We are told that we are zone 3 here in Canmore. But on the Zone map it appears that we are 2a or 1b. What plants asre suitable for this zone?
If you drop with some regularity (once every 3-5 years) to temperatures of -40ºC or below, you've dropped into zone 2. Below -45ºC and that's zone 1. According to Ag. Canada, Banff is 2a.....Canmore may be marginally warmer (2b?) If you're trying to determine what shrubs and trees to plant, think zone 2a. If it's bulbs and perennials you want & you have consistent snow cover, think zone 4
With the USDA system zone placement is affected only if cold episodes are frequent enough to lower your average annual minimum temperature, based on a 15 (lately 13?) year period.
There are at least two factors in climate (many more actually) that will effect planting success, hence a single zone number is of only limited use in the real world. The two I'm referring to are "normal" extreme winter low temperature, which the zone numbers address and the "growing season" which is usually expressed in growing degree days, Corn heat units or a similar locally appropriate measure. The zone will predict survival or winter kill, while the others attempt to predict ripening success or timing. Then there's precipitation and timing of precipitation, elevation and relative elevation, slope amount and direction.... Ralph
