Hardiness Zone Confusion?

Q: When I look at certain plants and seeds it appears that I am in different zones? Some packs of seeds say I am zone four, but here it says zone 6. Am I losing it or is there a reason for this?

Hardiness Zone: 6a

Thanks you!
Katie from PA

A: Katie,

It's not surprising that you've experienced some confusion over which hardiness zone you're in. Currently, there are at least three different hardiness zone maps floating around on the Internet, in books, magazines and seed catalogs. The USDA created the first U.S. hardiness zone map in the mid 1900's. Since then, Agriculture Canada and Harvard University have also come out with maps. In 1990, the original USDA map was updated by further dividing the zones into 'a' and 'b' (representing the higher and lower temperature ends in each zone). This latest 1990 map is the most commonly accepted version in use today.

The American Horticultural Society is currently working on yet another version of the 1990 hardiness zone map for the USDA. As of now, there is no word on when the new map will be ready. Thirty years worth of climate data, including the length of cold spells and airflow patterns are being studied to determine the new hardiness zones. The new version of the map will no longer feature 'a' and 'b' distinctions in each zone and will include 15 zones instead of 11 to reflect growing regions for sub-tropical and tropical plants.

Until then, if you're interested in complicating your gardening life even further, check out the American Horticultural Society's website and read about your "Heat Zone." http://www.ahs.org/publications/heat_zone_map.htm

Ellen