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Plant hardiness zones updated

Horticulturist says growers should not be greatly impacted by the update because they have been experiencing conditions for a while.

December 13, 2023

3 Min Read
Tomatoes on vines growing on a wired fence
HARDINESS UPDATE: USDA’s updated Plant Hardiness Zone Map reflects low annual winter temperatures, but gardeners and other growers statewide should not notice big changes in next year’s gardens. William Reagan/Getty Images

by Lauren Wangsness

USDA has unveiled an updated version of its Plant Hardiness Zone Map, an important tool for gardeners and researchers, marking the first update since 2012. The 2023 map offers 13 plant hardiness zones across the United States based on low annual winter temperatures to guide the estimated 80 million American gardeners and growers who are frequent users of the map.

Madeline Wimmer, a University of Minnesota Extension educator based in Rochester, provides insight and stresses the importance of understanding the updates made to the growing map. Wimmer specializes in horticultural science and works with growers around Minnesota.

Wimmer first notes that plants are impacted in a variety of ways by temperature. “Woody plants go through acclimation in the fall. They prepare to go dormant for the wintertime, so they take time to acclimate,” Wimmer says. “What you do not want is, for example, if you are growing fruit trees that flower earlier, the flowers are very sensitive to cold. You do not want something to warm up to the point of breaking bud too early. Once you start getting shoot growth or flowers that are developing and coming out, that is when you are more sensitive to spring frost.”

Wimmer explains that growers should not be greatly impacted by the updates because maps are based on 30-year temperature averages. The conditions “have been the way they have been and can feel very new, but growers have been experiencing the conditions for a while,” she says.

Impact also depends on if a grower experiences a zone change. “If you were in Zone 3b and now you are in Zone 4a, you are not taking huge leaps. You can try something out in your region and maybe it survives for a few years, and then you get one really cold event, and it is gone,” Wimmer says.

She also notes that growers do not immediately need to change any growing habits. “If the maps were going in reverse, I would be more adamant to make sure that people recognize that if winter temperatures were getting colder, they would have less survivability of plants,” she explains. Wimmer assures that slight changes in zones are not alarming for growers because many plants can thrive among a range of zones. She notes that nurseries should be well educated regarding how successful a plant variety will perform in a zone.

Try something new

Wimmer cites the importance of considering other factors impacted by zone changes that can influence growing success. “For example, invasive species pests are also being affected by this. With a pest like emerald ash borer, we have been seeing it more in regions where we did not think it existed,” she says.

Growers face some opportunities in the wake of the updated maps, such as “extended growing seasons that could allow growers to have enough time in the season for their fruit to ripen more fully,” Wimmer says.

Wimmer recommends growers to not shy away from experimenting with plants they have not tried before. “Just recognize that there are still more risk factors that can eventually lead to some sort of problem,” she says.

Most importantly, Wimmer thinks it is necessary that people have an improved understanding of their growing regions. “It is always important for people to be interested in understanding the world around them and be able to recognize that there are many factors that play into the survivability of plants,” she concludes.

New Plant Hardiness Zone Maps are available online through the USDA.

Wangsness writes from St. Paul, Minn.

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