Wisconsin's USDA plant hardiness zones range from 3b to 6a as of the most recent 2023 map update. This is an expansion from earlier maps that showed zones 3 through 5, with zone 6a being a new addition to the state. Zone 6a (-5°F to -10°F) is found along the western shore of Lake Michigan, stretching from Racine County to Sheboygan County and including parts of Door County. The coldest zones, like 3b (-35°F to -30°F), have shrunk significantly and now only cover small areas in northern counties such as Douglas, Washburn, and Sawyer. The majority of Wisconsin falls within zones 4a to 5b, with zone 5b (-15°F to -10°F) expanding westward to include areas like Madison and around Lake Winnebago
. These zones reflect the average annual extreme minimum winter temperatures and are important for gardeners and growers to determine which plants are best suited to survive Wisconsin winters. The shift toward warmer zones is attributed to climate warming and improved data accuracy from more weather stations
. In summary, Wisconsin's planting zones are:
- Zone 3b: Small patches in northern counties (-35°F to -30°F)
- Zone 4a and 4b: Cover much of northern and central Wisconsin (-30°F to -20°F)
- Zone 5a and 5b: Cover southern and some central parts (-20°F to -10°F)
- Zone 6a: New warmest zone along Lake Michigan coast (-10°F to -5°F)
This range helps gardeners select plants that can thrive in their specific local climate conditions within Wisconsin.
