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  • Writer's pictureKate Duke

ALL ABOUT HARDINESS ZONES

Updated: Feb 16

Written by Kate Duke


It's been a while, but Neighbours Tree Company is back with another 'blog' for you. This time, we are taking on the basics of Tree & Plant Hardiness Zones.


You may already know all about tree zones, perhaps you've seen the reference on your tree tags, or maybe you haven't noticed those seemingly insignificant numbers at all; whatever the case, Hardiness Zones are an important factor in the planning and design of your properties' hardscaping. So let's get into it..


WHAT ARE HARDINESS ZONES?

Simply put, Hardiness Zones are a set of values that designate climates into a scale, which allow for you to choose plants and trees that have the best chance of surviving in your area. While the original premise of hardiness zones first popped up in the US in the 1920's, it was later nailed down by Agriculture Canada and the USDA (United States Department of Agriculture) in the early 60's, with adaptions having been made in many countries around the world. The USDA method designates zones based on the Average Annual Extreme Minimal Temperatures, and Canada has adopted both this system and a more multivariate approach simply called "Canada's Plant Hardiness Zones". Other entities, such as the UK Royal Horticultural Society, base their scales on extreme heats averages. For now, let's stick to North America!


Climate change and increased knowledge has seen the creation of more zones being added to these scales, which is continuously being updated. In 1920, the US had 8 zones that broke down into 10 degree Farenheit incriments, in 1960 the USDA designated 10 zones, and more recently has grown to 13 zones, with 5 degree incriments, PLUS the addition of 'a' and 'b' breakdowns for each. The USDA scaling system now has 26 zones, written as 1a, 1b, 2a, 2b and so on until you reach 13a and 13b. The Canadian Hardiness Zones range from 0a, 0b, 1a, 1b etc up to 9a, and goes quite a bit deeper than the USDA scale. Our Canadian Plant Hardiness Zones consider multiple climate variants and parameters including average heat, precipitation, maximum snow depth and frost free days, using climate interpolation techniques from numerous locations across the country. Two maps have been released to reflect the change in our climates, one being from 1961-1990, and the other reflecting 1981-2010.



WHERE DO I FIND MY ZONE?

In Canada, the best resource for finding zones would be through www.planthardiness.gc.ca Here you can find not only your zone, but can also find a list of plants/trees that have been designated for your zone. There are maps, search engines and more for you to utilise!


Once you know your zone, you'll want to ensure any plants or trees you bring in meet AT LEAST that standard. For example, if you have discovered you live in Zone 3, you'll want to ensure your plants and trees can withstand AT LEAST Zone 3 extremes; meaning you can also open your options to plants and trees that are designated for zones 1 and 2. Anything below 3 would likely not thrive, or potentially even survive, through our extreme cold, frost and snow averages.



Canada.ca Hardiness Zones website
Canada.ca Hardiness Zones website



HOW DO I KNOW WHAT ZONE A PLANT/TREE IS DESIGNATED FOR?

Once you know what to look for, the information is very easy to come by. You can always use the search engine mentioned above or by researching each tree, but alternatively, plants and trees should have their zone requirements listed on their tags as shown below (note, these may be indicative of USDA Zones). If you are ever in doubt, your local nursery should be able to readily provide you with this information as well.



WHAT ARE SOME EXAMPLES?

Let's stick close to home here! Let's say you live close to our shop in Sherwood Park, Alberta. The zone here (as of 1981-2010) is 3b (previously 4a), meaning you are best to choose from this zone, but ok to choose from trees listed in zones 3a, 2b, 2a, 1b, 1a, and so on. Your best bet (although not totally necessary) is choosing trees or plants native to your area in this zone.

Some of the more common plants in the zone 3 group are Maple, Birch, Ash, Spruce, Poplar, Tamarac, Oak, Lilac, Flowering Crab Apple, Fir, Hemlock, Elm, Dogwood, Beech, Cedar and Willow.


With all this being said, there are many factors that go into the effective planning of your hardscape, including space limitations and maintenance needs, as well as aesthetics. Neighbours Tree Company can dependably help in the planning of your trees and plants, and our team of arborists and horticulturists are available to assess your property and aid in your plans! We can be reached at 780-919-2302 or by reaching out through the Contact Us page here on our website!


Have beautiful days!!




Sources

National Resources Canada. “Plant Hardiness of Canada.” Accessed on November 30, 2023 at http://planthardiness.gc.ca/ 

United States Department of Agriculture. “USDA Plant Hardiness Zone Map.” Accessed on November 30, 2023 at  https://planthardiness.ars.usda.gov/ 

McKenney, D.W., Hutchinson, M.F., Kesteven, J.L., Venier, L.A. 2001. Canada´s plant hardiness zones revisited using modern climate interpolation techniques. Can. J. Plant Sci. 81: 129-143.


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