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Some changes to USDA guidance on Plant Hardiness Zones

USDA changes plant hardiness zones due to climate change
Posted at 11:55 AM, Mar 14, 2024

BILLINGS — It's almost planting season in Montana, and it's been extended in Billings because the U. S. Department of Agriculture updated its plant hardiness zone map for the first time in over a decade.

Different areas of the United States have different planting time zones based on the weather, according to the USDA.

“Worldwide, there are zones for growing and it goes by temperature. Here in Billings, Montana, we are warming up a little bit,” said Michael Walz, an association member with the Yellowstone County Master Gardeners Association. “It’s exciting from a standpoint that you might be able to plant certain plants that are from a five-zone, or warmer climate. So, we’re looking at maybe fruit trees, maybe some varied vegetables.”

USDA changes plant hardiness zones due to climate change
2023 map of plant hardiness zones in Montana.

In 2012, Billings was classified as a 4b zone. Now, it is a 5a zone, the next highest classification. The plant hardiness map is the standard that gardeners follow to determine which perennial plants are more likely to thrive in that location. Now in a 5a zone, there is an opportunity for gardeners to try to grow a wider variety of plants.

“The frost-free date here in Billings is usually in June, the first of June, and it ends in October. Well, your frost-free date is now increasing. It used to be 90 days, now it's increasing. Could go up to 95, 100 days,” said the president of the Yellowstone County Master Gardeners, Paul Scarpari.

Scarpari said there are places in Billings that can now try to grow “peaches, cherries or chestnut trees.”

According to the USDA, over half of the country shifted to warmer plant zones, with the lower 48 states all warming by 2.5 degrees in 2023 compared to 2012.

“You know it’s like everything else. There’s a good to it and there’s a bad to it. Which means you’re going to be able to grow crops here, different crops, but then also that you’re going to have insects. More insects,” Scarpari said.

The USDA does not recommend removing the plants that are always planted in your garden or changing what you usually do. While you can now experiment with new plants this year, the plants that typically thrive for you will continue to do so.