USDA releases first updated Plant Hardiness Zone Map in over 10 years, representing a 2.5 degrees F increase in temperaturesNov 20, 2023 10:49AM ● By Content Editor
By Laura Durenberger-Grunow - Boreal Community Media - November 17, 2023
If you're a gardener, it's likely you're familiar with the USDA Plant Hardiness Zone Map. If you're not familiar with it, the map is a guide for gardeners to determine which perennials are hardy to a particular area (meaning, which plants are most likely to survive through winter and come back year after year), although some use it more as a textbook than a guide, myself included.
The last time the USDA issued an updated version of the zones was in 2012, so it's not too surprising there are differences. When my family and I were first thinking about moving up to Cook County in 2021, one of the first things I looked at was the Plant Hardiness Zone Map for the area. Yes, seriously. As an avid gardener for the prior few years in a solid "4b" Plant Hardiness Zone that was the Twin Cities, I had started to see plants that were assigned a zone 5 hardiness level come back year after year. Other gardeners in my community were noticing the same, so the updated map wasn't a huge surprise (most of the Twin Cities Metro area is now in a 5a zone). However, the data behind the increase was a little bit more startling.
Chris Daly, Director of the PRISM Climate Group at Oregon State University, an organization that worked with the USDA to develop the map, told NPR News that the new zones indicate a 2.5 degree F increase in temperatures across the continental US. The increases have pushed half the country into a new zone (including a number of areas in Minnesota), Daly said. However, the USDA states that part of the reason for the increase is better technology, as well as the addition of more data points. The other important thing to note is that although 97% of scientists overwhelmingly agree the earth's temperature is increasing, the Zone Hardiness Map is not the most accurate indicator of climate change. This is due to the fact that the temperature data collected represents an average of 30 years of temperatures, whereas, for climate change data, scientists usually look at a 50-100 year average.
2023 Hardiness Zone Map for Cook County, USDA
2012 Plant Hardiness Zone Map for NE Minnesota, USDA
For Cook County residents, the 4a and 4b zones have increased further inland. There are even a couple of very small areas right along the shoreline that are in 5a.
Map of Downtown Grand Marais and surrounding areas from the 2023 USDA Plant Hardiness Zone map, USDA
For some Minnesota gardeners, the change in hardiness zones simply means that there may be new perennials in their future.
For more information on the 2023 USDA Plant Hardiness Zone Map, visit: https://planthardiness.ars.usda.gov/
2023 USDA Plant Hardiness Zone Map