Brian Minter: Dealing with extreme weather patterns is becoming the norm

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After the extremes of 2021, nothing, in terms of weather, should surprise us in the year ahead. Even our recent cold spell has done some significant damage in our gardens … and there’s still a couple of months of winter to come.

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At this point, it’s a question of mitigating the damage the cold has already done, while at the same time, being better prepared for the next weather event. Depending on where you live, you can grow everything from semitropical palms to extremely hardy Arctic willows. Now, however, the changing climate, with more extreme weather patterns, is pushing the boundaries of both record cold and heat.

One important garden basic to understand is plant hardiness zones.

The cold hardiness and heat tolerance zones of North America were first laid out many years ago by the U.S. Department of Agriculture (USDA), with input from Canada and Mexico, to provide a reasonable sense of the various cold and heat zones of all three countries.

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On the whole, it’s been a very good indicator of average hot and cold temperatures for most locations. It’s not, however, an exact science because it cannot account for how microclimates in every region are influenced by topography, weather patterns and the effects of oceans, lakes, forests, hillsides and mountains.

Although this map is only a guide, by comparing it with the established zone hardiness of most plants, it will give us a good sense of a plant’s ability to grow well and survive in a specific region.

Plant hardiness is also a subjective issue, one based on history and a plant’s native habitat. Temperature is just one measure. The type of soil, average rainfall amounts, wind patterns, exposure to sun or shade are all contributing factors to a plant’s ability to not only survive but also thrive.

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Not all plants have been assigned accurate heat or cold tolerance zones; this is especially true for new introductions. Few countries in Europe use zones because it’s so difficult to fully address their weather tolerance. I used to jokingly ask European plant folks whether a certain plant would survive in the mountains of Scotland in order to get some sense of a plant’s comparative cold tolerance in Canada.

In general, if you know the hardiness zone in which you live, and you have a fairly good idea of a plant’s cold hardiness rating, then you should feel reasonably confident in making your plant selections. If you live in the eastern Fraser Valley, which is truly a zone 6 area, you can plant not only zone 6 plants but also those plants rated zone 1 through zone 5. Depending on your location, especially if you are situated out of winter’s northeasterly outflow winds, and can provide a little protection, you may be able to grow zone 7 plants. Also, once a plant becomes established, it develops more hardiness and is able to withstand colder temperatures than its zone would suggest.

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In dealing with the most recent record cold, we were fortunate to first have a snowfall which insulated and protected many plants. I worry, however, about the many tender plants, like palms, phormiums, Musa basjoo bananas and many other semi-hardy or zone 7 and 8 plants. Even with proper mulching, windbreaks and insulation, the length of time the penetrating cold lasted means some plants will be lost. In many cases, we will have to wait until spring’s warm weather to truly know what has survived. Sometimes when the frost comes out, the stems and roots will turn to mush, and you will know then for sure that the plant is gone.

Broadleaved plants, like camellias, rhododendrons, fatsias and ceanothus, when exposed to severe winds, may suffer burnt foliage and will look rather bedraggled, but they will recover when the new growth begins. It’s important to remember that camellias, and especially rhododendrons, have many different hardiness ratings.

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While most will tolerate a colder winter, others, especially those originating from warmer climates, may not make it. For example, PJM, a small leafed purple rhodo, will tolerate zone 4 conditions, while the large leaved bicolour Cherries ‘n’ Cream is really a zone 7 rhododendron. As a rule of thumb, smaller leaf rhododendrons are more sun and cold tolerant, and conversely, larger leaf varieties are less tolerant.

More and more modern roses, like the Easy Elegance series, are grown on their own roots instead of being budded. This gives them greater hardiness. If your roses are budded and the exposed buds were not mulched or protected, it’s possible they may be lost. Rose trees are especially vulnerable because their buds are two to four feet up in the cold air. Mulching them with bark mulch or sawdust or wrapping them with an insulating blanket, like N-Sulate, is a must before any winter cold spell.

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Container plants, too, are easily damaged by cold weather. When plants lose the protection of being in the ground and are exposed to the cold in containers, they are far more susceptible to frost damage. Plants lose at least one zone of hardiness when placed in a container. Containers need to be moved out of cold winds, and they need to be wrapped two to three times with an effective insulating material — like N-Sulate — rather than with burlap. Well-draining soil must be used in winter containers so they don’t retain excessive moisture that, when frozen, may cause ceramic or clay containers to crack.

Snow can be both a friend and an enemy. The weight of snow can pull apart hedging plants and break conifers, like bushy cryptomerias or spreading topiaries. To avoid broken stems or split plants, immediately after a heavy snowfall, especially if it’s wet snow, use a corn broom to gently knock off the snow.

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If your garden is exposed to the full force of outflow winter winds, creating windbreaks is essential. Wind chill factors can drop temperatures well below traditional hardiness zones. Erecting a simple screen of Remay cloth or plastic snow fencing can help save your plants and prevent wind burn damage on leaves or needles. Hedges also make wonderful screens.

Mother Nature is both kind and fierce. She is also a great teacher if we pay attention and observe. For both experienced and novice gardeners, this recent extreme cold spell will teach us to be better prepared for the next one. Never forget the lessons learned from lost or damaged plants.