Planning this spring’s flowerbeds and gardens takes the chill out of our long prairie winters. Before you start planting, a good thing to know is your plant hardiness zone. Hardiness zones are defined by the average climatic conditions of each region; knowing your zone will help you determine whether or not a particular plant will grow in your area. The map is divided into nine major zones, the harshest is 0 and the mildest is 8 (for Canada).
Calgary and surrounding area falls into hardiness zone 3 with micro-climates of zone 4 in sheltered areas. How closely you stick to the zone guide might be relative to how much you love the plant, you never know, a plant rated to zone 4 or 5 may survive nicely, even thrive! Other variables like micro-topography, amount of shelter and local variations in snow cover will all have some effect.
Seed packets and catalogs usually indicate the zones for that type of tree, shrub or flower. Here’s how to translate: a zone 3 plant will endure winter temperatures to -40°C (-40°F), a zone 4 plant will tolerate temperatures as low as -35°C (-31°F) and so on.
Farmer’s Almanac – Frost Dates
Using the Government of Canada’s zone map along with the frost chart from the Farmer’s Almanac to estimate the last threat of frost (spring) and early average chance of frost (fall), you should be set to determine whether the plants you want will do well in your garden.
Using the Frost Chart, Calgary’s growing season is about 114 days in length. May 23rd (the estimated last date for frost in spring) to September 15th (when we might expect frost in fall). These are averages based on data collected over the years.
Zone chart references: wikipedia.org and Environment Canada