Plant Identification & Selection
Plant hardiness zones, native trees, deciduous conifers, annuals, perennials, biennials, and evergreen shrubs.
- Identify plant hardiness zones and their significance for plant selection in Canada
- Distinguish between native and non-native trees commonly used in Canadian landscapes
- Classify plants as annuals, perennials, or biennials based on their life cycles
- Select appropriate shrubs for specific landscape conditions including salt tolerance
Lesson 1
Plant Hardiness Zones & Climate
Understanding Canadian Plant Hardiness Zones
Plant hardiness zones are geographic areas defined by the range of climatic conditions that plants can survive. In Canada, the Plant Hardiness Zone Map is published by Natural Resources Canada (NRCan) and divides the country into zones from 0 (coldest) to 9 (mildest). Each zone is further divided into subzones (a and b), with "b" being slightly warmer.
2024/2025 NRCan Map Update
NRCan issued a major overhaul of the Canadian Plant Hardiness Zone Map using 1991-2020 climate data (replacing the previous 1981-2010 dataset). Approximately 80% of Canada shifted warmer by 0.5 to 2 full zones. Candidates must use the updated map - older study materials reflect outdated zone boundaries.
Key examples of zone shifts:
- Yellowknife: shifted from Zone 0b to Zone 1b
- Southern Ontario: expanded to Zone 6a/6b in much of the region (previously shown as Zone 5-6)
Updated Hardiness Zone Data
The 2024/2025 NRCan map replaces the old 1981-2010 dataset. If your study materials show southern Ontario as Zone 5-6, they are outdated. Current data places much of southern Ontario in Zone 6a/6b. Always use the current NRCan map for exam preparation.
How the Canadian System Differs from USDA Zones
The Canadian NRCan system is more comprehensive than the US USDA Plant Hardiness Zone map. While the USDA system uses only minimum temperature as its variable, the Canadian model incorporates 7 climate variables:
Canadian NRCan Model (7 Variables)
Mean minimum temperature of the coldest month
Frost-free period (days)
Summer rainfall (June-August)
Mean maximum temperature of the warmest month
January rainfall
Maximum snow depth
Maximum wind gust speed
US USDA Model (1 Variable)
Minimum average annual extreme temperature only
Does not account for summer heat, wind, or moisture
A plant rated USDA Zone 5 may not perform identically in Canadian Zone 5 due to different climate profiles
The NRCan index combines these 7 variables into a composite score from 0 to 92, which is then classified into zones 0 through 9 with a and b subzones.
Canadian Zone Reference
Selecting Plants for the Zone
Always select plants rated for your zone or colder. A plant rated Zone 6 can survive in Zones 6 through 9 but will not reliably survive in Zone 5 or colder. Microclimates within a landscape can shift the effective zone - south-facing walls, sheltered courtyards, and areas near heated buildings can be a half-zone warmer than the surrounding area.
The NRCan 2024/2025 Plant Hardiness Zone Map uses 1991-2020 data and 7 climate variables - not just minimum temperature like the USDA system. Approximately 80% of Canada shifted warmer. Southern Ontario is now shown as Zone 6a/6b. Always select plants rated for the local zone or colder.