Answer: The USDA zone numbers are based only on average annual minimum temperatures, i.e., how cold tolerant or "hardy" will any plant be. However, many more factors influence a plant's ability to thrive, including soil type (acid or alkaline; clay or sand), elevation, rainfall, humidity, etc. For example, zone 6 occurs coast to coast, in such varied states as Washington, Colorado, Tennesee, and New Jersey. Obviously the same plants are not all going to do well in all of these areas. So, the National Gardening Association developed the map with 'named' regions to take more of the factors into consideration. You are in USDA zone 6, closely bordered by zone 5. Zone 6 experiences average annual minimum temperatures of -10 to 0 degrees F. Zone 5 is -20 to -10 degrees. I hope this explanation helps!
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