I would like to find out what garden zone we live in. I think it may be 5b, but want to confirm. We are in East York, Toronto, Ontario.
To determine zone number, Canada uses a formula that consists of 7 climate variables. Canada’s hardiness map is divided into 9 zones (from 0, which is the harshest, to 8, the mildest; sub zones (e.g., 5a or 5b) are provided for all zones except 8, which consists of 8a only). Toronto is generally considered Zone 6.
The Canadian approach is is very different from that of the US Department of Agriculture (USDA), which bases its system on average annual minimum temperatures; the USDA considers Toronto to be in Zone 5.
As well, in Canada, a hardiness zone change is afoot, with Toronto gradually moving from Zone 6a to 7a, based on updates using more recent data. For example, see Natural Resources Canada’s Plant Hardiness Zone by Municipality . Note that the “hardiness index” has changed in Toronto from 62 [1961-1990 data; this number corresponds to zone 6a] to 70 [1981-2010 data; this number corresponds to zone 7a]. See also Natural Resources Canada’s Extreme Minimum Temperature Models
It is important to be aware that, in some pockets of the GTA, the zones may be higher or lower. For example, if your garden is closer to Lake Ontario, it may be in Zone 6b or even 7. Further from the lake or in a more exposed area, your garden could be in Zone 5a or 5b. (in terms of Canadian Zones)
When selecting plants for your garden, choose those rated for more hardy zones, to maximize chances of survival. For example, if you have a plant that is hardy to Zone 5 and you live in Zone 6, the plant should be happy in your garden (as long as it receives appropriate care – e.g., sun exposure, soil type). If the plant is hardy to Zone 8, it won’t survive in your garden (although may work as an indoor plant that can survive outdoors in the summer).
Yours sounds like a simple question, but it’s not! Natural Resources Canada’s website includes several links intended to clarify the hardiness zones, but which seem instead to be very complicated and confusing.