Greenish Growth on Cherry and Lilac: Lichens Signaling Tree Stress

Identification: It's Lichens

The green-silvery, flower-like or crusty growth on bark is lichens—a fungus-algae partnership. They photosynthesize (algae) and gather minerals (fungus). They are not pathogens.

Why They Indicate Stress

Lichens proliferate when canopy thins, allowing light onto bark. Common stressors:

• Drought
• Old age
• Poor pruning (dense, crossing branches)
• Nutrient depletion

Restoration Plan

1. Prune correctly: Remove crossing branches, deadwood. Open center for light/air penetration.
2. Scratch test: Nick bark—green/cream = alive. Brown = dead; remove to live tissue.
3. Soil test: Sample at drip line. County extension will prescribe N-P-K needs.
4. Fertilize per results: Often nitrogen and potassium are low in neglected landscapes.

Lichen Suppression (If Desired)

Bordeaux mixture (copper sulfate + lime) or copper sulfate alone kills lichens organically. Apply per label; 2–3 treatments spaced 2 weeks apart. But—addressing the underlying stress is the only lasting solution.

Healthy, well-pruned, fertilized trees naturally outgrow lichens.