The warmer regions of Canada, in USDA hardiness zones 3 through 7, can enjoy various hydrangea species in the garden. Some winter protection from bitter cold and snow ensures the dormant hydrangea plants survive, regardless of location. However, in the far north, western mountains and interior few hydrangeas can handle the coldest of Canada's winters. Select the appropriate hydrangea species for your climate.
Native to eastern Asia, the climbing hydrangea (Hydrangea anomala subsp. petiolaris) is an elegant vine that clings to tree trunks or building facades. It grows from 20 to 60 feet in height and is hardy in USDA Zones 4 through 8, much of southeastern and Pacific Canada.
Among the most cold tolerant of all ornamental hydrangeas, the smooth hydrangea (Hydrangea arborescens) is native to the eastern United States, being hardy in USDA Zones 3 to 7 and a bit warmer. Popular varieties of this species include 'Annabelle' and 'Grandiflora.'
Summertime is particularly grand with the color-changing blooms of the bigleaf hydrangea (Hydrangea macrophylla), with blue flower occurring in acidic soils and pink blooms in those that are alkaline. Native to Japan, these hydrangeas are also often forced into bloom by florists to sell as seasonal house plants. Outdoors they are appropriate only the warmest parts of Canada, USDA Hardiness Zones 6 and higher.
Also extremely cold hardy is the white-flowering peegee hydrangea (Hydrangea paniculata), native to Japan and southeastern China. It becomes are large shrub to small tree, and is a successful Canadian garden plant in areas with a USDA Hardiness Zone rating of 3 to 8.
Native to the eastern United States and extreme southernmost Canada around the eastern Great Lakes, the oakleaf hydrangea (Hydrangea quercifolia) is garden-worthy in USDA Zones 5 and higher. The foliage is attractively lobed and flushes red and burgundy in autumn. There are many selections from which to choose, including 'Alison', 'Harmony', 'Snowflake' and 'Snow Queen'.
Like bigleaf hydrangea, the villosa hydrangea's (Hydrangea aspera) flowers blush according to soil pH. This species is hardy only in the warmest areas of Canada, USDA Zone 7 and higher.