The zone numbers refer to the USDA scheme of denoting the minimum winter temperature. This scheme only uses 11 zone numbers for the U.S. ------------------------------------------------------------------------ Approximate range of Average Annual MINIMUM Temperatures. C=Centigrade/ F=Fahrenheit Zone 1 = below -45C/ -50F Zone 2 = -45C/-40C -50F/-40F Zone 3 = -40C/-34C -40F/-30F Zone 4 = -34C/-29C -30F/-20F Zone 5 = -29C/-23C -20F/-10F Zone 6 = -23C/-18C -10F/ 0F Zone 7 = -18C/-12C 0 F/+10F Zone 8 = -12C/- 7C +10F/+20F Zone 9 = - 7C/- 1C +20F/+30F Zone 10 = - 1C/+ 4C +30F/+40F Zone 11 = above+4C/ +40F ------------------------------------------------------------------------ NOTE: The dates below are for the Northern Hemisphere Zone 1 = Average dates Last Frost = 1 Jun / 30 Jun Average dates First Frost= 1 Jul / 31 Jul Note: vulnerable to frost 365 days per year Zone 2 = Average dates Last Frost = 1 May / 31 May Average dates First Frost= 1 Aug / 31 Aug Zone 3 = Average dates Last Frost = 1 May / 31 May Average dates First Frost= 1 Sep / 30 Sep Zone 4 = Average dates Last Frost = 1 May / 30 May Average dates First Frost= 1 Sep / 30 Sep Zone 5 = Average dates Last Frost = 30 Mar / 30 Apr Average dates First Frost= 30 Sep / 30 Oct Zone 6 = Average dates Last Frost = 30 Mar / 30 Apr Average dates First Frost= 30 Sep / 30 Oct Zone 7 = Average dates Last Frost = 30 Mar / 30 Apr Average dates First Frost= 30 Sep / 30 Oct Zone 8 = Average dates Last Frost = 28 Feb / 30 Mar Average dates First Frost= 30 Oct / 30 Nov Zone 9 = Average dates Last Frost = 30 Jan / 28 Feb Average dates First Frost= 30 Nov / 30 Dec Zone 10 = Average dates Last Frost = 30 Jan or before Average dates Last Frost = 30 Nov / 30 Dec Zone 11 = Free of Frost throughout the year. ------------------------------------------------------------------------ Frost: Light Freeze. damage depends upon length of frost duration. Light Freeze: -2C/-0C 29F/32F - tender plants killed with little destructive effect on other vegetation. Moderate Freeze:-8C/-2C 25F/28F - wide destruction on most vegetation with heavy damage to fruit blossoms and tender semi-hardy plants. Severe Freeze: -9C 24F and colder, heavy damage to most plants. ------------------------------------------------------------------------ Shade: Usually an area under a closed tree canopy that receives no direct sun at all. Partial Usually an area under a lone or limited Shade: number of trees receiving only a 1 to 5 hours of dappled sun during the day. Partial Usually refers to an area that receives Sun: approximately 3 - 5 hours of full sun per day. Full Sun: Refers to an area receiving 6 or more hours of full sun per day. ======== Sunset Magazine has developed a more extensive, and thus more informative scheme of zone numbers that includes more micro-climates. I don't know if it will work for Canada, but USDA zones for locations in the U.S. can be found using the following web site: http://www.timeinc.com/cgi-bin/vg-zonefinder