New hardiness zone map will help US gardeners keep pace with climate change

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The recently updated U.S. Department of Agriculture’s “plant hardiness zone map” heralds a significant development for American gardeners, marking the first update in a decade. This revised map carries profound implications for gardening enthusiasts nationwide, shedding light on the evolving landscape of gardens and yards in the context of climate change.

Climate change impacts vary across regions, with the Midwest experiencing more significant warming compared to the Southeast. However, this updated map serves as a valuable compass for growers, offering guidance on which plants, be they flowers, vegetables, or shrubs, are best suited to flourish in specific locales.

A pivotal metric featured on the map is the lowest anticipated winter temperature for a given region, a critical factor in assessing plant survival during the season. This figure is determined by averaging the lowest winter temperatures observed over the past three decades.

Across the contiguous 48 states, the lowest anticipated winter temperature now stands at 2.5 degrees Fahrenheit (1.4 degrees Celsius) higher than it was when the previous map was published in 2012. Chris Daly, a researcher at Oregon State University’s PRISM Climate Group, which collaborates with the USDA’s Agricultural Research Service in producing the map, underscores this notable shift.

Richard Primack, a plant ecologist at Boston University who was not directly involved in the map project, emphasizes that approximately half of the United States has transitioned to a slightly warmer climatic zone in the past decade. This transformation is a striking revelation. Primack cites personal observations, noting that fig trees are now thriving in his garden without the extensive winter protection measures previously required. Additionally, he has observed camellias and southern magnolia trees surviving recent winters in Boston without frost damage, plants typically associated with milder, southern climates.

Primack underscores the accelerated rate of change in winter temperatures and nighttime temperatures, outpacing the overall rise in U.S. temperatures. This shift poses challenges for both plants and cultivators, as adapting to such changes becomes increasingly complex.

However, it’s important to note that warmer winter temperatures come with drawbacks. Theresa Crimmins, a climate change and growing seasons expert at the University of Arizona not involved in the map’s creation, highlights the consequences. Milder winters result in reduced die-backs of disease-carrying insects like ticks and mosquitoes, which can have adverse effects on ecosystems. Moreover, in some regions, hotter and drier summers may threaten the survival of plants that were once well-suited to those environments.

In conclusion, this updated hardiness zone map serves as an invaluable tool for gardeners navigating the shifting landscape of climate change. It provides essential guidance for selecting plant species that are best adapted to the evolving conditions in different regions. As gardeners and growers grapple with these changes, they must remain attentive to the unique challenges and opportunities that accompany a warming world.

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More about Climate Change Gardening

• USDA Plant Hardiness Zone Map
• PRISM Climate Group at Oregon State University
• Boston University – Department of Biology
• University of Arizona – School of Natural Resources and the Environment
• Climate Change and Growing Seasons Research