The US Department of Agriculture released the 2012 Plant Hardiness Zone Map, it is the first update provided by the USDA since 1990.
According to the USDA website,
"The 2012 USDA 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 the USDA website. "The map is based on the average annual minimum winter temperature, divided into 10-degree F zones."
Developed together with the Oregon State University, the new map has several changes including two new zones for Hawaii and Puerto Rico and many zone boundaries have shifted. There is a switch in temperature as well, with many zones reportedly 5 degrees warmer than the previous map.
What is the cause for the change? No, global warming is not the cause. The new map was created using data collected from a 30 year period that spanned from 1976 to 2005. The previous map contained data from 1974-1986, a thirteen year period. Newer, more sophisticated methods of data collection were used, taking into consideration, nearness to bodies of water, position on the terrain & change in elevation. In addition, data was collected from many more weather stations than before helping to increase the accuracy of the map.
For the first time, no posters of the PHZM will be printed; instead, the map is available as an interactive GIS-based map. State, regional and national maps can be downloaded and printed in a variety of sizes and resolutions from the USDA website. (http://planthardiness.ars.usda.gov). The interactive map is easy to use, enter your zip code then click on the map to view your hardiness zone.
What does this mean for gardeners? If your zone has changed, it does not mean you have to remove plants from your garden. If a specific plant is doing well in your garden, it should continue to do well. As a gardener, you should refer to the new hardiness zone when selecting new plants, shrubs and trees for their gardens. You should also keep in mind that many factors such as soil type, moisture, humidity, light, pollution and heat could all play a factor in the well-being of your garden plants.
USDA Plant Hardiness Zone Map, 2012. Agricultural Research Service, U.S. Department of Agriculture. Accessed from http://planthardiness.ars.usda.gov.