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USDA updates plant hardiness map for the first time in more than a decade


The U.S. government has updated its map of plant hardiness zones for the first time in more than a decade. The map sets out the average annual extreme minimum winter temperature across the country, and that helps gardeners and growers figure out which plants are most likely to survive the winter. And those averages have changed quite a bit with our warming climate. We were thinking about what this means to a gardener, so we called Ashlie Thomas. She is, as you might expect, a gardener, and she's the author of "How To Become A Gardener." And she's with us now. Ashlie, thanks so much for joining us.

ASHLIE THOMAS: Thank you so much for having me.

MARTIN: Do you consult the plant hardiness map, or how do people use it?

THOMAS: Absolutely. As a gardener, we use it religiously to not just understand what our planting schedules consists of, but also, you know, gauging what is best for us to grow from season to season.

MARTIN: What do you make of the changes of the map? I have to tell you, it was pretty stunning, you know, clicking back-and-forth between 2012 and, you know...


MARTIN: ...2023. It was pretty striking to see the zones kind of moving up - like, the areas where it gets really, really cold shrinking and the areas that get warmer expanding. Has this been changing what you've been planting over the years? Like, how have you noticed it?

THOMAS: So here in North Carolina, we're witnessing that - at the end of November, and we're still hitting some 75-degree weather, you know, during the daytime. And that's something for us to be mindful of because it allows us to see that we have - probably we're going to be going into a longer growing season for those warmer plants. I'm probably not going to chance it this year, but it's definitely something for us to kind of monitor and experiment and explore over the coming years.

MARTIN: What about the extreme heat? I know that there are parts of the world, frankly, that are experiencing heat at temperatures that they just have not seen before and aren't really ready for. And I wonder, what about that?

THOMAS: Yeah. One thing that we found is that the water evaporates faster. So we're starting to think about water conservation. How are we going to maintain a steady water supply for a longer duration of time? Typically, during the fall and the winter months we don't have to water as much. But as the temperatures are increasing, we're starting to see greater evaporation of the water, and we know that that affects soil health. That also affects the way these plants are able to grow. And I will also mention that with the increase in the temperatures, we also have the mosquitoes. I don't know about you, but mosquitoes are awful (laughter). I was - I...

MARTIN: No judgment.

THOMAS: ...Don't like them (laughter).

MARTIN: No judgment.

THOMAS: I don't. Yeah.

MARTIN: So, you know, you were saying that a lot of the gardeners...


MARTIN: ...You know, once this map came out, have been, like, madly googling it. And why is that? Is it - are people kind of in a panic about it, or why is that?

THOMAS: I would hope that it's a range of emotion besides just panic. As we are becoming aware of this climate change that is happening and reflective of our hardiness zones, we also have to be mindful of the behaviors that we take as humans to maybe exacerbating these changes or accelerating these changes over time. So I like to reassure people that as gardeners, we have to be resilient, resilient like the plants - right? - and learn to adjust with the ebbs and flows that's happening in our environment.

MARTIN: Ashlie Thomas is the author of "How To Become A Gardener," and you can also find her online. You can check out her Instagram as @the.mocha.gardener. Ashlie Thomas, thanks so much for talking to us.

THOMAS: Thank you.


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