Climate change is causing a surprising disruption in plant hardiness across the United States. According to the U.S. Department of Agriculture’s plant hardiness zone map, regions that were once too cold for Southern staples like magnolia trees and camellias are now becoming viable environments for their growth.
Updated for the first time in a decade, the USDA’s map reflects the impact of climate change on gardens and yards. It shows that the Midwest has experienced more warming than the Southeast, providing growers with new guidance on which flowers, vegetables, and shrubs are best suited to their specific region.
One particularly significant factor on the map is the lowest likely winter temperature in a given region, which plays a crucial role in determining plant survival during the winter season. This temperature is calculated by averaging the lowest winter temperatures over the past 30 years.
According to Chris Daly, a researcher at Oregon State University’s PRISM Climate Group, the lowest likely winter temperature across the lower 48 states has increased by 2.5 degrees (1.4 degrees Celsius) since the last map was published in 2012.
Richard Primack, a plant ecologist at Boston University, expressed astonishment at the shift in climatic zones, noting that “half the U.S. has shifted to a slightly warmer climatic zone than it was 10 years ago.” He also observed changes in his own garden, such as the survival of fig trees and the flourishing of camellias and southern magnolia trees, traditionally associated with warmer southern climates.
As winter temperatures and nighttime temperatures rise faster than daytime and summer temperatures, the implications for plant survival can be challenging to navigate. Theresa Crimmins, a climate change and growing seasons expert at the University of Arizona, pointed out the downsides of warmer winters, including less severe die-backs of disease-carrying insects like ticks and mosquitoes, and the potential loss of plants due to hotter, drier summers.
As the climate shifts, it becomes increasingly crucial for growers to adapt by selecting plants that are suited to their evolving environment.
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