Hardiness zones provide information by which gardeners and growers can determine which perennial plants are most likely to grow at a location. Canada and the US each use different, not interchangeable plant hardiness zones labelled with numbers and letters. Zones in Canada provided by National Resources Canada are determined by a variety of climatic conditions, including rainfall, frost-free periods, maximum snow depth, and more.
Canada’s plant hardiness zones range from 0, where weather is extremely harsh, to zone 8 which comprises certain areas along the west coast of British Columbia. American zones published by the United States Department of Agriculture (USDA) are based on the average lowest temperatures experienced in a region each year.
Canada Plant Hardiness Search
National Resources Canada has developed an online tool that provides an alphabetic list of plant information. The list provides common or Latin name search options for hundreds of plants by different time periods, municipality and geographic data.
Urban Sprawl & Micro-climates
Regardless of sophisticated calculations, hardiness zone conditions are unstable as the climate is changing. Additional factors created by micro-climates such as terrain features, bodies of water, wind, fire or smoke or even buildings and human activities make it difficult to determine whether plants can survive in certain areas or not.
Does Plant Hardiness Information Matter ?
Yes and No. Canadian and USDA plant hardiness information has been updated a few times in past decades but as climate change progresses, hardiness information can only serve as an approximate guide. Plants which grew for years in one zone no longer exist and others which never managed to establish, now thrive.
A plant that experiences zero degrees could be damaged and recover but will die with extended periods of cold. Combinations of wind, cold and humidity impact various plants differently. Temperature fluctuations are tough on most plants. The best practice is to plant native species that grow in a present zone rather than seeking exotic plants that are hard to look after.
Plant Problems – Fruit Tree Gummosis
Using USDA Zones in Canada
As no simple conversion systems exist to use USDA zones for Canada, a non-scientific method is to simply add one zone to the designated USDA zone. For example, USDA zone 4 is roughly comparable to zone 5 in Canada.
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