by Laura Tattersall
What zone are we?
This depends where we live. It also depends what country you ask. The zone map and designation for Canadian zones is subtly different than the USDA zones. Plants sold in Canada are supposed to carry a Canadian zone designation. When reading magazines originating in the US, remember that by their system we are solidly zone 4b.
Another way of looking at it is by using coldest winter temperatures as a guide. USDA zone 4b corresponds to -28.9ºC to -31.6ºC. While Canadian zones take into account the minimum winter temperature, they also use length of frost-free period, summer rainfall, maximum temperatures, snow cover and maximum wind speed.
The Kingston and Gananoque areas where many of our customers garden are zone 5b. Parts of Kingston are certainly zone 6a (especially near the lake). Most of Ottawa is zone 5a, and Toronto is zone 6a.
Most plants actually have a range of zones they can live in, usually spanning 4-5 zones. This means plants designated zone 1 can live in zones 1 through 5. The furthest northern reaches of Ontario are zone 1, so a plant that is zone 1 is very hardy. Further south in the USA they have very real issues with it being too hot for some plants, but here we do not have to concern ourselves with the issue because of the range.
To re-cap, in the Kingston area we can grow plants designated zones 1 through 5b, and often right up to zone 6b.
Can I grow plants from outside my zone?
Plants from lower numbered zones (1-4) can be easily grown in zone 5, and will often give the best results as they are extra hardy. Plants from zone 5 can also be grown easily in most locations. Growing plants designated zone 6 is possible, but can lead to disappointment. Trying to grow plants with less cold tolerance is often called pushing zones. When you are pushing zones, try to find a location that is not windswept in winter, has good snow-cover and meets other requirements of the plant (shade/sun/dry/wet). A plant that is unhappy going in to winter is much less likely to survive. Plants should be well rooted, so late season planting when pushing zones is a bad idea. Providing temporary snow fence to the west of an area can help, as can planting in areas shaded during winter (these areas may be in the sun in summer). Properties very near large bodies of water often are easier to push zones in, as are properties with windbreaks. Pushing zones can be successful, and gives us a much larger pallet of plants to choose from. On the other hand, it often leads to tears, and with so many wonderful plants available that grow easily, it might be more satisfying to stay within your zone.
My friend who lives in North Bay can grow this, why can’t I?
Kingston is prone to having a big thaw in late January, then re-freezing. This creates some of the worst possible conditions for overwintering perennials. No snow cover and bitter cold with wind will be very hard on perennials. Properties in areas where there is reliable snow cover (North Bay for example) can often push zones for herbaceous perennials (perennials that die back to the roots) very easily. Mulching heavily with leaves in the fall, laying evergreen boughs on the gardens and shoveling snow on to your perennial beds are all techniques that help in overwintering perennials.