Tree Lichens: What Are They?

What’s This Green Stuff On My Tree?

Shades of green can be spotted all around your yard; from lawns to leaves, to vines and herb gardens.

While tree trunks and branches aren’t typically a place you expect to see shades of green, that’s exactly what happens when lichen or moss pops up.

You might assume green spots on tree bark are a sign of trouble, but below, let’s get into the real story behind moss or lichen on trees. At Dr. Trees Oregon City, we actually encourage you to keep lichen around.

Moss Vs. Lichen

There’s actually a couple of things. For starters, they’re not the same organism. And, they look and feel quite different.

Moss Is:

  • A flowerless plant
  • Dark green in color
  • Coarse texture

Lichens Are:

  • Is a partnership between fungi and algae
  • Comes in a variety of colors (blue-green, gray and more)
  • Grows in as thin, flaky patches
  • Lastly, moss and lichen prefer different growing spots. You’ll likely only find moss on tree trunks and maybe rocks. But lichen will latch on to nearly any surface, including trees, other wood, rocks, cement or metal.

Causes Of Moss And Lichen

Just like any other plant, moss will grow if the conditions are right. It thrives in dark, moist areas, such as the underside of branches or the south face of a tree.

Lichens also grow wherever the conditions are in their favor. They love moisture, and they need light to thrive, so they’ll cling to tree trunks in areas with dampness and some sunlight.

Do Lichens Grow On Healthy Trees?

It does, but it’s much more common for lichen to appear on diseased or weak trees. The reason being, trees that are stressed or declining usually have a thinner canopy. Fewer leaves and branches mean more light shining on the tree trunk, and again, that’s precisely what lichens need to grow.

Are Lichens Harmful?

Ok, moment of truth: does lichen kill trees? The answer is….. no! Lichens do not pose a threat to your tree’s health.

Sometimes it appears that lichen is hurting your tree because it grows at the same time your tree is declining. But the reality is, lichen is an opportunistic organism just looking for a surface to latch on to, and unhealthy trees happen to be a good option. So, no need to worry about lichen harming your tree, but you should reach out to a professional arborist if you have other concerns about tree health.

Lichen Removal

We say again, lichen is completely harmless to trees, and there’s no real reason to get rid of it. But some people just see lichens as some sort of fungus that needs to be removed.

If that’s the case for you, you can use a copper-sulfate fungicide to kill lichen. Then, discourage future growth by keeping your tree properly pruned and in good health.

One question we sometimes get is: Can I use a pressure washer to clean or spray trees and get rid of lichen? It’s best to not use this powerful tool on trees. The pressure can damage the bark of your tree, exposing it to infections and disease.

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