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Have you seen moss growing on trees? Lichen is the term used for the blue green, papery growth that is often found on the bark of trees and other perennials. Sometimes folks are concerned over the growth of lichen, because they think it may be damaging their tree. Most of the time, this is not the case. Let’s talk about what lichens are, what causes them, and what you can do to control them, if necessary.

Lichens are really made up of a couple of different organisms. They usually will have fungus and algae. These organisms work together in a relationship that is mutually beneficial. Together these organisms produce the thallus, which is the leaf like growth that people see and recognize as lichen. Each organism has its own role in the relationship. The fungus provides a physical structure for growth, because the algae is slimy and has no structure. The fungus also provides water and minerals from the air or the material that the lichen is growing on. The algae are capable of photosynthesis, so they provide the carbohydrates needed for life. Some algae are also able to pull nitrogen from the atmosphere that the lichen need for development. Together they are able to combine and sustain life. 

Lichens grow all over the world. Different species will grow on different surfaces. For instance lichen that you see on a rock will not grow on a tree. Different colors are also possible. Lichen will begin to grow more on a plant if that plant has lost some of its leaves. When leaves fall from a tree, more sunlight is able to penetrate to the branches and trunk of the tree that will enable the growth of more lichen. Lichen is an opportunistic grower, meaning that healthy, actively growing plants will not have as much lichen on them. If there is an abundant amount of lichen on a plant that means there could be something that is stressing your plant, allowing the opportunistic lichen to grow. That could be a nutritional deficiency, a root disease, or an insect pest among other things.

Lichen does not kill plants. An abundant amount of lichen can be an indicator that something else is affecting the plant. Because lichen doesn’t damage plants, I don’t like to recommend products to kill it. You can remove lichen manually by gently scraping it from the bark. If you see a tree that has a lot of lichen growing on it carefully examine the plant. Here are some things to look for. Has the plant already lost its leaves? Are there holes in the bark from insects boring? Has the plant been receiving enough water? Are the roots turning black or are there mushrooms growing around the base of the tree? These are all questions that will help you determine if your plant is in decline and get to the root of the issue. 

If you have questions about lichen growing on your plants contact your County Extension Office or send me an email at [email protected].

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