Wednesday, January 10, 2007

Bark with Bite

“Winter Interest in the Garden: Bark with Bite”

By Becke Davis

Seasons and that plants that are associated with them seem to have personalities much as people do. The plants and bulbs of spring seem warm and welcoming after the long winter, all yellows and pastels accented by the occasional spark of bright red tulips. Summer is all flash and show, with a rakish smile and boldly colored flowers from top to toe. Autumn is an old friend warming creaky bones by the fire, summer’s gaudy flowers replaced by a final curtain of foliage recalling all the colors on an artist’s palette.

Winter might be all silvery-gray elegance iced with frost, but there is still color in aspects of the landscape that catch the eye of discerning observers. The red of winter berries, yellow catkins, wheat-colored grasses, conifer needles of green, blue, gold and bronze, and newly visible bark and branches in shades of mahogany, nearly black and earthier browns, all foreshadowing the start of another cycle of the seasons in the landscape.

To those who look at nature and only see one shade of green, bark might appear somewhat boring and bland. On closer examination, though, bark is as distinctive as foliage and flowers and on some trees and shrubs, just as eye-catching. The paperbark maple (Acer griseum) is a case in point. While some large maples may be somewhat commonplace or even problematic, this distinguished tree has peeling, papery bark in colors ranging from orangey-brown to bronze to red or red-gold. Growing to 30 feet tall and a similar spread, the paperbark maple is an aristocratic specimen tree. It is hardy to zone 5 and performs well in full sun to part shade.

There are several maples with ornamental bark including the snakebark maple (Acer capillipes), trident maple (A. buergerianum), the David maple (A. davidii), Japanese maple cultivars including A. palmatum ‘Sango Kaku’, the striped maple (A. pensylvanicum ‘Erythrocladum’ and ‘White Tigress’) and the three-flower maple (A. triflorum). Other maples with interesting bark include A. mandschuricum, A. maximowiczianum, A. foresti ‘Alice’ and A. pseudoplatanus.

Many birches have ornamental bark, and the ‘Heritage’ river birch (Betula nigra ‘Heritage’) is one of the best. As the story goes, Earl Cully grew this tree from a cutting he requested from a tree he saw growing in someone’s yard. It is now a patented selection propagated by tissue-culture and rooted cuttings. Hardy in cold as well as hot climates, with variable fall color that can be an attractive yellow, this birch has much to recommend it but the peeling bark is what makes it a household name. The exfoliating bark is white and light tan to salmon-pink color on younger trees, changing to a tan to pinkish-brown as the tree matures.

The bark of white birch displayed against a backdrop of winter snow may seem one-dimensional, but snow cover is not consistent, and white birches are striking no matter what the backdrop. The bark of white birches has long been popular, but in recent years these trees have been viewed with caution because of significant problems including the bronze birch borer. Since white birches have long been beloved and valuable in the landscape, the result has been extensive research to develop or identify hardy and disease-resistant species and varieties.

A long term study comparing white birch species and varieties at the Morris Arboretum of the University of Pennsylvania in Philadelphia identified accessions of the Monarch birch (Betula maximowicziana) as the most promising. Native to Japan, this species features variable bark color ranging from white to creamy white or gray with black marks. Initially this species was thought to be borer resistant, although subsequent research leaves this conclusion in some doubt. A hybrid of Betula maximowicziana X B. papyrifera has displayed the most promising results. Another birch in this study that had a high survival rate was Betula populifolia ‘Whitespire Jr.’, grown from seed of a parent plant at Longenecker Gardens in Madison, WI. ‘Whitespire Sr.’ has also displayed resistance to borer infestation in this study. Other birches with ornamental bark include B. alleghaniensis, B. jaquemontii, B. lenta, B. pendula, B. platyphylla var. japonica and B. populifolia.

