Plant Hardiness Map

Plant Hardiness Map

By: Shirley Martin

There’s a new map revealed that is receiving mixed response countrywide. 2015 marks the year Natural Resources Canada updated the plant hardiness zone map and many areas of our province saw a difference in their zone rating.  For example, Edmonton is now 4a while Lethbridge is zone 4b.  This is exciting news for those of us who endeavour to push zonal boundaries in our plant selection.

Zones are determined by a process of recording the average minimum temperature of the coldest month, amount of rainfall June through November, averaged maximum temperature of the warmest month, January rainfall, average maximum snow depth, and maximum wind gust in 30 years.  The new map uses averages from the period 1981 to 2010.

So, thrilled as you may be, there are still variances at play.  The map is not an absolute but rather a general guide with which you, the gardeners, can determine what will grow best in your area.  Consider it a tool.  You know your garden best.  You are aware of which area is the most blustery when it’s windy, which area holds the heat, in which area the snow lingers the longest, and which areas are most sunny and at what times.  These are all factors to take into consideration when selecting our most prized garden introductions. Your garden may differ depending on microclimates, elevation, and whether you are in the city or out in the open country.

Why the change?  This has been long coming, in my opinion.  We all know our climate has been changing.  Rarely do we see temperatures in the negative 40’s in the Edmonton region.  If you live in or have been to Medicine Hat, you know how hot and dry it can be in that region.  Our winters are a little more mild on average, we are experiencing more weather events worldwide.  Our plant zone map puts it in a visual form that justifies what we’ve known all along.  We are getting warmer.  If that means we can plant a greater variety of plants in our gardens, many of us silently cheer (not that we’re thrilled with climate change and what it means to our planet as a whole.)  After all, I’m not alone in yearning to someday being able to grow Japanese maples, am I?


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