Gray stuff growing on trees? It’s Lichen!

Gray stuff growing on trees? It’s Lichen!


I receive questions from time to time that they have a tree or trees that are being killed by a grey substance growing on the tree or plant. What they are talking about is a combination plant that is part fungi and part algae. There are about 3600 known species of lichens in North America. They come in many colors and many growth forms.

The important thing to note here is they are not harmful to your trees or plants. I have lichen growing on my dogwoods, oaks, camellias and azaleas. Often lichen is found on older plants simply because the bark may be peeling or there may be a rotten spot that makes it easy for the lichen to attach to.

I have seen lichen growing on rock, especially brick, houses, etc. I even had some grow on one of my vehicles that I had been careless in washing. It had not harmed any of the spots mentioned, just looked bad in some places.

Lichens do not have any roots, stems or leaves. They attach to rough surfaces primarily. They do not remove moisture or nutrients from trees or plants.

Lichens are important for several reasons. One is their pure beauty. In the Northwest you find long strands, called witch’s hair, hanging from the branches of old firs and spruce. In the Rocky Mountains they make up the bright reds, yellows and green colors that you see on the cliffs. These are called crust lichens.

One direct benefit to humans is their ability to absorb everything in the atmosphere especially pollutants. They provide us with valuable information about the environment around us. Any heavy metals, carbon, sulfur or other pollutants in the atmosphere are absorbed into the lichen thallus. Scientists can extract these toxins and determine the levels that are present in the atmosphere.

Again, the important thing to remember is they do not harm the plants to which they are attached. Enjoy their beauty. Lastly they will outlive us or the plants to which they are attached.