Lee Valley & Veritas

 Gardening Newsletter
 
  Volume 8, Issue 10 - October 2013    
 
The Beauty of Bark
Peeling birch bark cherry tree
The peeling bark of a birch bark cherry tree reveals the trunk's rich mahogany-red color.
 
All gardeners know that blossoms, even the longest lasting ones, are fleeting. Are you able to look beyond the flowers? There is a lot of hidden beauty to be discovered. Behind the blooms and the foliage, there's bark — a constant garden feature that is beautiful in its own right.

Bark, the outermost tissue found on all woody plants, serves several functions. It protects against weather elements (temperature extremes or intense sunlight), defends against insect, bacterial and fungal infestations, helps to slow water loss, and enables the tree to breathe via lenticels.

New bark is usually thin and smooth. As it ages, layers of old dead cells build up causing the bark to thicken. Some trees, such as American beech (Fagus grandifolia), have bark that is extremely pliable and remains amazingly smooth even on mature specimens. The bark of the majority of trees and shrubs, however, has limited expansion capability. As their trunks grow, the older outer bark ruptures in various ways, altering its look. It sometimes leaves behind patterns (stripes or diamonds) or a chunky or patchy appearance. On certain species, it can cause flaking or peeling that reveals the inner bark. Bark texture becomes more distinct and beautiful as the tree or shrub matures.

 
Striped maple   Père David's Maple   Oregon grape
Striped maple   Père David's Maple   Oregon holly grape
 
Many maples develop bark with attractive long vertical splits that are highlighted by the color differences between the new and old bark. Examples include the striped maple (Acer pensylvanicum) and the Père David's maple (A. davidii). The bark of the red snakebark maple (A. capillipes) is quite striking, with its green and white diamond pattern that resembles snakeskin. The mature stems of the Oregon holly grape (Mahonia spp.) display attractive bark broken into geometrically regular fragments. The champion of regular diamond patterns, however, is definitely the bark of the white ash (Fraxinus americana), which breaks into thin, intersecting ridges.
 
Sargent crabapple tree
The scaly bark of the Sargent crabapple tree adds great texture to the garden.
 
Tree bark sometimes shatters due to trunk expansion. The loose pieces flake off, producing a rough texture. Hawthorn (Crataegus spp.) and American hophornbeam (Ostrya virginiana) bark breaks into small but firm shreds that loosen with age. Similar textures can be found on many fruit trees such as Sargent crabapples (Malus sargentii), which produce rectangular brown-gray scales. The ponderosa pine (Pinus ponderosa) has orangey-brown bark that fissures into large, flat, flaky plates. Trident maple (A. buergerianum) bark develops plate-sized flaky scales, which is quite pretty.
 
Paperbark maple   Japanese stewartia
Paperbark maple   Japanese stewartia
 
Another of nature's hidden beauties is the group of trees with bark that peels to reveal wonderful colors. The bark of paperbark maple (A. griseum) is an appealing cinnamon shade. Sometimes trees have both lovely colored bark and inner wood that boasts attractive color, such as the mahogany-red trunk of the birch bark cherry (Prunus serrula) and the silvery-green inner wood of the arbutus (Arbutus menziesii). The common ninebark shrub (Physocarpus opulifolius) has distinctive reddish-brown bark that peels to reveal light-colored inner wood. Occasionally trees apply two different strategies. The Scots pine (P. sylvestris) has smooth bark on its upper section that peels in papery strips, while its lower section has bark that is deeply fissured into irregular, loose, scaly plates.
 
Common ninebark   Persian ironwood
Common ninebark   Persian ironwood
 
Bark can break into irregular pieces due to expansion, giving the trunk a multi-colored patchy appearance. A great example of this effect is the stewartia. Others include the plane tree (Platanus spp.), with brown bark and white inner layers, the Persian ironwood (Parrotia persica), with tri-colored patches, and the quince (Cydonia oblonga), with a multi-colored trunk.
 
Himalayan birch   Red dogwood before a white birch
Himalayan birch   Red dogwood before a white birch
 
Tree bark varies in color from white to yellow, orange, red and all imaginable shades of brown and black. It is typically brown due to tannins; the fewer the tannins, the lighter the bark. The best known genus with light-colored bark is birches (Betula spp.). Of all the trees with white bark, the Himalayan birch (B. utilis var. jacquemontii) is considered the most attractive. Not all birches have creamy-white-colored bark, though. Sweet birch (B. lenta) has brownish-black and river birch's (B. nigra) is a grayish-brown color. Striking red bark is found on some Japanese maples, such as the coral bark maple (A. palmatum 'Sango-kaku'). Many shrubs in the dogwood family also feature red bark. Examples include the tatarian dogwood (Cornus alba) and the red osier dogwood (C. sericea). The exception is cultivars such as 'Flaviramea', which has honey-yellow bark. Both colors are highlights in the snowy winter garden.
 
Horizontal lenticels
Horizontal lenticels are visible on the bark of a young katsura tree
 
Occasionally, what makes bark so attractive is what you find growing on it. Lenticels act as breathing pores, permitting gas exchange between the interior of a plant and the atmosphere. On younger trees, they are often visible as small bumps on the bark, while on older trees, they're hidden in the bark fissures. In birch and cherry trees, lenticels can be quite ornamental, forming conspicuous, differently colored horizontal lines. On elders (Sambucus spp.), prominent lenticels appear as wart-like spots and although interesting, they can't really be called ornamental. Other mature trees, particularly maples, attract plants (harmless mosses and lichens, for example) that grow on top of the bark. Large plant-covered trees create a spooky year-round Halloween-like scene.
 
Moss covered Japanese maple
The moss-covered branches of a Japanese maple
 
Interestingly, the inner bark of a few trees contains olfactory wonders. Certain true cedars such as the atlas (Cedrus atlantica), deodar (C. deodara), Lebanon (C. libani) and Cyprus (C. brevifolia) emit a spicy aroma somewhat similar to that of the sassafras tree (Sassafras albidum). Emitting a sweet fragrance is a specialty of two birches, the sweet birch (B. lenta) and the yellow birch (B. lutea). Conversely, the bark of the black cherry (P. serotina) is known for its bitter almond aroma.

This winter, while you are poring over plant catalogs, consider that many trees and shrubs have a lot to offer beyond just a few weeks of flowers. Remember, there is beauty beyond the bloom — you just have to look carefully.

Gina Dobrodzicka

 
Moss covered Japanese maple
The same tree as above. You can see that almost all of the bark is covered with moss.
Gina Dobrodzicka is a freelance writer and trained horticulturalist who volunteered with Master Gardeners of Ottawa-Carleton for five years. Currently, she volunteers with the Vancouver Master Gardeners Chapter, the South Surrey Garden Club and Darts Hill Garden Society. She recently re-established her landscaping company. Her website is www.gdgardendesign.com.
 
 
 
     
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