Lichens on Trees: Harmless Epiphytes or Hidden Threat?

Those gray-green, crusty, leafy, or bushy growths on your tree’s bark are lichens—a symbiotic union of fungi and algae (or cyanobacteria). They manufacture their own food via photosynthesis and use the tree merely as a substrate. Far from being parasites, they are epiphytes that derive nutrients from air and rain.

Three Growth Forms

• Crustose: Tightly appressed, crust-like patches.
• Foliose: Leaf-like, loosely attached lobes.
• Fruticose: Shrubby, erect or hanging strands.

Are They Harmful?

Research shows only a slight negative effect—possibly minor interference with gas exchange or moisture retention. The primary concern is aesthetic: lichens give trees an "unkempt" look. Crucially, they are indicators of a thin canopy, not the cause of decline. A dense, healthy canopy shades the bark, reducing photosynthesis and naturally suppressing lichen growth.

Management: Focus on Tree Health

• Do not use chemical controls (copper fungicides, baking soda sprays). They offer only temporary cosmetic improvement and are not labeled for lichen control.
• Improve tree vigor. Fertilize with 10-10-10 at 1 lb per inch of trunk diameter, scattered under the drip line and watered in.
• Promote canopy density. Proper watering, mulching, and pruning encourage foliage that shades out lichens.

Bottom line: Lichens are a symptom, not a disease. Invest your effort in overall tree health, and the lichens will diminish as the canopy fills in.