What is plant hardiness zone

A hardness zone is a geographically defined area in which climatic conditions’ a specific category of plant life is capable of growing, including its ability to survive the minimum temperatures of winter.

The Canadian hardiness map prepared in 2000 by Natural Resources and Agriculture Canada is divided into nine major hardiness zones: the harshest is 0 and the mildest is 8. Relatively few plants are suited to zone 0.  In addition to zones, also subzones (e.g., 4a or 4b, 5a or 5b) are noted in the map legend. These subzones are very important to  gardeners, as they pinpoint to their garden location.

The hardiness zones differ even within the greater Toronto area. For instance, Mississauga and Oakville fall into zone 6b, Brampton 6a and Etobicoke 7a. That means that in most part of Mississauga only plants that survive in the lowest temperatures -20.6 to -17.8 C, should be planted, while this threshold is lower in some parts of Toronto, including Etobicoke, where this range is -17.8 to -15.0 C, and in Brampton where the range is lower between -23.3 and -20.6 C.