Green Growth on Maple Trunks: Algae, Moss, or Lichens—What It Means and What to Do

What It Likely Is

The green coating on your Norway maple trunks is most likely algae, moss, or lichens—not a harmful fungus. These organisms thrive on shaded, moist bark and do not parasitize the tree.

When to Clean

If the growth is unsightly, you can scrub the trunk with a dilute bleach solution: 1 part household bleach to 9 parts water (10% solution). Rinse thoroughly afterward.

No Treatment Needed

These organisms are harmless and often indicate good air quality. No control is necessary for tree health.