What’s in a Lichen?

Take a close look at the trunk and branches on a tree in your yard. There is likely something growing on it. It’s easy to assume that this thing must not be good. If something is growing on my tree, it must be harming it, right?

I frequently get asked about the blue-green flackery stuff growing on trees. What is it? What should be done?

This “stuff” is usually lichen. It’s two organisms that live together. The flaky material is a fungus. It establishes itself on tree bark, absorbs water when available, and provides a home for algae. The color comes from algae (similar to the algae found in warm standing water). The algae gathers sunlight and provides food for the fungus. This is a symbiotic relationship: The algae and the fungus rely on each other to live. The tree is just a place for lichen to grow. It does not harm, or benefit the tree.

Lichen can give you clues about its environment. They don’t grow well in high ozone environments and don’t not like acid precipitation. So, their presence is a positive indicator of air quality. Lichen can increase in growth if there is an increase in filtered light. An increase in lichen can give a clue that a tree is thinning and has other issues. 

If you don’t like the look of lichen, you can get rid of it; though it is not recommended. Remember, lichen is neither harmful nor beneficial to the tree.  A copper-based fungicide can kill it, but this may be harmful to other fungi, some of which are beneficial to the tree. It would likely be better to leave it alone, take a close look at this strange living thing, and see it as an interesting addition to your landscape.