Ottawa, IL 61350 Frost Dates
When can you plant in Ottawa, IL?
Typically, the last spring freeze lands around 04/20, roughly 235 days out. The first fall frost typically arrives around 10/22, about 183 frost-free days later.
The USDA Plant Hardiness Zone Map puts Ottawa in Zone 5b (-15 to -10°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
About 8 weeks of growing season left in Ottawa before the first fall frost — a cold frame or row cover can stretch harvest weeks past that date.
The actual range around Ottawa's last frost
04/20 is the middle of 30 years of NOAA records, not a promise. Plant by 04/06 and you're betting against frost in roughly 9 years out of 10. 05/05 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Ottawa compares
Ottawa's growing season runs about 183 days, ranking 23,779 of 40,283 US ZIP codes measured here, longest to shortest. Within IL, it ranks 877 of 1,548.
Learn more
zone vs. frost date covers why Zone 5b and Ottawa's frost date answer different questions. the frost range covers how to read the range around Ottawa's dates instead of trusting one.