The skiff of white stuff that greeted me when I stepped outside this morning can mean only one thing: it’s time to bring out the sweaters and warm woollen blankets that have been tucked away for months, and anticipate long evenings cuddled up with a good book in front of the fireplace. The first frosts have occurred, to be followed by the icy blasts of winter cold and snow that are so familiar to those of us residing on the Prairies.Have you ever thought about what plants go through during the freezing process? It’s not pretty! A light frost, the kind that leaves a thin film of ice on plant surfaces and burns off by mid-morning, usually results in foliage damage. Ice crystals build within the leaves, expanding and destroying the cells, which results in the tissue turning black or becoming “slimy,” then collapsing and dropping off. Any tender herbaceous plants (annuals, non-hardy perennials) that suffer widespread foliage damage die off quickly. A heavier frost that happens rapidly, over the span of mere hours, will be more catastrophic to plants: foliage will be destroyed, and the ice crystals will attack the twigs, stems and branches of both woody and herbaceous plants. Plants that are not sufficiently hardy are killed; this is why it is very important to plant according to the hardiness zones in your region. Tough perennials and roses may die back completely to the ground as their roots go dormant. Trees will undergo dormancy as well, and they will usually not suffer too much from the death of a few branches and twigs.
But that’s not the end of it – Calgary winters are known for their famous Chinooks, which can do staggering damage to frozen plants. The temporary warm spells cause the soil to partly thaw, only to freeze rapidly when cold weather returns. The soil heaves, disturbing dormant plant roots. Rapid thawing also expands the water in and around plant cells and can cause the wood and bark of tree trunks and branches to crack open. Furthermore, if the warm spell is prolonged, and snow cover is insufficient, plants may suffer further injury when tender new buds emerge and are subsequently destroyed by a fresh round of icy weather.
Then there are the other weather extremes of winter: freezing rain, drying winds, and heavy, wet snow, all capable of doing massive damage to your garden. Huge accumulations of snow don’t usually do any damage to low-growing plants – in fact, snow is the biggest asset to your garden in the winter, as it provides an insulating cover that helps to stabilize the root temperatures of plants at soil level, and offers protection against desiccation and vicious freeze and thaw cycles. Extremely heavy snow can be particularly damaging to large conifers, however, weighing down branches and causing breakage. Freezing rain can inflict even more severe punishment on large trees: the coat of ice on branches and trunks is deceptively weighty and can topple entire trees or ruin hedges. While snow usually falls off the leafless branches of deciduous trees, freezing rain will affect both deciduous trees and evergreens. Desiccation, particularly of conifers, is another issue Calgary gardeners face: prolonged cold and dry winds remove the beneficial snow blanket and may damage exposed conifers. Always give your trees a leg up before winter: water deeply in the fall, apply anti-desiccant sprays (if desired), and wrap or tent particularly vulnerable specimens. It is easy to see why winterizing the garden is so necessary!
I love Frank Ferragine’s “less is more” philosophy in Winterizing Your Garden – it’s exactly how I roll with my own gardening. Nora Bryan follows suit in Faded Glory, with some excellent tips on what and what not to cut, and how to use dried leaves as protective, insulating mulch for your dormant plants.
(The original version of this post first appeared in Calgary Gardening, October/November 2011. Thanks, Calgary Horticultural Society, for allowing me to reprint it!).