No one should be surprised by cold weather in December. The general absence of extreme temperatures in Vancouver often lulls us into of a false sense that we are living in a benign climate. But the plants in our gardens, both the survivors and the ones that die are indicators of just how cold it can get here. Although it might seem counterintuitive, some garden plants are better off being exposed to the full force of winter’s wind and cold. Many of the plants in the E.H. Lohbrunner Alpine Garden come from alpine and montane regions. Compact growth, consistent flowering and freedom from disease often derives directly from the plant experiencing cold temperatures (“chilling”), but a cold period in December is often extremely beneficial. Early chilling ensures that tissues become effectively dormant before potentially damaging mid-winter deep freezes. The Alpine Garden was designed precisely for maximum exposure.
The other side of the coin is protection—an important consideration for woodland plants and those that hail from milder winter climates. Many of our spring flowering trees and shrubs (rhododendrons and magnolias, for example)fit this description. Overall, the Botanical Garden derives significant climatic moderation from the predominantly moist, mild, westerly winds that flow off Georgia Strait. The significant tree cover in the David C. Lam Asian Garden, Carolinian Forest Garden and BC Rainforest Garden provide much needed shade in the summer. In the winter, winds sometimes shift around to the east, and when they do, they generally bring cold and dry conditions. This is when the upper forest canopy is critical in protecting understorey plants from excessive freezing and desiccation.
Submitted by Douglas Justice, Associate Director, Horticulture & Collections, November 30, 2014.