I have been using buddleia, a flowering shrub, as a perennial in the garden for the past few years. That was not the case a decade ago, when the plant would have died in Minnesota winters.
Now the U.S. Department of Agriculture has made official what I and countless other gardeners have known for some time: Americans are adapting to warming weather, right in their backyards.
The U.S.D.A. updated its Plant Hardiness Zone Map in November 2023 for the first time in more than a decade, showing that about half the United States has moved into a slightly warmer zone. The map divides the country into color-coded zones, each indicating the average low temperature of the year. The map is based on the 30-year average of the lowest annual winter temperatures for specific places. It is divided into 13 zones, each reflecting a 10-degree temperature range, and each zone is divided into two half zones, designated as A and B. The coldest area, as low as negative 60 degrees F, applies to remote regions of Alaska. The warmest, as high as 70 degrees, covers coastal areas of Puerto Rico.
This is not the first version of the map to show planting zones shifting northward as winters become milder. When the Agriculture Department released a 2012 version of the map, most areas of the country had shifted a half zone from the 1990 version. While the 2023 shift is minor compared with the 2012 map, it still reflects significant changes when examined over a longer period of time.
Gardeners need to know which zone they’re in because winter temperatures will play a major role in determining which plants will survive to spring, which ones should be taken inside, and which ones shouldn’t be planted in the first place. If gardeners want to push their limits on new zones a bit, they should do so in the spring and early summer and give the plant a chance to take root before winter. Just keep on planting!