See Climate Change on the Map: Plant Hardiness Zones Shift North

The United States Department of Agriculture this month produced perhaps the best illustration yet of the reality of climate change. On November 15, the USDA released a new Plant Hardiness Zone Map. The first update since 2012, the new Plant Hardiness Zone Map includes lots more data:

The new map—jointly developed by USDA’s Agricultural Research Service (ARS) and Oregon State University’s (OSU) PRISM Climate Group—is more accurate and contains greater detail than prior versions.

It is available online at https://planthardiness.ars.usda.gov/. In addition to the map updates, the Plant Hardiness Zone Map website was expanded in 2023 to include a “Tips for Growers” section, which provides information about USDA ARS research programs of interest to gardeners and others who grow and breed plants.

The 2023 map is based on 30-year averages of the lowest annual winter temperatures at specific locations, is divided into 10-degree Fahrenheit zones and further divided into 5-degree Fahrenheit half-zones. Like the 2012 map, the 2023 web version offers a Geographic Information System (GIS)-based interactive format and is specifically designed to be user-friendly. Notably, the 2023 map delivers to users several new, significant features and advances. The 2023 map incorporates data from 13,412 weather stations compared to the 7,983 that were used for the 2012 map.

Furthermore, the new map’s rendering for Alaska is now at a much more detailed resolution (down from a 6 ¼ -square-mile area of detail to a ¼ square mile). “These updates reflect our ongoing commitment to ensuring the Plant Hardiness Zone Map remains a premier source of information that gardeners, growers and researchers alike can use, whether they’re located in the continental United States, Alaska, Hawaii or Puerto Rico,” said ARS Administrator Dr. Simon Liu [USDA, press release, 2023.11.15].

NPR smartly puts the new 2023 map on top of the 2012 map so we can flip back and forth see just how the zones have changed.

The changes may not look huge from space—no place jumped from a frigid 4b to a sweltering 12a. No one’s growing corn in Nome yet. But especially in the Great Plains and Midwest, you can see the zones creeping northward by maybe a hundred miles. That’s not a sudden storm or a stray September heat wave; that’s a significant climatic shift over just 11 years affecting what kind of plants can grow where.

Here’s a close-up of South Dakota, North Dakota, and Minnesota:

In 2012, South Dakota was mostly 4a and 4b, with a little bit of 5a in the Black Hills and the Burke–Yankton–Sioux City sunbelt. That 5a sunbelt now reaches up past Sioux Falls, almost to Pierre, and contiguïzed into the Hills to cover the bottom third of the state. Some islands of 5b have popped up into that expanding 5a zone. The frosty 4a has been pushed almost entirely out of northwestern South Dakota and has shrunken to that ingress into the James River Valley and a couple islands in the Prairie Coteau (that north island may correspond to the foggy blizzardy Bermuda Triangle around Summit).

The USDA goes easy on the climate-change angle, but the maps show what gardeners can see in their backyards—we are changing where things can grow:

In an email, a press officer for the USDA says, “Changes to plant hardiness zones are not necessarily reflective of global climate change because of the highly variable nature of the extreme minimum temperature of the year.”

But [director of OSU PRISM Climate Group Chris] Daly says, in the big picture, climate change is playing a role in changing what grows where in the US: “Over the long run, we will expect to see a slow shifting northward of zones as climate change takes hold.”

Still, for gardeners like Rachel Patterson, in Port St. Joe, Florida, the updated USDA map showing a warming region is validating, if not comforting. “It feels like I’m not crazy,” she says [Julia Simon, “‘It Feels Like I’m Not Crazy.’ Gardeners Aren’t Surprised as USDA Updates Key Map,” NPR, 2023.11.17].

Remember: more tomatoes and arugula are great, but only if the hotter planet doesn’t spin up more intense thunderstorms and floods and dust storms that wipe them out.