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What the new USDA plant hardiness map means for the Tri-State

close up of a map of ohio, kentucky and indiana in shades of green and yellow with the hardiness scale on the side
New hardiness zones mean gardeners and growers amy need to re-think their planting plans.

When it comes to gardening and growing, there's a map that is the gold standard for determining what plants are most likely to grow successfully in a given location. It's the U.S. Department of Agriculture's Plant Hardiness Zone Map, and it's just been updated to reflect our warming climate.

"Why this is so important (here) is because we can start growing plants that we maybe only just dreamt of growing in the past — and that's a wide range of plants," says Joe Boggs, an assistant professor of Entomology with the Ohio State University Extension in Hamilton County. He's particularly excited about crepe myrtles.

This is the first time the map has been updated since 2012. The 2023 map is 2.5 degrees Fahrenheit warmer than the 2012 map. It's based on 30-year averages of the lowest annual winter temperatures in specific locations.

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Boggs notes you can toggle between the 2012 and 2023 maps on the USDA's website.

"There are dramatic changes," he says.

There are 13 zones, each divided into A and B half zones. The lower the zone number, the colder the overall temperatures.

"Ohio in 2012 was mainly in the 6s. Our area of the country was mainly in what would be called 6a," Boggs says. "The new map has our area in 6b, and the 6as shoved north.

"You look at Kentucky as a state, for example, and the 7s are creeping up. Again, when you look at the two maps, it's a dramatic shift, showing what we know has been happening for quite some time — that the southern environmental conditions are creeping north, and this map very well displays it."

Boggs says the change means we'll be able to grow some plants across the Tri-State that wouldn't have thrived previously, but we aren't far enough north to rule out some plants that need cooler temperatures.

The USDA estimates some 80 million American gardeners and growers use the map most frequently. However, it's also used by the USDA Risk Management Agency to set certain crop insurance standards, and by scientists studying, for example, the spread of invasive weeds, plants and insects.

"This does mean that we'll probably start seeing some of the more southern insects that can't overwinter here creeping further north," Boggs explains. "We don't have a good handle on that yet so I don't want to go too far with that, but it is just something as a cautionary statement that as our climate is changing — and it's made most evident by this change in the map — then we'll start seeing things that are changing relative to all of those things, both plants and animals, that we tend to think of as being more southern."

The change is bad news for people trying to avoid bugs like ticks, but it could be good for some pollinators. Boggs suggests we could start to see some pollinators we've previously not had a lot of.

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"We're actually gaining more plants and we're gaining more insects — greater diversity in this transition zone — but on the other hand, what about those insects and pollinators that require an extensive length of time being cold? Well, that could affect those as well. It could cause some to perhaps suffer more heat degradation, their populations aren't able to make it like they did in the past. But at the end of the day, it does translate into things are going to become a little different. We're going to start seeing some differences."

As NPR reports, about half the country has shifted into a new half zone.

"The scientific community overwhelmingly agrees that humans burning fossil fuels like oil, coal and gas is the primary driver of global warming. The summer of 2023 was the hottest meteorological summer on record for the northern hemisphere, according to the National Oceanic and Atmospheric Administration," NPR states.

Senior Editor and reporter at WVXU with more than 20 years experience in public radio; formerly news and public affairs producer with WMUB. Would really like to meet your dog.