What does that Hardiness Zone Number Really Mean?

Gardeners often hear the word ‘zone’ frequently during conversations with other gardeners or when reviewing plant tag descriptions. “What zone are we in?” or “what zone is that plant good for?” are often asked by fellow gardeners. What exactly are the answers to these questions and what do they really mean?

The first Canadian hardiness zone map was developed by Agriculture Canada in 1967. A newly updated and computer-generated map was developed in the mid 2000’s. Although this new map is more detailed and has used weather data for 30 years to determine the zones, the Rainy River District is still inaccurately classed. Our zone is indicated as a Zone 3a. I strongly disagree with this classification as I believe we are closer to a Zone 4a. The reasons behind this are the fact that there is not a weather station in Fort Frances but in International Falls. Agriculture Canada does not use U.S weather data to determine zones along the border, therefore we are lumped in with Kenora and Dryden for weather data. We all know just by watching the weather channel, how different the weather can be in Kenora, Dryden and Winnipeg from here in the District. The other reasoning behind a Zone 4a classification is the different forest type in the District. We are in a Great Lakes – St. Lawrence forest transitional zone and this type of forest does not survive north of a Zone 4a in the rest of the province. The forest around Kenora and Dryden is Boreal forest and the Boreal forest is a colder climate forest. With this reasoning I have tried many perennials when living in Fort Frances, with a Zone 4 classification, with great success, and I encourage you to do the same.

What exactly does a zone classification mean? Zone classifications were developed for the horticulturist as a guideline to the winter survival of trees and shrubs winter hardiness in the different growing regions of Canada. Today nurseries and gardeners use the zone classification system as a guideline for planting not only trees and shrubs but also perennials in their regions. Although not a precise method it is a good guideline for determining which perennials will be winter hardy in our area. Now remember this is a guideline only and there is always a chance that a perennial with a higher zone rating could out perform a perennial with a lower zone rating based on your individual growing conditions or you may not be able to grow Zone 4 classed perennials at all.

I certainly encourage you to use the zone classification system when planning your garden and when purchasing trees and shrubs for your landscape. I will stand by my theory for zone classification and I personally use Zone 4 as my upper limit for perennial winter hardiness in the Rainy River District so anything classed a Zone 4 or lower (to a Zone 1) should be winter hardy in the region. But I also to encourage you to try some interesting plants like bamboo and pampas grass from higher zone ratings, with the expectation that these will be interesting annuals in our area. I will try plants such as these from seed as opposed to purchasing as expensive potted plants, therefore if they do not perform well, I haven’t invested a great deal of money. I also will try trees and shrubs from a higher zone rating but only if I can get them in the smaller, more economical pots. Just keep these rules of thumb in mind if you travel out of our area and see an interesting plant you want to add to your own yard or garden.

I encourage you to have fun and experiment and keep the zone hardiness in mind. Using it as a guideline will help you make wise plant selections and will ensure that you remain pleased with your garden from year to year. Good Growing this season!