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TRISH DeHOND: Like it or not, lichens do no harm

May 26, 2019

To follow up on last week’s topic, we will take a closer look at some other “scaly things on trees that may not be what they seem.”

Over the past eight months, I have looked at several cases and heard from homeowners describing a scaly “mold,” usually gray or green, that is “killing their favorite tree” or shrub. This description fits many different kinds of lichens, which are very interesting organisms.

Pronounced “LIKE-en” (not “litch-en”), they are typically dry and scaly and have a mold-like or moss-like appearance growing on the trunks or branches of trees and shrubs, but also on rocks or soils.

Lichens actually contain cells of two different organisms, algae and fungi that grow together to form what appears to be one organism or body. The lichens that grow on trees or shrubs are typically gray, green or white and do not cause any harm to the plant.

They are just a sign of one or more of the following: old age, high humidity, plenty of sunshine, and poor growing conditions.

Just like wrinkles on people never killed anybody, they may be just a sign of TMB (“too many birthdays”). You may also see them on shade-loving plants, such as azaleas, when the tree or shrub canopy is thin and the plants are receiving too much light.

So, since the lichens are not killing your azaleas, you would just need to improve the growing conditions to improve plant health. I recently looked at some live oak trees that were declining for other reasons, and found a healthy crop of lichens growing on the trunk. This lichen growth is fairly normal, but when healthy trees grow, the bark is pushed aside into furrows, causing the lichens to break apart over time. So, a thick patch of lichens is a sure sign of very slow growth on tree trunks.

I also recently had a chance to visit the garden of Mary and Terry Thomas in Lydia, and was shown the most fascinating use of lichens that I have ever seen. Terry produced a hummingbird nest that he had found in the crotch of a fallen oak tree. The beautiful nest was lined with spider webs and feathers, and covered with a tile-like coating of bits of lichens. It looked like a very comfortable and well-camouflaged home for the baby hummers to grow up in.

To learn more about lichens (as well as Spanish moss and slime molds), please see our fact sheets at the Clemson Extension Home and Garden Information Center at https://hgic.clemson.edu/factsheet/spanish-moss-lichens-slime-molds/.

Trish DeHond is the Home Horticulture Agent and Master Gardener Coordinator for Clemson Extension in Darlington & Florence Counties. She can be reached by email at pdehond@clemson.edu. Clemson University Cooperative Extension Service offers its programs to people of all ages, regardless of race, color, gender, religion, national origin, disability, political beliefs, sexual orientation, gender identity, marital or family status and is an equal opportunity employer.

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