The weight of accumulated layers of ice on frozen wood can cause branches to twist and snap, and is often referred to as nature’s way of pruning weak wood. (Photo by Joanne Young)
As we burrow under the bedclothes in a few months, let’s hope for a thick blanket of snow over the garden this winter. The structure of each snowflake contains layers of frozen water and air. As falling flakes pile up on the ground, more air is trapped within increasing layers of snow. This blanket of frozen water and air moderates winter soil temperature, keeping plant roots consistently cold, and preventing the heaving of roots out of the ground when exposed soil thaws in winter sunlight and freezes again in low night temperatures.
Small and newly installed clumps of perennials with shallow root balls are especially vulnerable to winter heaving. To help hold snow cover and keep roots in the soil, place branches from pruned shrubs and evergreens over plants after the ground has frozen. Snow will catch in the brush and provide a lasting winter blanket. (Branches cut from a discarded Christmas tree can be recycled for this purpose.)
No two snowflakes are alike and every snowfall is different. The ratio of frozen water and air contained within snowflakes is changeable, and weather conditions influence the weight of each flake. Snow containing more water than air is heavy, and hard to push or shovel. When heavy snow falls on evergreens, it causes the frozen branches to sag and bend, and they may break under the weight of the snow. If heavy snow is falling fast, monitor the accumulation on evergreens each hour. When accumulation on branches is one inch (2.5 cm) thick, use a rake or broom to gently knock the snow off. Frozen branches are brittle and easily broken, so it’s better to remove snow frequently throughout a snowstorm, rather than allowing it to accumulate.
And then, there is ice. A classic ice storm that coats limbs and trunks with glistening layers of ice is a beautiful sight, but also the source of much damage to trees and shrubs. The weight of accumulated layers of ice on frozen wood can cause branches to twist and snap, and is often referred to as nature’s way of pruning weak wood. There is little that can be done when ice coats tall woody plants, except to be mindful of the potential for damage that may need to be attended to in better weather. (If ice coats dormant flower buds during a cold snap, the ice may act as protective insulation against extreme low temperatures.)
Evergreens retain their foliage during winter, reducing water content in needles and concentrating their sugars and essential oils. (You may have noticed that evergreens have their best scent in winter.) However, they are still transpiring moisture during cold months, and accumulated ice may burn their foliage. Ice can be removed with a gentle nudge from a rake or broom; or for resistant ice, use your bare fingers to gently push it off, remembering that the frozen wood is brittle and won’t bear too much manipulation. Large sections of ice on evergreen branches can be loosened by a short blast from a hand-held hairdryer (on the lowest heat setting), using a long extension cord. If ice has splayed out and flattened sections of cedar shrubs, it’s best to leave them as they are; they usually rebound to their natural upright position in spring.
Soon it will be time to protect evergreens from winter stress. (Garden Making photo)
Despite the surprisingly warm days this week, it’s smart to consider what we can do to protect needle and broadleaf evergreen plants from winter injuries. Evergreen shrubs and trees might give the impression that they’re tough and resilient, but the truth is these plants require as much consideration as tender perennials, and need regular watering and an annual feeding to keep them in good condition. With good care through the growing season, they’re much better prepared to withstand severe winter cold. Regular watering during the growing season is the single most important factor in strong winter hardiness for all plants, including evergreens.
When plants are growing within their hardiness zone, cold air temperatures are unlikely to cause winter damage. However, the weight of crushing snow and ice is one hazard for coniferous shrubs; chronic exposure to extreme wind chill in exposed locations is another. When conifers accumulate large amounts of snow during winter storms, it’s worth getting out there with a broom to lightly push the accumulation off to reduce the weight on frozen branches. This is easy to do by putting the flat side of a broom on the underside of branches and gently bouncing them upward to dislodge snow. Never press downward on branches, as they are brittle and easily snap when frozen.
Where conifers are constantly buffeted by winter wind, a windbreak will offer significant protection. A living windbreak of trees, such as spruce and juniper, are better able to withstand the blast, and can form a shelter belt for more susceptible evergreen species. A more immediate and still reliable solution is to tie evergreen branches and discarded Christmas trees to the exposed sides of evergreens susceptible to wind damage, providing them with some insulation.
