Hardiness Zones, the Canadian way
Oro-Medonte Horticultural Society Column by Lynne Melnyk
Living next to the United States means that we are exposed to their way of doing things, including their hardiness zone maps. We have all seen US zones on plant tags or the infuriating maps in gardening magazines that stop at our borders. So why don’t they show our zones and can we use the US zones for choosing plants for our gardens? It’s complicated.
A plant hardiness zone map shows what can grow where. Last year the US put out a new version of their hardiness zone map. They use two criteria, extreme cold and extreme hot, to work out the different zones. In Canada, Natural Resources Canada compiles an equivalent map but use seven criteria, such as the mean minimum and maximum for the coldest and hottest months, rainfall, snow depth, and maximum wind gust in 30 years. This complexity of data means that, for instance, a Zone 6 in the states is not a Zone 6 here nor can we use the old rule of thumb of dropping a zone for Canada.
Natural Resources Canada is planning to issue an updated map in 2024, the first since 2014, but it hasn’t shown up on their website so far. They expect to see more change in the far North and the West. The past 50 years, prior to 2014, saw an increase of 3 zones in the West and a half zone in the East, so we can expect some increase but not too drastic. As the far North is warming faster because of the climate crisis, there may be some alarming increases.
NRC also produces a map that is equivalent to the US map using minimum and maximum temperatures.
You can also search by municipality on the NRC website; Barrie, Midland and Orillia are all 5A. While the map can be helpful when purchasing plants, we all have microclimates or colder areas in our gardens. I have had various plants that were hit hard by frost in the spring while others a few miles away were fine.
We can all contribute to future maps by letting NRC know what is growing in our gardens. Go to the Plant Hardiness Zone Maps page on the NRC website, www.planthardiness.gc.ca/?m=1,click on ‘Plants in my area’ and fill in and upload the information.
These maps are from the Natural Resources Canada website.
Oro-Medonte Horticultural Society has two more upcoming meetings for 2024:
October 21, Kenneth Brown will speak on creating, maintaining and harvesting a vegetable garden.
November 18, Molly Shannon on everything you want to know about succulents, for both indoors and outdoors.
Visitors are welcome, come at 7 p.m. for refreshments and to meet our friendly members. Both meetings take place at 7:30 at the Community Arena & Banquet Hall, 71 Line 4 North, corner of Hwy 11 S and 4th Line N.
Details for all events can be found on our website: www.oromedontehorticulturalsociety.ca.
