Hardiness Zones

There are numerous resources out there that will determine your hardiness zone but the one I typically refer Canadians to is the Agriculture Canada online app.  As is typical of many of our government initiatives, it is somewhat clunky and inefficient, but it means well and actually provides very useful information.  This app will allow Canadians to zero-in on their city/region, and even their specific neighbourhood, to determine their hardiness zone, and it also allows users to toggle between the 2000 Hardiness Zone Map and the 1967 version.

It seems that the 1967 version suggests that many Canadians live in a slightly higher hardiness zone than the 2000 version.  The 2000 version, which is based on data collected between 1961 - 1990, seems to be somewhat skewed by particularly cold winters in the 70's and 80's. Organizations in the US such as the American Horticulture Society and the US National Arbor Day Foundation have found a similar phenomenon which eventually led to the USDA updating its map in 2012 to reflect generally warmer winters since 1990. Agriculture Canada has yet to update its map.

This is the reason I list my hardiness zone as 6a/6b.  It is exceedingly rare for Oakville to experience a low of -20C or colder, and in fact, the coldest winter lows seem to hover around -16C to -18C and remain there for only a few hours during the night. That would put Oakville in zone 6b, though still at risk of an extreme cold snap every 10-20 years, a la January 2014!.  Still, even this year, the air temp hit a low of -21C, which would just barely bump Oakville into zone 6a.