For years, gardeners looking for weather-appropriate items to plant in the Powell area have focused on plants able to be grown in Zone 4, a colder weather growing region.

However, a combination of more data points to examine and some warming temperatures has changed that metric. Now, much of the county is rated as Zone 5, which has a slightly higher average extreme low temperature and thus, more options for weather appropriate plants.

“A lot of landscape and fruit trees are rated for that,” said Park County Extension Horticulturist Ted Smith.

He said while the Powell area has a slightly shorter growing season than in Cody, it’s still enough for a wide variety of plants to be grown.

“You just pretty much got to pick something that fits within your growing season,” Smith said.

The change in zone is thanks to the USDA, which in 2023 released an updated Plant Hardiness Zone Map for the first time since 2012.

USDA’s Plant Hardiness Zone Map is the standard by which gardeners and growers can determine which plants are most likely to thrive at a location. According to a USDA release, 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.

The map shows most of the western Big Horn Basin as being in Zone 5A (the colder of the two Zone 5s) with some smatterings of colder 4B areas and other warmer Zone 5B areas.

Much of Park County, including around Powell and Cody, are squarely in 5A, meaning the average annual extreme minimum temperature for 1992-2020 is minus 15-20 degrees Fahrenheit.

The 2023 map incorporates data from 13,412 weather stations compared to the 7,983 that were used for the 2012 map.

“It might be just as much that it's more accurately reflecting the conditions that there are, rather than changing conditions,” Smith said.

And gardeners in the Powell area happy to have a little more variety are far from alone — when compared to the 2012 map, the 2023 version reveals that about half of the country shifted to the next warmer half zone, and the other half of the country remained in the same half zone, according to the USDA release. That shift to the next warmer half zone means those areas warmed somewhere in the range of 0-5 degrees Fahrenheit; however, some locations experienced warming in the range of 0-5 degrees Fahrenheit without moving to another half zone.

For more information the the hardiness zone map, visit planthardiness.ars.usda.gov.

And for tips on what to plant in your specific area based on other factors such as soil type, contact Smith at ted.smith@parkcounty-wy.gov or 307-527-8560.