- March 30, 2016 - Jardin botanique : Horticultural news
Dandelions blooming in December? It actually happened this past year! And this decidedly odd occurrence is just one example of how wacky our seasons have become in recent years. We’ve had winters with extreme cold or warm spells, early springs with late frosts, and long, dry falls. It all seems to have become the norm here in Quebec. How are these unexpected changes affecting our gardens?
Let’s start by taking a look at their impact.
Completely off kilter
Changes in the timing and length of the seasons are nothing new. Horticulturists have noticed that our climate has been warming and the seasons fluctuating from one year to the next for some time now. You want proof? The latest plant hardiness zone map published by Natural Resources Canada, based on data compiled over a roughly 30-year period, clearly shows that all of Quebec has shifted by almost a full zone. Such changes may eventually alter the characteristics of these ecosystems, leaving our native plants unable to adapt quickly enough to survive.
Early, unpredictable springs
Early springs often mean warm spells that encourage plants to bloom sooner than usual. Leaves and buds open earlier, when there is still a risk of a late frost, more and more common in April and May. Although most early bloomers can tolerate temperatures a few degrees below zero even when in full bloom, the mercury can sometimes fall too far. It is no longer unheard of for temperatures to swing between -20°C and +20°C during this period, killing all young leaves and blossoms. The plant will produce new buds, but these repeated traumas make it more vulnerable. Trees with thin bark also feel the effect of such temperature fluctuations, as the bark splits and literally peels off. This makes it hard for the sap to circulate, and entire parts of branches can die. The weakened tree is more susceptible to possibly fatal diseases and insect pests.
Long, dry falls
Falls in Quebec used to be cool and damp, but these days are more commonly warm and dry, and followed by suddenly plunging temperatures. We humans enjoy the fine weather, but it’s a different story for plants. They need to chill gradually to prepare for the coming harsh winter. Our overly mild fall weather prevents plants from hardening off. Unprepared, they have trouble surviving the winter. And since they normally stock up on water in the fall, the long dry spells that have become common prevent them from storing enough water to get through the winter. Their reserves evaporate – an especially common problem for conifers – making it hard for them to withstand the extreme temperature swings that are now a feature of our winters.
To be continued...