Hoffman Estates is in hardiness zone 5b

What the zone tells you

A hardiness zone answers exactly one question: how cold does it get here in an average winter, at worst. It is calculated from the mean annual extreme minimum — the coldest night of each year, averaged over the record. For Hoffman Estates that figure is -25.3°C (-13.6°F), which places it in zone 5b.

Compare this figure with the cold-hardiness range of the exact cultivar you plan to buy. A compatible rating is a useful first screen, but does not guarantee survival: drainage, exposure, plant age and the duration of cold also matter. Roots in containers may need more protection than roots in the ground. Ask the supplier about local experience with the same cultivar.

What it does not tell you

It says nothing about when to plant. Two places can share a zone and have growing seasons that differ by six weeks, because a zone is a single winter night and a season is the gap between the last frost of spring and the first of autumn. A maritime climate and a continental one can sit in the same zone and behave nothing alike.

In Hoffman Estates that gap runs to about 179 frost-free days on a median year, with the last spring frost around 26 April. Those are the numbers that decide a sowing date, and they are what the planting calendar is built on.

It also says nothing about heat, drought, humidity or the length of your summer, all of which can matter more than winter cold. A zone number is a floor, not a description of a climate.