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.
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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
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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.
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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.
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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.
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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