What is a hardiness zone?
Canada has nine zones, ranging from 0 (the harshest) to 8 (the mildest). Each zone is divided into two parts, with “a” being harsher than “b.” In creating the zone map, minimum and maximum temperatures, snow cover, rainfall, wind patterns and the average number of frost-free days were all taken into account.
But as gardeners know, our weather patterns vary from year to year, especially with the effects of global warming. In addition, the location (south side versus north side) of your plot can affect the growing conditions of your plants.
How do you use it?
As a general rule, if you live in Zone 6, you should have good success with plants hardy in Zone 6 and up to three zones colder. Plants hardy to Zone 8 would never survive the winter in your yard. So, although the zone map is a useful starting point for all of us, consider your own yard’s conditions and your area’s weather fluctuations when choosing yearly plantings.
Here are some links to help you determine what zone you're in.
- Agriculture Canada Hardiness Zone Map
- The Old Farmer's Almanac Hardiness Zones page
- Going Beyond the Zones Project
- USDA Plant Hardiness Zone Map
- Environment Canada's Frost Dates Chart
About the Canadian Plant Hardiness Zone Map
The Canadian Plant Hardiness Zone Map was revised in 2000 (using weather data from 1961 to 1990). As well as plant survival data for trees and shrubs (the northern and southern extremes where a given species can survive and reproduce successfully), the effect of elevation and climate-change models were added to the equation.
At the nursery
If you live in Zone 5, look for plants that are hardy to Zone 5 or lower (plant labels don’t differentiate between parts “a” and “b”). Perennials from Zone 6 or higher will likely be sold as annuals in your area, since they aren’t guaranteed to survive the winter. Ask your garden centre professional for help with queries and suggestions.