By far the most common winter injury is desiccated foliage (the loss of internal moisture in foliage tissues) on plants growing in locations with exposure to south and southwest sunlight and wind. Evergreens with lots of black or brown dead spots in spring have most likely been exposed to strong winter sunlight, sufficiently warm for a few hours at midday to stimulate biological activity in foliage and in the cambium layer under the bark. When the sun goes down, air temperature rapidly drops and tender tissues are caught in a sudden deep freeze. With a frozen root system unable to pump water, tissue death and split bark are the resulting injuries. This process of quick warming and sudden freezing is repeated every sunny day, and consequently damage to plants can be severe.
Yew, cedar and hemlock, and broadleaf evergreens such as boxwood and rhododendrons are most susceptible to desiccation. Anti-desiccant sprays provide a protective waxy coating and can be applied in late autumn. These aren’t entirely effective, sometimes flaking off before winter is over. The best solution is to provide shade from direct sunlight on foliage and bark by erecting a shade barrier with stakes and burlap. Surround the plant on three or four sides, without letting the burlap touch the branches, and without covering the top. Wrapping plants tightly in burlap will cause more problems by cutting off circulation and compressing frozen branches.
Protect tree trunks in late autumn by wrapping them with any light-coloured material or reflective wrap (available at garden centres). Remove wrappings in late spring. The idea is to keep plants cold and shaded, so foliage will remain dormant and inactive.
It’s a good feeling to know vulnerable plants are suited up and ready for their winter exposure. Needless to say, the gardener should be well wrapped and parked by a toasty fire for the duration.
Choosing conifer trees is a big deal. They’re expensive, permanent (hopefully) and they take up a lot of garden real estate. It’s no wonder new gardeners (and maybe not just new gardeners!) start to get nervous when making their choice. If not for this ongoing gardening education of mine, I would have never realized how many different sizes, colours and shapes of conifers there are.
Experienced gardeners take some knowledge for granted. (“You water the container when all the soil is dry, silly!” Or, “I’m sorry to disappoint, but there aren’t any perennials that bloom from spring to fall.”) Knowing how fast a tree grows and how to plant it may be information that others take for granted, but new gardeners have no clue about trees.
Our native white cedar (Thuja occidentalis). Photo from Humber Nurseries.
However, many beginner gardeners (but probably not enough) do know how important and valuable trees are. They offer shade, privacy, shelter for critters and a little hint of the majestic. To find out how to choose and plant conifers, I approached Darren Heimbecker at Whistling Gardens in Wilsonville, Ont., and JR Peters at Humber Nurseries in Brampton, Ont., with some beginner, and possibly obvious, questions. Part of my blog’s mission is to ask rooky questions. Sometimes I think I’m gaining a reputation at gardening companies and nurseries for dumb questions, but they took mine in stride.
I asked Darren and JR to recommend large, attractive, low-maintenance trees that grow quickly. Darren had lots of recommendations, (see below,) while JR had one particular favourite. For the best all-around conifer tree, JR suggested our native white cedar (Thuja occidentalis). It’s hardy to Zone 2, adapts to most conditions and is relatively problem free. It grows approximately 39 feet (12 m) tall and 7 feet (2 m) wide. Native trees are always a good choice, because they’re adapted to our growing conditions and climate.
If you’re looking for something a bit more unusual, or want more choices before making the big decision, here are Darren’s recommendations:
1) Lebanon cedar (Cedrus libani ssp. stenocoma): Growth rate of 20 inches (50 cm) a year. Height 60 feet (18 m) and width 20 feet (6 m). Hardy to Zone 5. It has blue/green needles (not unlike larches), but it doesn’t drop its needles.
2) Dawn redwood (Metasequoia glyptostroboides and cvs.): Fast growth rate of 2 to 3 feet (60 to 90 cm) a year. Height 60 feet (18 m) and width 15 feet (4.5 m). Hardy to Zone 4b. It has beautiful fall colours of oranges and russets.
‘Gold Rush’ — Brilliant yellow all season.
