Starting a Garden: Understanding Zones
In gardening circles when people talk about Zones or ask you what Zone you live in they are asking about the USDA Plant Hardiness Zone Map. Hardiness refers to a plant's ability to tolerate temperatures. In this case we're talking, mostly, about a plant's ability to survive a winter in Chicago and return the next spring. Currently, Chicago is categorized as being Zone 5b where minimum temperatures range from -10 to -15° F.
The back of a plant label will usually indicate a plant's hardiness either in temperature or to a zone. One thing I find a little annoying about the big box garden centers is that they will often sell plants that aren't hardy to our area. A person new to gardening or just looking to spruce up their garden, patio, deck or porch will buy these plants and they have no idea that they will not survive a winter outdoors in Chicago. If the plant you are interested in buying doesn't have a label that clearly states if the plant is hardy to our area and if the staff at the garden center/nursery don't know the answer either--shop somewhere else.
Rumor has it that in the next update of the USDA Plant Hardiness Zone Map Chicago will be bumped to a Zone 6.