I wonder if anyone successfully grows Clematis montana in Toronto area without protecting them in any way in winter? I am struggling with keeping my hydrangea macrophylla blooming and do not want to add another useless plant to my garden.
Thank you for contacting the Toronto Master Gardeners.
Clematis generally fall into three different categories, based on bloom time. They bloom on either last seasons growth or on new growth. You will need to determine which variety of clematis you have growing by your porch before going ahead and pruning.
Clematis montana is an early flowering group of clematis. They typically bloom in April and May, from buds produced during the last growing season. These plants are pruned immediately after blooming, but no later than the end of July in order to give the plant enough time to produce new buds for next year. Start by removing shoots that have bloomed. If necessary remove dead or damaged stems. If growth is congested then cut out older stems to the base and thin the rest. Avoid cutting far into the main woody trunks. Cutting off too much may affect next years flowering. This group includes C. alpina, C. macropetala, C. armandii, C. montana, and C. chrysocoma.
Within this group of Clematis are a number of varieties; depending on which on you choose will determine whether they are hardy in our zone or not. For example C. montana ‘Tetrarose’ is hardy to zone 5a, whereas C. montana ‘Elizabeth’ is hardy to zone 6 and depending on where you live in the GTA you might be pushing the envelop with a zone 6 plant.
Toronto’s hardiness zone is 6. However, areas of the city exposed to wintery blasts may be closer to zone 5. When determining plant hardiness you must pay particular attention to the plant label. The Canadian approach is is very different from that of the US Department of Agriculture (USDA), which bases its system on average annual minimum temperatures; the USDA considers Toronto to be in Zone 5.
The following information on determining plant hardiness is from one of our earlier posts:
“To determine zone number, Canada uses a formula that consists of 7 climate variables. Canada’s hardiness map is divided into 9 zones (from 0, which is the harshest, to 8, the mildest; sub zones (e.g., 5a or 5b) are provided for all zones except 8, which consists of 8a only). Toronto is generally considered Zone 6.
As well, in Canada, a hardiness zone change is afoot, with Toronto gradually moving from Zone 6a to 7a, based on updates using more recent data. For example, see Natural Resources Canada’s Plant Hardiness Zone by Municipality . Note that the “hardiness index” has changed in Toronto from 62 [1961-1990 data; this number corresponds to zone 6a] to 70 [1981-2010 data; this number corresponds to zone 7a]. See also Natural Resources Canada’s Extreme Minimum Temperature Models
It is important to be aware that, in some pockets of the GTA, the zones may be higher or lower. For example, if your garden is closer to Lake Ontario, it may be in Zone 6b or even 7. Further from the lake or in a more exposed area, your garden could be in Zone 5a or 5b. (in terms of Canadian Zones)
When selecting plants for your garden, choose those rated for more hardy zones, to maximize chances of survival. For example, if you have a plant that is hardy to Zone 5 and you live in Zone 6, the plant should be happy in your garden (as long as it receives appropriate care – e.g., sun exposure, soil type). If the plant is hardy to Zone 8, it won’t survive in your garden (although may work as an indoor plant that can survive outdoors in the summer).”
Hope this helps!