An updated USDA Plant Hardiness map was released in November 2023. It is the standard by which gardeners and growers can determine which perennial plants are most likely to survive in their location. This map puts the City of Charlevoix and Charlevoix Township in Zone 6a. On the 2012 USDA Map Charlevoix was Zone 5b, and in the 1990 version we were Zone 5a. In the new map about half of the country has shifted to a new zone.
Plant hardiness zone designations represent the “average annual extreme minimum temperature” at a given location during a particular time period (30 years, in the case of the new map). The designations do not reflect the coldest it has ever been or ever will be at a specific location, but simply the average lowest winter temperature, and gardeners know that how cold it is during the winter is a crucial factor in the survival of plants.
The 2012 USDA Zone Hardiness Map (above)
The 2023 map incorporates data from 13,412 weather stations compared to the 7,983 that were used for the 2012 map. The latest edition of the USDA Plant Hardiness Zone Map is GIS (Geographic Information System)-based and is specifically designed for the Internet. It enables viewers to examine plant hardiness zones at a much finer scale than 1990 and earlier maps. Simply type your ZIP Code in the box near the top of the map and your zone will be reported. https://planthardiness.ars.usda.gov
When selecting perennials, the Plant Hardiness Zone is not the only thing to consider. A gardener needs to assess their specific conditions – meaning the microclimate(s) in the garden. Microclimates can be created by a number of things such as physical structures (walls, or buildings). Dense surfaces (brick, stone, concrete, etc.) will hold and radiate heat. They can also shelter plants by blocking the wind. Topography and large bodies of water will change the growing climate, as well.
It’s obvious when you look at the USDA map that Lake Michigan has a huge impact on our climate. As you move to the eastern end of Charlevoix County, you may find yourself in Zone 4. Lake Michigan serves to moderate the climate in Charlevoix. We experience cooler temperatures during the spring and early summer and warmer temperatures during the fall and early winter than locations farther from the lake. The lake effect also increases the cloudiness and snowfall during the fall and winter.
Daisies happily growing in the Depot Heritage Garden on Lake Charlevoix
If you live on top of a hill, or deep in a valley, you will find differences between what the USDA Map says and what is actually happening in your location because topography plays a major role. Valleys can have more frost problems because warm air is lighter than cold air. Rainfall, shade, soil types, mulching practices, paved surfaces, fences or dense hedges can also impact your microclimates.
Clever gardeners can manipulate their microclimates to work for them. So, zone maps are not absolute – they are just one of the tools that are useful in plant selection. Another of those tools is the MSU Extension list of statewide frost free dates. This list can help you decide when it’s safe to put flowering annuals and vegetables into your garden. https://www.canr.msu.edu/resources/frost-free-dates
Colorful Zinnia are happy in the Pere Charlevoix Garden on Lake Michigan
The new map is telling us what we already know – the climate is changing. The region has gotten warmer and wetter since 1900, with Michigan seeing average yearly temperature increase by two to three degrees Fahrenheit and average rainfall increase by around five inches. According to GLISA (a Climate Partnership between the University of Michigan and Michigan State University): https://glisa.umich.edu
The frost-free season lengthened by 16 days in the Great Lakes region from 1951-2017, and may extend up to 50 days longer by 2100.
As air temperatures continue to rise and further warm the Great Lakes, areas in lake-effect zones will continue to see increasing lake-effect snowfall as a warmer atmosphere will be able to hold increasing amounts of moisture.
Since 1951, average temperatures have increased by 2.3°F (1.3°C) in the U.S. Great Lakes region.
By 2050, average air temperatures are projected to increase by 3 to 6°F (1.7 to 3.3°C).
Winter temperatures have been rising faster than temperatures during other seasons.
Some of this may be good news in the short term – warmer weather and fewer frost-free days will give us a longer growing season and widen the selection of plants we can grow. The bad news is that the negative effects of increasing storm activity, flooding, extreme heat, summer drought risks, and pests may outweigh the benefits of warmer temperatures. Researchers at the USDA have been studying the effects of the warming climate on plants. You can read more here: https://www.ars.usda.gov/oc/dof/growing-plants-in-a-hotter-world/
Bergamot is a pollinator-attracting native perennial
The bottom line for us gardeners is the same as it has always been. In order for a plant to thrive we need to choose the right plant for the right place. Yes, we may be able to add azaleas to our gardens now, but they may not survive if all of the other conditions (soil, light, moisture) and the microclimate of the planting location are not right. Native plants are always a good choice for your garden. According to the Xerces Society:
Native, pollinator-attracting plants in the garden
“By greening and transforming our landscapes, we can absorb carbon, reduce urban temperatures, provide habitat that supports pollinators and many other animals, create connections between larger patches of habitat that will allow pollinators to move through our communities—and native plants are the best way to do this. In addition to supporting a greater diversity and abundance of bees, and vastly more species of butterfly and moth caterpillars, native plants are typically better adapted to local conditions, making them easier to grow and more likely to survive.”
For the Xerces Society plant list for the Great Lakes region go to:
https://xerces.org/publications/plant-lists/native-plants-for-pollinators-and-beneficial-insects-great-lakes
or go to the plant list and list of resources in our previous blog post that discusses the benefits of using native plants in your garden: