North American Fruit Explorers mailing list at ibiblio

["M Stanton" <6ducks@fuse.net>]

The USDA climate zones (the ones you see referenced in plant catalogs, i.e. ‘grows in zones 5-8’) are based on the average winter low temperatures as observed over many years.

The American Horticultural Society has devised a heat zone map based on the number of days (in an average year) where daytime highs are 86 F. or greater.

They can be accessed here:  http://www.ahs.org/publications/heat_zone_map.htm

 

My favorite maps for horticulture students are the Sunset climate zones, which take into account a variety of factors besides hot and cold, such as growing season length, ocean influence or lack thereof, wind patterns, aridity or humidity of the climate in general, etc.  Sunset maps can be accessed here along with a discussion of pros and cons of using zone maps:  http://www.backyardgardener.com/zone/

 

 

 

 

Michele Stanton