A hardiness zone is a climate-based aid for choosing plants expected to survive outdoors over more than one season. Canada’s numbered zones run from 0, the harshest, toward 9, the mildest. Subzones a and b refine the scale: within a numbered Canadian zone, a is the lower hardiness-index band and b the higher band. For example, 4a and 4b are different bands within zone 4. A zone number is not a planting date or a prediction for tonight’s temperature.
The Canadian and USDA systems are different. Canada’s main map combines seven climate variables, including winter and summer temperature, frost-free period, precipitation, snow and wind. USDA zones use average annual extreme minimum winter temperature. Natural Resources Canada publishes Canadian-system maps and a separate USDA-style extreme-minimum-temperature map for Canada. Identify which system both the plant rating and your site lookup use. Never convert them by automatically adding or subtracting one zone.
Start with Natural Resources Canada’s map or municipality lookup, record the map edition and system, then confirm the exact species or cultivar with the nursery. The current Canadian map update uses the 1991–2020 climate period. A municipality or postal-code area is a starting location, not a measurement of the conditions beside your wall. This suite does not automatically assign a zone from a neighbourhood name or guarantee winter survival.
A perennial can live for multiple years, but only if it is suited to the climate and site. Annuals complete their life cycle in one season; some plants sold as annual bedding plants are actually tender perennials grown for one summer here. Tender annuals need frost-safe planting conditions. Cool-season annuals can have different cold tolerance. “Annual” therefore does not mean every plant can go outside on the same day, and “perennial” does not mean every cultivar is hardy in Montréal.
Microclimate and growing conditions still matter: observe wind, winter sun, snow cover, drainage, salt and exposure. Roots in an exposed container face different winter conditions from roots in the ground, so an in-ground rating is not a container-survival guarantee. Leave unmeasured conditions as unknown and resolve them with a site assessment. Mature height and width, sunlight and moisture remain separate checks even when the zone looks suitable.
The date picker uses meteorological seasons: spring March–May, summer June–August, fall September–November and winter December–February. Early March is therefore labelled spring, but that label does not make a frozen or snow-covered garden ready. The month windows below are broad planning prompts for Montréal, subject to forecasts, workable soil, stock type, plant-specific needs and aftercare. They do not use a fixed last-frost date, forecast weather or authorize watering outside municipal rules.
Planning note. Sources checked October 9, 2026. Planning suggestions, horticultural facts and municipal rules are kept separate: confirm anything that depends on your plant, site or address.