New USDA Winter Hardiness Map

 By Richard B. Primack

 

“How little there is on an ordinary map! How little, I mean, that concerns the walker and the lover of nature… The wavering woods, the dells and glades and green banks and smiling fields, the huge boulders, etc., etc., are not on the map, nor to be inferred from the map.” Henry David Thoreau in his Journal.

 

The U.S. Department of Agriculture’s “plant hardiness zone map” was updated several weeks ago for the first time in a decade, providing guidance to gardeners and other plant growers about which flowers, vegetables, and shrubs are most likely to thrive in a particular region.

Figure 1: New Plant Hardiness Zone Map

The key information on the map is the lowest likely winter temperature in the various regions, which is important for determining which plants are likely to survive the season. Across the lower 48 states, the lowest likely winter temperature overall is now 2.5 degrees (1.4 degrees Celsius) warmer than when the last map was published in 2012, with over half of the regions having shifted to a warmer plant hardiness zone. 

Figure 2: In coming years, Camellias will be growing in Boston as the climate continues to warm. 

This surprisingly rapid shift in just 10 years is due to temperatures in the winter and at night rising faster than those in the summer and during the day.

As demonstrated by this shift in the hardiness zones, climate change is already having strong impacts on plants and the people growing them in the United States. As the climate continues to shift, it can be tricky for plants — and growers — to keep up. Warmer temperatures may mean that some plants will now die during summer heat waves, and that insect pest outbreaks may become more severe as milder temperatures make it easier for them to survive through the winter. 

For more info on the changes made to the map, see this article: LINK