Denison, IA 51442 Frost Dates
Frost dates for Denison, IA, ZIP 51442
Typically, the last spring freeze lands around 04/27, roughly 242 days out. The first fall frost typically arrives around 10/11, about 166 frost-free days later.
The USDA Plant Hardiness Zone Map puts Denison in Zone 5a (-20 to -15°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 5a around Denison has about 6 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.
Why 04/27 isn't a guarantee
04/27 is the middle of 30 years of NOAA records, not a promise. Plant by 04/13 and you're betting against frost in roughly 9 years out of 10. 05/09 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Denison compares
About 166 days separate Denison's last and first frost, putting it 30,351 of 40,283 ZIP codes nationally. Within IA, it ranks 450 of 1,042.
Learn more
local microclimates explains what one yard in Denison can differ from the 51442 normal, and zone vs. frost date explains why Zone 5a and Denison's frost date answer different questions.