Lichen on Tree Bark: Harmless Growth or Warning Sign?

Every few weeks somebody in Edgewater or Port Orange calls about a "fungus" spreading over the bark of their oak or crepe myrtle. Gray-green, sometimes pale blue, sometimes orange, in flat crusts or leafy little ruffles. That is lichen, and it is one of the most misunderstood things on a Florida tree.

The short version: lichen does not harm trees. But heavy lichen on a tree that used to have little can tell you something about the tree, and it is worth understanding what.

What lichen actually is

Lichen is a partnership between a fungus and an alga (or cyanobacterium). The fungus provides structure and the alga makes food from sunlight. The result is an organism that grows on rocks, fences, roofs and bark, taking nothing from the surface it sits on. It has no roots, and it does not penetrate bark or draw sap.

Lichen also needs clean air to thrive. Heavy lichen growth is, if anything, a sign that the air on your lot is decent.

Why it shows up more on some trees

Lichen needs light and moisture. On a vigorous tree with a full canopy, the trunk and limbs are shaded, the bark is expanding as the tree grows, and lichen has a hard time getting established. On a tree that is slowing down, the canopy thins, more light reaches the bark, the bark stops expanding, and lichen has a stable, sunlit surface to colonize.

So the correlation people notice is real: declining trees often carry a lot of lichen. The lichen is a passenger, not the driver. It is on the tree because the tree slowed down, not the other way around.

The same logic applies to Spanish moss and ball moss, as we covered in Spanish Moss and Ball Moss on Your Trees.

When lichen means you should look closer

If a tree has always had lichen on the trunk and looks healthy, ignore it. If lichen has spread noticeably over a season or two, and especially if you also see:

• Thinning at the top of the crown
• Smaller leaves than usual
• Dead tips on the outer branches
• Sparse new growth in spring
• Mushrooms at the base

then the lichen is confirming what the crown is already telling you. The question is what is stressing the tree, and that usually comes down to roots: compaction, a grade change, trenching, a buried flare, or chronic drought or salt. Our post on drought stress vs. overwatering is a good starting point, and compacted soil is the most common cause we find.

Lichen on crepe myrtles and citrus

Crepe myrtles and citrus in our area often carry heavy lichen on twigs and small branches, sometimes enough to make people think the twigs are dead. Scratch the bark. Green underneath means alive.

On citrus specifically, lichen tends to pile up on trees that have been in decline from greening for a while. The lichen is not the problem; the disease is. See our post on citrus greening for an honest look at what can be done.

Should you remove it?

There is no benefit to the tree in removing lichen, and scrubbing or scraping bark can wound it. Copper-based fungicides will kill lichen, and some people spray crepe myrtles for cosmetic reasons, but the lichen comes back if the conditions that favored it remain. We do not recommend treating lichen. Treat the reason the tree slowed down.

What we do instead

When a client calls about lichen, the site visit is about the tree, not the lichen. We look at the root flare, the soil, the canopy density and the growth from the last few seasons. If the tree is fine, we say so and leave. If it is not, the fixes are things like excavating a buried root collar, decompacting the root zone, correcting mulch and irrigation, or removing deadwood so the tree can put its energy into the parts still working.

Frequently asked questions

Is lichen the same as mold or mildew?

No. Mold and mildew are fungi that grow on damp surfaces and on leaf tissue. Lichen is a stable organism that grows slowly on bark and does not need the surface to be wet all the time. Sooty mold, the black film that grows on honeydew from insects, is a different thing entirely.

Does lichen mean my tree is dying?

By itself, no. A lot of lichen on a tree whose canopy is thinning means the tree is under stress, and the stress is what needs attention.

Can I spray something to get rid of it?

Copper fungicides will kill lichen. It is a cosmetic treatment with no benefit to the tree, and it comes back if the tree does not regain vigor.

Lichen is on my fence and roof too. Is it spreading from the tree?

Lichen spreads by airborne fragments and spores, and it grows on almost any stable, damp, sunlit surface. It is not spreading from the tree to the fence; both are just good habitat.

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ArboristRX diagnoses declining trees across Edgewater, Port Orange, New Smyrna Beach, Oak Hill and Volusia County. If your tree is thinning and the lichen is filling in, call (386) 444-5959 and we will look at the tree, not the lichen.