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2012-02-16

-- In the Wild -- USDA releases new hardiness zone map

By Carolyn B. Edwards BCC Staff Writer


After 22 years, the USDA has finally released a new hardiness zone map for the US. According to Bert Cregg, posting on Washington State University's blog, The Garden Professors, there are several reasons why that is good news.

First, says Cregg, the old map was 22 years old. Secondly, the versions of the map that were available electronically did not reproduce well and had poor resolution when you tried to zoom in on a particular area. This sometimes made it difficult to identify the hardiness zone for certain locations and limited the utility of the map for presentations and publications.

Many also felt the map didn't accurately reflect more recent climatic conditions, added Cregg.

In 2006, the National Arbor Day Foundation released an updated hardiness map using more current climatic data that placed many locations at one or even two hardiness zones warmer than the 1990 USDA map.

The new USDA map is easily downloadable. You can key in a zipcode to find a zone. You can zoom in or out. You can also select a roadmap or satellite background and choose different levels of transparency or opacity.

To access the map, go to

http://planthardiness.ars.usda.gov/PHZMWeb/

The town of Bandera and the southeastern part of the county is now in Zone 8b where the minimum temperatures average 15 to 20 degrees Fahrenheit. Medina, and the northwestern half of the county are in Zone 8a, where minimum temps range from 10 to 15 degrees.

It's important to remember that hardiness zone maps are based on average annual minimum temperatures.

That is, they are based on the lowest temperatures we are likely to see in an average year, said Cregg. "Not sure about where you live, but I have yet to see an average year in my adult life."

Lots of gardeners love to push the boundaries of their hardiness zone.

The USDA hopes its new map will be the standard by which gardeners and growers can determine which plants are most likely to thrive at a location. The map is based on the average annual minimum winter temperature, divided into 10-degree F zones.

The map is available as an interactive GIS-based map, for which a broadband Internet connection is recommended, and as static images for those with slower Internet access.

No posters of the USDA Plant Hardiness Zone Map have been printed.

But state, regional, and national images of the map can be downloaded and printed in a variety of sizes and resolutions.