We get a lot of questions about the gray-green, crusty or leafy growth covering the bark of Houston oaks and crape myrtles. That is lichen, a partnership between a fungus and an alga, and it is not a parasite. It simply uses the bark as a place to live and takes nothing from the tree.
Lichen does tell a story, though. It thrives in sunlight, so a sudden spread of lichen along the upper branches of a tree can mean the canopy above it has thinned and more light is reaching the bark. That thinning is worth a closer look, because it can come from root stress, drought damage from summer, or decline that is easier to address early.
Scrubbing or spraying lichen off the bark does nothing for the tree and can damage it. A better step is looking at the canopy, the root zone, and the tree's overall vigor, which is exactly what our certified arborists do on a consultation. Have you noticed lichen spreading on any of the trees in your yard lately?
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Real close-up photo of gray-green lichen on the bark of a Houston oak, ideally paired with a wide shot of the canopy above it. Avoid stock imagery.
Canva text suggestion: "Lichen Isn't the Problem, Look Up" or "What the Bark Tells You About the Canopy"