What the New USDA Gardening Zones Mean for the Midwest

James D’Onofrio wasn’t surprised when the USDA Plant Hardiness Zone Map—just updated for the first time since 2012—shifted his home city of Cincinnati to a warmer zone, a change reflected across much of the country. 

“The map just confirmed everything that I already knew—I’m a solid 6b,” says D’Onofrio. At his suburban home, previously in the cooler Zone 6a, he grows needle and dwarf palmetto palms and posts growing tips on his Cincy Tropics YouTube channel. He’s one of a group of enthusiasts called zone pushers, who like to test the limits of what can survive in their zones. (Palm trees in Chicago or crepe myrtle in Detroit? Why not!)

“In the polar vortex of Christmas 2022 with negative 7 temperatures, 50-mile-per-hour winds and a 20-below wind chill, all my unprotected palms and cacti survived,” he says, adding that, ironically, he only lost a supposedly hardy cherry laurel shrub. 

The Plant Hardiness Zone Map is a key tool to help gardeners determine which perennials are most likely to survive the coldest winter temperatures in their areas. The latest map features improved mapping technology and data from 13,412 weather stations, compared with 7,983 for the 2012 map. It looks at the average annual lowest winter temperatures over a 30-year span (1991-2020). 

Of the current map’s 13 U.S. zones, four zones cover the Midwest, ranging from Zone 3 with average annual winter minimums of -40°F to -30°F in northern Minnesota to Zone 7 with minimums of 0 to 10°F  in the southern tip of Missouri. Each zone is also broken into five-degree half zones. 

The 2023 map reveals nearly half of the country has moved to the next warmer half zone, for an average 2.5 degree increase since the 2012 map.  Minneapolis, for instance, moved from a Zone 4a (minimum average of -25°F to -30°F) to a somewhat balmier 4b (minimum average of -20°F to -25°F). Those in new zones may be able to grow new flowers, vegetables and other plants. 

“Keep in mind the USDA zones are based on 30-year averages, so the next dip might not be for another 10 years—or next month,” says Sean Hogan, a horticulturist, plant breeder and amateur climatologist who participated on the map committee for its past two iterations.

“This map is just one tool in the potting shed,” he says. “It still doesn’t take out the intuitive part of how we garden.” 

To that extent, he encourages gardeners to combine the map data with their own observations and experimentation. Many are expected to take this change as an opportunity to experiment with borderline plants.

“Start small with a $15 shrub that you can throw a blanket over” when trying new plants, he says. “When you can get to the point where losing a plant is part of the sport, then the challenge becomes more fun.” 

Scott Beuerlein, horticulturist at the Cincinnati Zoo & Botanical Garden, reinforces the value of local weather knowledge since the maps “don’t account for microclimates, length of cold, sudden drops, sudden warm-ups, early frosts, late ones, variations in humidity, wet soil, dry soil, and whatever else.”

“Not much has really changed for us,” he says. “Our palette of tried-and-true plants for our region is exactly the same, and those who push zones will continue to do so at their peril. But, of course, they will, me included, because it's interesting and fun.”

Fun indeed. Many gardeners, including members of the Zone Pushers Facebook group, like Cincinnati’s D’Onofrio, embrace experimenting with plants and weren’t surprised by the new warmer zones. The group’s 13,000 members grow palm trees, banana plants, passion vines, ferns, elephant ears, and many other plants outside their normal hardiness zones and share their results.

Zone pusher Derek McKay has found surprising success growing broadleaf evergreens like Southern magnolia and American holly at his home garden in Des Moines (Zone 5b). 

“Several people laughed and said the magnolia wouldn’t work, but it’s been here for four years and survived every weather event,” he says. He recommends placing such marginal plants on the more moderate north side of a house. McKay also grows plants like the yellow-flowering prickly pear cactus—technically hardy for the area, "but it's a very unusual choice and it gets people talking."

Is the warming reflected in the new zone map the result of climate change? The USDA is cautious on that point. “Climate changes are usually based on trends in overall annual average temperatures recorded over 50-100 years,” the agency said when announcing the new map. “Because the USDA [zone map] represents 30-year averages of what are essentially extreme weather events (the coldest temperature of the year), changes in zones are not reliable evidence of whether there has been global warming.”

Regardless of the cause of zone changes, gardeners seem eager for more plant variety. Luckily for the Midwest, the industry is offering more cold-hardy versions of warm-weather plants. Seth Reed, sales and marketing manager with Darwin Perennials, says location is key for producing reliably cold-tolerant plants. 

“Most of our breeding is in West Chicago in the heart of the Midwest where the winters are brutal, so gardeners can have confidence knowing their plants will truly endure in other zone 5 areas of the Midwest.” He points to Sombrero coneflowers as an example that outperforms coneflowers bred in other warmer parts of the country.

Proven Winners, another plant breeder with operations in Michigan, recently introduced more cold-hardy hydrangeas and roses including Tuff Stuff Top Fun mountain hydrangea (Zone 4), Pink Winky Prime panicle hydrangea (Zone 3), Oso Easy Ice Bay rose (Zone 3) and Flavorette honey-apricot rose (Zone 4). Bailey Nurseries of St. Paul, Minnesota, recently introduced Iceberg Alley sageleaf willow (Zone 2) and Endless Summer Pop Star hydrangea (Zone 4).

To learn more, check out the interactive map, type in your zip code to find your zone and explore the growing tips.