Gardeners in Canada enjoy a varied climate and growing conditions across the expansive nation, much like gardeners in the United States. The colder winters and cooler summers find Canadians using at least three plant hardiness zone systems to inform their planting decisions. Plant hardiness zone maps act only as a guide, as Mother Nature always trumps man-made labels and systems no matter how concrete the designations may seem.
Agriculture Canada Plant Hardiness Zones
In 1967 Agriculture Canada created a plant hardiness map using Canadian plant survival data and climatic variables, including minimum winter temperatures, length of the growing season, summer rainfall, maximum temperatures, snow cover, winter rainfall and maximum wind speeds. The 2000 map was jointly created by the Canadian Forest Service and Agriculture and Agri-Food Canada using the same variables and more recent 30-year climate data, dating from 1961 to 1990. There are nine major zones, 0 through 8, each with two subzones (a/b).
USDA Hardiness Zones
The United States Department of Agriculture developed a plant hardiness map based solely on average winter minimum temperatures in 1960. Eleven zones, numbered 1 though 11, reveal coldest winter regions across the United States and Canada. Recently, the USDA map expanded to 15 zones to include winter minimum temperatures across all of North America, including Mexico and the Caribbean.
Sunset Climate Zones
The publishers at Sunset initially developed climate zones for the American inter-mountain West, and also coastal and southwestern Canada to help guide plant selection for gardeners across western North America. The Sunset system combines several factors in making the climate zones: winter minimum temperatures, summer temperatures, elevation, land formations, rainfall patterns, length of the frost-free season and proximity to oceans. The southern half of Canada received Sunset climate zone ratings: zone 1, 38, 39, 40, and 42 through 45 exist east of the Canadian Rockies, while zones 1, 2, 4 and 5 dominate in the West, including around Vancouver.