In Canada, Agriculture Canada has mapped out the average coldest temperature in each area and uses this to create what it calls “plant hardiness zones.” Though useful as a guideline for gardeners, it does not tell the full story. There are many factors that affect hardiness of plants. One of the most important is local conditions. In wintertime, consistent snow cover is key to plant survival as it acts as an insulator to plants. Some plants will be more likely to survive in a consistently snow-covered zone 4 garden than in a bare zone 6 garden. Haliburton County is generally considered to be zone 4.
There may also be areas of 'micro climates': an area where the conditions of the zone may be moderated or made more severe by other factors. For example, in urban areas where concrete and brick absorb the heat, releasing it into the ambient air may support species that might otherwise not survive. Likewise a north facing slope may remain colder longer.
Use your plant hardiness zone information and your local conditions when you purchase new plants to ensure they will survive. Beware of Imported plants that have the US hardiness zone information on the tags. This is not equivalent to Canadian hardiness zones. Buying locally and asking questions at your local garden centre will help alleviate this confusion.