The U.S. Department of Agriculture provides gardeners with plant hardiness zones to help them determine what plants will thrive in their climate. Michigan, a large state in the Midwest, reflects several growing zones. Knowing which zone you are in is basic to gardening success, telling you when to plant, when to harvest and how to avoid plant death from climate conditions.
Know Your Zone
Plant hardiness zones in Michigan, based on winter low temperatures, range from Zone 4a, with a minimum of minus 30 degrees Fahrenheit, to Zone 6b, with a low of minus 5 degrees. The range of climate conditions means that plants that grow robustly along the eastern shore of Lake Michigan, which benefits from warmer winters, are likely to die in the cold winters of the Upper Peninsula. You can check the USDA’s zone map to find the specific zone for your part of Michigan. It’s smart to purchase plants grown in the zone in which you live because plants shipped to your state may have been grown in quite different conditions.
Wait, There's More to It
The low winter temperatures reflected in the USDA’s plant hardiness zone map are only one factor in plant health. High temperatures and humidity aren’t measured when assigning zones, but these things affect plant health, too. Sunset magazine and the American Horticultural Society independently developed maps that take high temperatures into account. Sunset divides the country into 45 zones, while the horticultural society assigns 12. Cultural factors, such as soil drainage and mulch, also contribute to plant hardiness.
You can identify microclimates in your yard to stretch your plants’ zone hardiness. A spot that stays sunny in winter and is protected from cold wind by a heat-holding rock wall, building or stout fence may create a warm spot where plants from a higher zone may thrive. Likewise, a slope or low spot in the yard may be a frost pocket, making it a poor place to site a vegetable bed. You can track these spots with an outdoor thermometer.
USDA planting zones are based on average minimum winter temperatures, so temperatures may drop below that figure, killing plants. According to Jeff Andresen, Michigan’s state climatologist, Michigan as a whole is warming up, due to less ice forming on Lake Michigan in the winter, which mitigates winter temperatures. The 2012 map of USDA hardiness zones is based on 1976-to-2005 weather data. In general, the zones in the new map, which replaces the 1990 version, are half a zone warmer.
- U.S. Department of Agriculture: Plant Hardiness Zone Map 2012
- The Michigan Gardening Guide; Jerry Minnich
- The Michigan Gardener’s Companion: An Insider’s Guide to Gardening in the Great Lakes State; Rita C. Henehan
- Mlive: A Conversation With Michigan's State Climatologist Jeff Andresen
- U.S. Department of Agriculture: What’s New
- Photo Credit kdow/iStock/Getty Images
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