Anybody who loves gardening—including me, although I’m not very good at it—knows the importance of local growing conditions. Sunlight, temperature, rainfall and soil type all help determine whether a plant will thrive or not.
So, last November’s release of the U.S. Department of Agriculture’s (USDA) new hardiness zone map is a big deal. This is the first update of the map since 2012, and the differences are significant.
“Overall, the 2023 map is about 2.5 degrees warmer than the 2012 map across the conterminous United States,” said Christopher Daly, director of the PRISM Climate Group at Oregon State University in a statement. The group worked with the USDA to create the new map.
“This translated into about half the country shifting to a warmer five-degree half zone, and half remaining in the same half zone,” Daly added.
Since the scientific evidence for climate change is usually based on trends in overall average temperatures ranging over 50–100 years, the new map should not be used alone as confirmation of climate change. But it is an indicator that the world is warming.
The map is designed to help gardeners and farmers understand a plant’s hardiness, or its ability to survive the winter at a particular location, or zone. One of the major factors in creating the map is tracking the lowest winter temperatures at a given region. The designations do not reflect a location’s coldest temperatures, but rather the average lowest winter temperature over a specific time.
Those temperatures are calculated on a 30-year average at specific locations. The 2012 map used weather data from 1974 to 2005. The new map was created from data gathered from 1991 to 2020; it incorporates data from 13,412 weather stations across the United States, an increase of more than 5,000 weather stations from the earlier map.
As with the 2012 map, the new version has 13 zones across the United States. Not sure what your zone is? Simply search for your zip code on the USDA’s online map. The USDA’s website also has tips on how to use the map here.
While the zones in North Carolina are warmer than in the previous map, it doesn’t mean you need to rethink your entire garden.
“Microclimates in the landscape still play a critical factor, with hardscapes and other landscape elements providing protection or topography dips causing temperature sinks allowing for more of a cooling effect,” said Luke Owen in a story for the NC Cooperative Extension Service. Owen is an Agriculture Extension Agent in the Buncombe County Center.
“Microclimates can slightly change what hardiness zone classification your plants might be in by offering additional protection or by taking some away,” Owen adds.
This means you can be a bit more adventurous in your planting. Plants that used to be unsuitable for our area might perform better now thanks to warmer weather patterns and climate. If you’ve been thinking about trying a warmer weather plant in the garden but weren’t sure if it would survive, give it a try!
