USDA cold hardiness zone map
This map follows the UDSA cold hardiness system, which is based on the average minimum temperatures in each area and gives a guideline for plant adaptability. Plant material on our website is related with a USDA zone number, which is correct to the best of our knowledge. Zones can be divided further into “a” or “b”. When used, “a” refers to the colder half of the zone and “b” to the warmer half.
For example, Zone 4a indicates temperatures of -25 °F to -30 °F. However, we cannot be responsible for hardiness since growing conditions, site selection and ununsual winter weather will affect winter survival.