Minor changes have been made to the USDA hardiness map

Minor changes have been made to the USDA hardiness map

Late last November, the United States Department of Agriculture (USDA) released an updated map of the U.S. Plant Hardiness Zone. Gardeners use this map to determine which plants and specific types of plants will thrive in the locations where they plant their gardens. This update includes revised maps for each of the 50 states. This is the first time this national map has been updated since 2012.

The new map is based on 30-year averages of the lowest annual winter temperature in a given location. The 2023 map includes data from 13,412 weather stations across the country compared to the 7,983 stations used for the 2012 map.

Changes to the map of Ohio

On the 2012 Plant Hardiness Zone map, Greater Columbus (and much of the rest of Ohio) was located in Zone 6a, where the average minimum temperature ranges from -10 to -5 degrees Fahrenheit. In the 2012 edition of the map, several locations in Ohio were located in Zone 5B, where average minimum temperatures range from -15 to -10 degrees Fahrenheit.

In the revised 2023 map, about half of Ohio is in Zone 6B, where the average low temperature ranges from -5 to 0 degrees Fahrenheit. The other half of Ohio now lies in Zone 6A, where the average low temperature ranges from -10 to -5 degrees Fahrenheit. For the first time, a larger portion of the southern region of Ohio is now in Zone 7A, where the average low temperature ranges from 0 to 5 degrees Fahrenheit. There are no longer locations in Ohio in Zone 5B, where the average low temperature ranges from -15 to -10 degrees Fahrenheit.

Almost all of Franklin and Pickaway counties have moved into warmer Zone 6B, as have most parts of Delaware and Fayette counties, and parts of Fairfield, Madison and Union counties. Licking, Marion, Morrow and Knox counties remain in District 6A. To find your exact zone, go to: planthardiness.ars.usda.gov and click on Ohio on the interactive map of the United States.

Use the map to make decisions about plants

Changes in hardiness zones should not cause gardeners or commercial seed producers and plant growers to change the plants used in our gardens and home landscapes any time soon. Although most sites in Ohio have moved to a warmer zone, these sites have only changed “half a zone,” which is what the letters following the numbered zones indicate. In Greater Columbus, the move from Zone 6a to 6b is only a 5 degree warmer shift. It is important to remember that these areas are based on historical averages, and there is always the possibility of temperatures falling below the average low temperature anywhere.

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Climate change and plant hardiness zones

Although you and I may not need to change the plants we use in our gardens and home landscapes this upcoming season based on the latest changes in the plant hardiness zone map, our grandchildren and great-grandchildren will likely need to plant different plants and different plant varieties than we currently grow in Columbus. major, simply because of the long-term effects of climate change.

Weather is a term that describes high-frequency changes in temperature, wind speed and other conditions caused by anomalies around the world. Climate is the term used to describe the slower changing aspects of weather averages over longer periods of time. Documented long-term climate changes occurring in Ohio include a longer growing season; warmer temperatures (especially in winter and at night); Higher humidity more rain. more intense rainfall events; More rainfall in the fall months. All of these changes will have an impact on which plants will thrive in Ohio in the future.

Long-term models suggest that with the current trajectory of these climate changes, by 2030, summer weather in Ohio could be similar to current summer climate conditions in southwestern Kentucky. The weather during Ohio’s winters will likely be similar to the current winter conditions experienced in southern Virginia.

The same models indicate that by 2095, summer weather in Ohio will be similar to current summer weather conditions seen in Arkansas, with winter weather in Ohio similar to conditions typically experienced in southern North Carolina. If these models turn out to be even remotely accurate, our grandchildren and great-grandchildren will certainly take care of very different plants in their Ohio gardens than you and I take care of ours!

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So, what’s a gardener to do?

There are some things we can all do in our gardens and home landscapes to mitigate the effects of climate change, including the following:

∎ Plant more trees to absorb carbon dioxide

∎ Convert kitchen and garden waste into compost

∎ Reduce water consumption (think drip irrigation)

∎ Reducing the risk of the spread of invasive species

∎ Improve your energy efficiency

∎ Reduce the use of gasoline-powered garden and garden tools

Many gardeners making small changes can have a big impact on mitigating the negative effects of climate change.

Mike Hogan is an Extension, Agriculture and Natural Resources teacher and associate professor at Ohio State University Extension. hogan.1@osu.edu

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