant Hardiness Zone Map puts Grantsburg in Zone 4a (-30 to -25°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 4a around Grantsburg 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.
The actual range around Grantsburg's last frost
05/11 is the middle of 30 years of NOAA records, not a promise. Plant by 04/27 and you're betting against frost in roughly 9 years out of 10. 05/28 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Grantsburg compares
Grantsburg's growing season runs about 141 days, ranking 36,922 of 40,283 US ZIP codes measured here, longest to shortest. Within WI, it ranks 706 of 860.
Learn more
zone vs. frost date explains why Zone 4a and Grantsburg's frost date answer different questions, and the frost range explains how to read the range around Grantsburg's dates instead of trusting one.