Other trees and shrubs with exfoliating bark or bark with a distinctive texture include cinnamon clethra (Clethra acuminata), yellow buckeye (Aesculus octandra), California incensecedar (Calocedrus decurrens, syn. Libocedrus decurrens), shagbark hickory (Carya ovata), ‘Winter King’ hawthorn (Crataegus viridis ‘Winter King’), Japanese cryptomeria (Crytopmeria japonica), dove tree (Davidia involucrata, hardy to zone 6), the corky-like burning bush (Euonymus alatus), seven-son flower (Heptacodium miconioides), oakleaf hydrangea (Hydrangea quercifolia), amur maackia (Maackia amurensis), dawn redwood (Metasequoia glyptostroboides), American hophornbeam (Ostrya virginiana), Persian parrotia (Parrotia persica), lacebark pine (Pinus bungeana), Japanese red pine (Pinus densiflora), London planetree (Platanus Xacerifolia), American sycamore (Platanus occidentalis), amur chokecherry (Amur maackii), Japanese flowering cherry (Prunus serrulata), Sargent cherry (Prunus sargentii), Japanese pussy willow (Salix chaenomeloides), black pussy willow (Salix gracilistyla ‘Melanostachys’), Japanese fantail willow (Salix sachalinensis ‘Sekka’), Stewartia spp. and Japanese tree maple (Syringa reticulata), hackberry (Celtis occidentalis), yellowwood (Cladrastis kentukea), quaking aspen (Populus tremuloides),

While some bark is attractive because of its texture, other bark stands out in winter because of its color. The redtwig dogwoods are extremely popular for landscape use, particularly those that have bright winter color. Examples include cultivars of the bloodtwig dogwood (Cornus sanguinea) ‘Viridissima’ and ‘Winter Flame’, the redosier dogwood (C. sericea) ‘Flaviramea’ (sometimes listed as ‘Lutea’), ‘Kelseyi’, ‘Silver and Gold’, ‘Cardinal’ and ‘Isanti’, Tatarian dogwood (C. alba) ‘Westonbirt’, ‘Sibirica’, ‘Spaethii’ and ‘Aurea’. The stems of Japanese kerria (Kerria japonica) are an attractive green while Rubus cockburnianus, R. phoenicolasius and R. thibetanus all have distinctly different colorful stems. The stems of Salix alba var. vitellina get progressively more colorful as the seasons change from fall to winter. Other willows with colorful stems include S. alba ‘Chermesina’ and S. alba ‘Britzensis’.

Trees and shrubs with colorful or exfoliating bark or bark with an interesting texture can keep a landscape from looking ghostly and stagnant in the long winter months. Careful pruning can enhance the effect of ornamental bark by opening up branching to make the bark more visible. Landscape lighting can also draw attention to attractive bark patterns. Next month’s feature will continue to address winter interest in the garden, with a focus on eye-catching or architectural plant forms.


Originally published in The Landscape Contractor magazine
(With thanks to Rick Reuland for the great, and non-alliterative, title!)

File Name: Barkwithbite.doc
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“Marvelous Midlevel Maples,” by Ed Lyon, American Nurseryman, March 1, 2005

“Twenty Years of Birch Evaluation at the Morris Arboretum,” by Anthony Aiello and Elinor I. Goff, Morris Arboretum, reprinted in Landscape Plant News, Volume 13, No. 4, 2002

“Betula Nigra Heritage,” by Rommy Lopat, The Weedpatch Gazette,

“A Perfect Fit,” by Reeser C. Manley, American Nurseryman, March 15, 1999

“Barking Up the Right Tree,” by Becke Davis, The Landscape Contractor, February 2001

Dirr’s Hardy Trees and Shrubs, by Michael A. Dirr, 1997, Timber Press, Portland, OR

Gardening with Foliage Plants: Leaf, Bark and Berry, by Ethne Clarke, 1997, Abbeville Press, New York, NY

The Year in Trees, by Kim E. Tripp and J.C. Raulston, 1995, Timber Press, Portland, OR

Landscaping with Native Trees, by Guy Sternberg and Jim Wilson, 1995, Chapters Publishing, Ltd., Shelburne, VT