31/03/2026
https://www.facebook.com/share/1K8kYNZUWH/?mibextid=wwXIfr
I am not killing your tree. I am not a fungus, a moss, or a disease.
That gray-green crust on the bark of your oak. The leafy stuff on the branch. The dusty pale coating on the fence post. You've been searching for tree disease treatments for three years.
I'm a lichen. And your tree isn't sick. It's certified.
A lichen isn't a single organism. It's two organisms fused into one — a fungus and an alga living together as one body. The fungus provides structure, protection, and mineral absorption. The alga provides food through photosynthesis. Neither can live like this alone. Together they form something that resembles neither.
I grow on your tree. Not in it. My body attaches to the bark surface. I don't pe*****te the bark. I don't steal nutrients. I don't block light from the leaves. I don't cause decay. I'm using your tree as a surface the same way a bumper sticker uses your car.
Here's why I'm actually a good sign.
Lichen cannot grow in polluted air. Air pollution kills me. If your tree is covered in lichen, the air around your property is clean enough to support me. Ecologists use lichen presence to map air quality — more lichen species in an area means cleaner air. Your lichen-covered oak is a certificate of air quality you didn't know you had.
The tree you think is declining because of me is usually declining because of something else — drought stress, root compaction, pest damage — and I happened to be on the bark when you noticed. I was here before the decline started. I didn't cause it.
I grow a millimeter or two per year. The patch on your oak branch that's the size of your palm has been growing for decades. I was here before the deck was built. Before the house was painted. Before you moved in.
🌿 What to do about lichen on your trees:
- Nothing. Leave it. Lichen on bark is not a problem and removing it accomplishes nothing except damaging the bark surface underneath
- If a tree covered in lichen is declining, the cause is underground or internal — root damage, compaction, drought, boring insects. The lichen is a bystander, not the culprit. Investigate the roots and soil before blaming the surface
- Lichen on a fence post, stone wall, or garden structure is the same organism doing the same harmless thing. It adds texture and character and indicates clean air
- If lichen suddenly disappears from trees in your area where it used to thrive, that's a signal worth paying attention to — it may indicate a change in local air quality
- Lichen on fallen branches is a building material for hummingbirds and gnatcatchers. Both species press lichen flakes onto the outside of their nests with spider silk for camouflage. The lichen on your oak may end up on a nest in your yard
Don't scrape it off. Don't spray it. It's not the problem. It's the proof that the air is clean enough for it to exist 🌿
