Lanark, IL 61046 Frost Dates
61046, near Lanark, IL: the frost window
Around 05/02 is the usual last spring frost, about 247 days away. Fall's first freeze usually shows up around 10/07, roughly 154 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Lanark in Zone 5a (-20 to -15°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
Stretching the season past the first frost
Lanark's growing season runs out in roughly 6 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
Why 05/02 isn't a guarantee
05/02 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/18 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/18 and only about 1 year in 10 sees frost after that.
Lanark against the rest of the dataset
About 154 days separate Lanark's last and first frost, putting it 34,348 of 40,283 ZIP codes nationally. Within IL, it ranks 1,545 of 1,548.
Learn more
Two guides worth reading on 61046: zone vs. frost date, on why Zone 5a and Lanark's frost date answer different questions, and the frost range, on how to read the range around Lanark's dates instead of trusting one.