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Jul 14, 2015 | 376 views | 0 0 comments | 15 15 recommendations | email to a friend | print
Gardening 120 : Basics & Beyond

What is Growing on My Tree Bark?

For the last 10 years I have had the good fortune to live in a neighborhood with lots of big old trees, and I have quite a few of them in my own yard. Several of my trees appear to have a blotchy, pale green or grey, scaly growth on their bark, and I have often wondered just what that “stuff” is. As a master gardener intern, I feel this is something I should know, so I have done a little research, and now I want to share my findings with you!

The organism growing on my tree bark is known as lichen, and to my relief, it is not a signal that the tree is sick or dying, nor is it damaging the tree. Lichen is actually a combination of two or more different organisms that form a mutually beneficial relationship to produce a new vegetative body that is called a thallus. The lichen thallus is composed of a fungus and most often a green alga and/or a cyanobacterium.

Lichens are found on healthy trees as well as trees that are stressed or unhealthy. Since lichens need only sunlight, rainwater, and minerals from the air to survive and produce their own energy, they do not feed on the tree bark. If lichens are growing on a diseased tree, it is likely that there is another organism that is causing the disease or injury.

I was surprised to learn that lichens provide many benefits both in nature and in human culture. Animals such as deer, mountain goats and caribou use lichen as a food source, and some species of birds use lichen materials in constructing their nests. We humans use certain lichens to produce antibiotics, and other types of lichens provide the miniature plant landscape for model railroad tracks! I also found it interesting to learn that the presence of lichens on healthy trees indicates lower levels of air pollution and a reasonably good quality of atmospheric conditions in the neighborhood.

If you would like to learn more about the fascinating group of organisms known as lichens, you can refer to the Rutgers Fact Sheet FS1205, Tree-Dwelling Lichens, by George H. Daniel, Rutgers Master Gardener, Somerset County, and Nicholas Polanin, County Agent, Agriculture and Resource Management, Somerset County. It is available at the Extension Center or on-line at:

If you have any questions please feel free to contact the Rutgers Master Gardeners of Cumberland County through our telephone helpline at: 856-451-2800, ext. 4, or stop in and see us at the Cooperative Extension of Cumberland County, Rutgers New Jersey Agricultural Experiment Station, 291 Morton Ave., Deerfield Township.
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