The USDA Plant Hardiness Zone Map is the standard by which gardeners and growers can determine which perennial plants are most likely to thrive at a location. 

Recently updated, the map is based on the average annual extreme minimum winter temperature. U of I Extension Program Coordinator Sarah Ruth says the last map from 2012 was updated to reflect data in 2023.

She says the zones do not offer hard and fast boundaries, but rather gray areas in which zones can vary in temperature from one town to the next.