Canada's Plant Hardiness Zone map was first published in 1967. In 2000 a new updated map was introduced. Although a good tool for deciding what plants will grow in your area, gardeners should be aware of some precautions in using this tool.
CAUTION # 1
Direct comparisons between the old and new maps could be misleading. The previous 1967 map consisted of 10 zones--nine of which (zones 0-8) were divided into `a' and `b' subzones. The new 2000 map consists of only 9 zones--eight of which (zones 0-7) are divided into subzones. Since there are unequal numbers of zones, it is impossible to equate a zone on the old map with one on the new map. It is unclear as to whether old zone 0 is similar to new zone 0.
The following table shows three possible ways of equating the two map zones.
1.0a=0a, 1a=1a, etc. This would mean former zones 8b and 9a have been completely eliminated.
2.0b=0a, 1a=0b, etc. i.e. new …