Rock City, IL 61070 Frost Dates
Frost dates for Rock City, IL, ZIP 61070
Around 04/26 is the usual last spring frost, about 241 days away. The first fall frost typically arrives around 10/13, about 169 frost-free days later.
The USDA Plant Hardiness Zone Map puts Rock City 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 Rock City has about 7 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 04/26 isn't a guarantee
04/26 is the middle of 30 years of NOAA records, not a promise. Plant by 04/11 and you're betting against frost in roughly 9 years out of 10. 05/11 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Rock City compares
Rock City's growing season runs about 169 days, ranking 29,593 of 40,283 US ZIP codes measured here, longest to shortest. Within IL, it ranks 1,438 of 1,548.
Learn more
the frost range explains how to read the range around Rock City's dates instead of trusting one, and local microclimates explains what one yard in Rock City can differ from the 61070 normal.