Bark with Bite

Article by Michael Rosen
Images copyright Arlene Neilson
Image of P. cistena copyright M. Rosen

Extra-terrestrials viewing Canadian gardeners with time-lapse photography must be having a hoot! Earthlings slavishly preparing planting beds, transporting soil, dividing and transplanting plants, pruning, weeding, clipping, watering, flicking, spraying, weeding, weeding and more weeding, all within an intense, five-month period.

The rest of the year, from October to April, we probably would seem to be doing two things: raking leaves and quickly scurrying from vehicle to front door to escape winter’s fury. For many of us, our interest in our gardens stops with the frost. As the hostas turn brown, the shasta daisies lose their petals, and the coneflowers fall over, our interest in the garden reverts to "cleaning up" and hoping for a quick return to spring.

What we fail (or refuse!) to recognize is that our gardens are in a leafless, "winter" condition for at least seven months of the year! Failure to plan and plant for this can make for a dull, dull garden.

Fortunately, there is a cure. It lies in your choice and use of trees to brighten up the winter landscap — not for their leaves of course, but for their bark, twigs, and (sometimes) fruit texture and colour.

Deciding on the type of tree is another matter. Almost any tree’s bark can be considered interesting but some are definitely more interesting than others. Inevitably, tree choice depends on a number of key factors: soil type, amount of growing space, light conditions (shade vs. full sun), and last but not least, your desired look. This last criteria, being the most subjective, is subject to a number of factors:

• Conifers in general have interesting bark. Those that are evergreen (pine, spruce, fir, etc.) will look essentially the same in winter as they do in summer — green! The essential difference is that they will stand out much more in the winter.
• Contrast with your house colour should be a consideration, although not a dominant one. If your house is white, consider a red- or black-barked tree; if your house is red, you may want to consider something lighter in colour.
  All trees, especially the dark-barked ones, will stand out well against the white snows of winter.
• Different trees have different shapes (conical, rounded, flat-topped, etc.).
• As in all perennial choices, knowledge of plant hardiness zones is important (although there always are some trees that can survive outside of their zones). Plant hardiness is the ability of a species to survive in a particular climatic area.
• Canada has a great range of hardiness zones. Ontario alone has a diversity unparalleled in most countries. From Zone 6a in Windsor to Zone 0a in Fort Severn, or, as some put it, from Prickly Pear (Cactus) to Polar Bear! A version of the plant hardiness map exists on the Agriculture Canada Web site.

People should also start asking questions at their nurseries about seed zones. That is, whether the trees they are buying originate from seed collected from the area into which they will be planted. This can have tremendous importance for growth, survival, and genetic conservation. A map of Ontario's tree seed zones can be found on the Ontario Forests section of the Ontario Ministry of Natural Resources Web site.

The following is a look at some good, deciduous tree types for winter interest, the conditions they need to grow, and some appropriate comments:

Hackberry (Celtis occidentalis). A characteristically chestnut brown, curly bark that resembles cork. It is the latest rage in urban tree planting because it tolerates pollution, salt, and compacted soils and (loosely) resembles the once-great American elm. Tolerates all light conditions except for deep shade. Grows large, although one cultivar — "Delta", taken from near Lake Manitoba — is much more oval in crown form. Good to Zone 4.

Birches — White birch (Betula papyrifera) has a characteristic papery bark — always of great interest to people. It can grow on a wide variety of soils, cannot tolerate shade, and is good to Zone 2. Cultivars include "Chickadee" and, as a non-native substitute, European (or weeping) birch (Betula pendula), which is excellent for space-restricted lots. However, as popular as it is, the white birch is tremendously prone to insects, including birch leaf miner and bronze birch borer. Yellow birch (Betula lutea) on the other hand has an interesting, deep yellow, curled bark that makes it an excellent winter choice. It grows slowly, but to a large size in all but deep shade. However, it needs rich, moist bottomland soil, high in organic matter to allow for good growth. Good to Zone 3.

Cherries — Most species of cherry have an interesting, reddish bark with conspicuous horizontal lines (lenticels), attractive spring flowers, and summer fruit. These include the shrub pin cherry (Prunus pensylvanica) and the large, attractive tree, black cherry (Prunus serotina or "b.c.” — burnt cornflakes, which its bark resembles). Other non-native trees of interest include cherry plum (Prunus cerasifera), of which a cross called purpleleaf sand cherry (Prunus x cistena) has proven to be quite popular with gardeners because of its reddish-purple foliage. All cherries, however, are prone to a number of diseases, including black knot canker and dieback. They grow best in full sun. Good to Zone 3.

Beeches — The bark of the beech (sometimes called the “elephant tree”) is well known (unfortunately by graffiti writers) for its smooth appearance. This, its form, and pointy buds frequently give it its reputation as the classic tree of character. Both types — the native, American beech (Fagus grandifolia) and non-native European beech (Fagus sylvatica) — are slow-growing and known for their ability to grow in intense shade. The European beech has a large number of cultivars, including "Purpurea" ( the purpleleaf beech), "Aurea Pendula" (the weeping beech), and "Fastigiata" ( an upright beech of limited spread). American beech is good to Zone 4, European to Zone 5.

Dogwood — A shrub or small tree with very distinctive bright red twigs, dogwoods are a preferred landscaping species due to their hardy growth, attractive white flowers, and berry-like fruits. The most commonly planted species are alternate-leaved dogwood (Cornus alternifolia), which is hardy to Zone 3, and eastern flowering dogwood (Cornus florida), an understory tree (meaning tolerant of shade), which is only really hardy to Zone 6.

Ironwood (Ostrya virginiana) — The flaky, grayish-brown bark of this slow-growing, but attractive, medium-sized tree is not very well known to gardeners or landscapers. It can grow in intense shade on well-drained soils. The fruit clusters are retained and fall throughout the winter. Good to Zone 4.

Kentucky Coffee-tree (Gymnocladus dioicus) — A very underutilized yet interesting tree, due to its rough, scaly-ridged, unique, dark brown bark and long (up to 22 cm) pod, which forms in July, ripens in October, and hangs on the tree throughout the winter. The Kentucky Coffee-tree is also considered "threatened" in Ontario so planting it will help its recovery. It prefers bottomland (rich and moist) soils, does not tolerate shade, grows relatively fast, and forms attractive whitish flowers and attractive, doubly-compound leaves. Good only to Zone 5.

Editor’s Note:

In western Canada you should also consider the following trees:

Arbutus (Arbutus menziesii) — a distinctive tree with reddish-brown bark that peels off in papery curls; native to southeastern Vancouver Island and the Gulf Islands, and scattered along the southern mainland BC coast
Garry oak (Quercus garryana) — a tree of character with grey-brown bark full of ridges and furrows; native to the southern southern tip of Vancouver Island and north along the eastern coast to the Comox area
Western flowering dogwood (Cornus nuttallii) — a beautiful small tree similar to the eastern flowering dogwood; native to Vancouver Island and mainland BC coastal areas into the Fraser Canyon
Bitter cherry (Prunus emarginata) — another cherry for consideration that is found across southern BC to subalpine areas.