‘Gold Rush’ dawn redwood. Photo from Whistling Gardens.
‘Kool’s Gold’ — A new cultivar that’s even brighter yellow.
‘Silhouette’ — Gold and green needles.
‘Waasland’ — Somewhat more narrow and formal looking.
3) Norway spruce (Picea abies and cvs.): Growth rate of 1 foot (30 cm)+ a year. Height 30 feet (9 m) and width 12 feet (3.5 m). Hardy to Zone 4.
Aureospicata — New growth is brilliant yellow that matures to dark green.
‘Rubra Spicata’ — New growth is deep red that matures to dark green.
4) Blue spruce (Picea pungens and cvs.): Growth rate of 1 foot (30.5 cm) a year. Height 40 feet (12 m) and width 20 feet (6 m). Hardy to Zone 2.
‘Gebelles Golden Spring’ — New growth is brilliant yellow that matures to rich green.
‘Spring Blast’ — New growth is white that matures to cobalt blue.
5) Limber pine (Pinus flexilis and cvs.): Hardy to Zone 4.
‘Vanderwolf’s Pyramid’ — Growth rate of 1.5 feet (45 cm) a year. Height 30 feet (9 m) and width 12 feet (3.5 m). It has a dense form with green and silver colouring.
‘Extra Blue’ — Growth rate of 1 foot (30 cm) a year. Height 30 feet (9 m) and width 12 feet (3.5m). Has pretty blue-grey colouring on the needles year-round.
6) Korean pine (Pinus koraiensis and cvs.): Darren especially likes ‘Oculus-Draconis’, ‘Silveray’, and ‘Morris Blue’. Growth rate of about 1 foot (30 cm) a year. All grow to about 30 feet (9 m) or taller and 12 feet (3.5 m) wide. Hardy to Zone 4. They have 6- to 8-inch (15- to 20-cm) beautiful silver, blue and green needles. Cones are highly ornamental and stay on the plants for several years. They’re all dense growing, making them a good choice for a windbreak as well as shelter for birds.
7) ‘Zebrina Extra Gold’ Western red cedar (Thuja plicata ‘Zebrina Extra Gold’): Growth rate of 2 feet (60 cm) a year. Height 30 feet (9 m) and width 8 feet (2.5 m). Hardy to Zone 5. Beautiful rich gold variegated foliage.
I also asked Darren and JR what size tree people (perhaps slightly impatient gardeners) should buy if they’re looking for something to fill a large space right away. Darren suggested a 5-foot (1.5 m) tree as a good option because it has a visual impact right away. JR told me that the largest size you can buy at Humber Nurseries (and likely other nurseries, as well) is 10 feet (3 m). However, if the gardener has a bit more patience, 3-, 5-, and 7-gallon size pots are more affordable. The smallest size you could find in most nurseries is a sapling at almost 3 feet (90 cm) tall.
Of course, every species of tree will have different requirements and preferences when it comes to planting, but I asked for some basic tips from JR and Darren. JR told me that conifers can generally be planted at any time of the year, as long as the ground isn’t frozen. Darren said his favourite times to plant conifers are the early spring and fall, with September being his number one choice. This is because the trees will be able to root for about eight weeks before the ground is frozen.
Conifer trees like rich, moist, well-drained soil. Keep them well watered the first year or two, until they get established. If Mother Nature isn’t being helpful, give them a good soaking once a week — three or four buckets of water, depending on the size of the rootball, should be about right.
When deciding where to plant your new tree, leave enough room for its full width when it matures. Conifers are rarely pruned, so make sure it can spread out on all sides and not block windows or paths. The size of the planting hole depends on the size of the tree’s root ball. Dig a hole twice as wide as its diameter and no more than a few inches deeper than the height of the root ball. When planted, the top of the root ball should be at ground level or a tiny bit higher. For more tips, check out Garden Making’s article on how to plant a tree.
Choosing a tree can be one of the first landscaping decisions a new homeowner makes, but whether you’re designing a new garden or imagining the hidden potential of your current backyard, hopefully you’ll be able to find the tree that gives you the size, shade, privacy and colour you want, and will fit your garden perfectly.