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What's This Green Stuff Growing On Trees And Rocks?

May 7, 2020
Topics

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

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

What’s the difference between moss and lichen?

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 to the touch

Lichen:

  • 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.

What causes moss and lichen?

Just like any other plant, moss will grow if the environment is right. It thrives in shady, moist areas.

Lichens also sprout 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.

Does lichen grow on healthy trees?

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

Is lichen harmful to my trees?

Ok, moment of truth: does lichen kill trees? Nope! Lichen does 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 grow on, 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.

How to get rid of lichen on trees

To reiterate, lichen is completely harmless to trees, and there’s no real need to get rid of it. But some people don’t view lichen as one of “nature’s wonders,” and instead consider it a green fungus on trees.

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 Davey arborists 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. Here’s why.

Benefits of moss and lichen

Why yes, believe it or not, these green growths come with perks. Both are used as food for many animals, and as nesting for birds.

What’s the benefit for you? Well, since lichen seeks out stressed trees, it might be the reason you discover your tree is struggling. With that, you can take action to help your plant, thanks to lichen.

Read here for more on tree bark “fungus” identification.

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