As Plants Migrate North, USDA Revisits Hardiness Zones
The USDA has a new map of plant hardiness zones for 2012. Last updated in 1990, the map divides the United States, including Puerto Rico, into 13 separate zones representing regions of minimum average winter temperatures. The map is divided into 10˚F zones.
Zone boundaries in the new map have shifted as many warmer zones trek farther north; plus there are two new zones. As the map shows, winters aren’t as cold as they were in most places and spring blossoms come earlier.
“Some places have gotten warmer and some places have gotten more accurate,” said Kim Kaplan, chief of special projects for the USDA.
Some of the shifts in boundaries are the result of more sophisticated mapping says the USDA. For the first time, the new map takes into account the effects of elevation, large lakes, and whether a place is located in a valley or on top of a ridge. They admit that most of the changes were due to using temperature data from recent years, which have been record crushers.
You can check out the map yourself at the USDA website.