Last week, the United States Department of Agriculture (USDA) updated their national Plant Hardiness Map to reflect data collected over the period 1974 to 2005.  (The previous map had been released in 1990, and used data from 1974-1986).  The new map adjusts the hardiness zones of the country to reflect a warming climate – there’s a 5 degree Fahrenheit difference between the 1990 zones and the 2012 ones.  While that may be enough to push certain American gardeners out of their previous hardiness zones into a new one, it’s still necessary, when actually getting out and digging in the dirt, to consider microclimates and all of the other climatic factors that comprise “plant hardiness.”  It’s not just about neat and tidy labels:  plants are alive, after all, and they don’t always grow where we think they should.   Anyway, the new USDA map is also interactive:  American citizens can plunk in their zip code and a search engine will tell them what zone they live in.  I guess that’s good if you don’t want to look at the map and interpret the colour codes.   If you’re interested, you can check out the new map here.  (Sometimes the USDA zones are referenced in Canada as well, especially when plants are traded back and forth between the two countries).

Here in Canada, our non-interactive Plant Hardiness Map is not merely based on the average annual extreme minimum temperature (read:  average minimum winter temperature) like the USDA map is:  ours includes many more climatic variables, such as the length of frost-free period (live anywhere in this country for at least a single gardening season and you’ll understand why this is so important), summer rainfall, maximum temperatures, snow cover, and maximum wind speed, among others.  Our most recent map was released in 2000, and updates the original map from 1967.

I’m not sure when the government began the project, but it seems that they’re making the humungous effort to further break down our current plant hardiness zones into “Plant Specific Zones”:  they want to figure out where exactly in Canada you can grow specific trees, shrubs, and perennials, and map that information – plant by plant – for the benefit of gardeners and farmers across the nation.   Because this is such a monumental undertaking, they’re soliciting the assistance of people all across Canada to furnish them with data about what plants are surviving in their geographical region.  So, if you want to let them know that your white bleeding heart is thriving in Winnipeg, or your emerald cedar is doing well in Edmonton, you can register on this site and tell them.  Obviously, the maps will only be built as quickly as the data is sent in, and by nature, will be ever-evolving.  Due to inevitable gaps in information, these plant-specific maps may only have a limited usage, but just like the Plant Hardiness Map, they should provide an excellent framework for gardeners to start with.