Garden Column for the week of Jan. 6, 2006
By Cindy Haynes
Iowa State University Extension
I know – I know, nothing sounds more boring than tree bark. But, what in the landscape can you see and enjoy outside this time of year? The snow and evergreens are beautiful together, the stark architectural beauty of certain trees and shrubs is revealed after the leaves fall, and the dried foliage of many ornamental grasses and other perennials provides interest throughout the winter months. But a dominant feature of the winter landscape -- bark -- doesn’t receive much attention. In winter, without the presence of leaves, bark is easier to see and can be quite fascinating upon closer inspection.
What is bark and what is it good for?
Technically, bark consists of living and dead plant cells present at the periphery of plant stems. Bark is a distinctive characteristic of woody plant species and can be as unique to a tree as its leaves. However, bark has similar functions for most species. Given its position and makeup, the primary role of bark is protecting the inner living cells from fire, predators and other threats. Some species of trees, such as bur oak (Quercus macrocarpa), have bark that is particularly resistant to fire. Other trees have bark with thorns (Honeylocust or Gleditsia triacanthos) that protect the tree from animal attack.
In addition to protecting the tree, bark is used for many other purposes. In the rainforest, epiphytic plants like orchids use bark as an anchor for roots. Many animals and insects use bark as habitat or hiding places. We humans have used bark in a variety of ways for centuries.While today bark is used by homeowners primarily for mulching garden plants and paths, it was once used to make canoes, dyes and medicines. And don’t forget one of our favorite spices, cinnamon, is made from bark.
Bark is an interesting feature of the landscape.
One of my favorite trees for ornamental bark is sycamore (Platanus occidentalis). Sycamore bark has patches of green, gray, white and tan that are randomly put together like a scrappy quilt. In winter, the strikingly light-colored sycamore bark can be seen in a forest from quite a distance.
A similar patchwork combination of colors can also be found on the bark of older lacebark pines (Pinus bungeana). While it may require some effort to find this pine for sale in your area, you will be richly rewarded. Another pine with attractive bark is Scotch pine (Pinus sylvestris). The reddish-orange bark contrasts nicely with the dark evergreen needles. This pine is no longer recommended for planting in Iowa home landscapes, however, due to serious pest problems.
Black walnut (Juglans nigra) displays a coarse, deeply furrowed bark in the winter months. The gray ridges and black furrows are rugged looking and provide a stark textural contrast in the winter landscape. Other trees with deeply furrowed bark are many species of ash (Fraxinus) and Kentucky coffee tree (Gymnocladus dioicus).
Birches are known for their distinctive bark characteristics. White birch (Betula papyifera or B. pendula) has chalky white bark with occasional charcoal colored ridges for contrast. Unfortunately, white birch prefers cooler climates, where it suffers less damage from borers. For Iowa, river birch (Betula nigra) is a better and popular landscape choice. River birch has peeling cream, tan or pale peach colored bark. Trees are often sold with several trunks, making a more substantial impact in the landscape.
While walking in the woods, it is easy to recognize the flaky, gray strips of Shagbark hickory (Carya ovata) and white oak (Quecus alba). These Iowa natives are exceptional landscape trees for large spaces. Both provide interest throughout the seasons and are often long-lived in the landscape.
Many trees have a smooth bark character, but only a few are noted for it. European beech (Fagus sylvatica) has smooth gray bark and large trunks that resemble the skin of an elephant. Some cherries (Prunus) are also noted for their glossy, smooth reddish bark and horizontal lenticles. Paperbark maple (Acer griseum) has smooth cinnamon-colored bark that peels off in paper-sized sheets. Unfortunately, these trees perform best in protected locations in the southern half of Iowa.
A more cold hardy selection suitable for all of Iowa is Japanese Tree Lilac (Syringa reticulata). It has smooth reddish-brown bark. It is also smaller than many of the trees listed above, therefore, it can be planted closer to the house -- making it easier to view from your heated house! For smooth gray bark, consider hornbeam (Carpinus species), serviceberry (Amelanchier species) or some maples (Acer species).
These are just a few of the trees that I see and enjoy while walking the Iowa State University campus. While you are scurrying to and fro this winter season, glance at a few of the trees and shrubs you pass. The patterns, textures and colors of bark are worthy of a second look.