Our office has been getting samples and calls about a light green flaky material growing on shrubs and trees. The light green flaky material is — lichens.

Lichens are harmless, but it often indicates that something is wrong with a plant or tree. Lichens do not grow on young, healthy, and active growing trees. On the other hand, stressed trees or shrubs grow very slowly and often have lichens growing on them.

Lichens are not pathogens, meaning they don’t cause disease in plants. They use the plants as a surface to grow on. When a tree or shrub begins to decline due to some sort of environmental stress or other disorder, the leaf canopy thins and allows sunlight to enter and begin lichen growth. If overall plant health is improved, a dense leaf canopy should inhibit any sunlight available for lichen growth.

Lichens can be found on trees planted in small islands or beds near parking lots. These trees are stressed by limited soil and root growth, compacted soils and heat stress due to paved surfaces.

If you see lichens growing on trees or shrubs in your landscape, this is a clue that something could be causing your plants to grow slowly and decline in health. This could be a combination of factors like plant competition, drought stress, over watering, soil compaction, poor nutrition, improper pH, or improper pruning. Most common causes of lichens are drought or improper plant nutrition.

If you remove what is stressing your trees or shrubs, the lichens will go away. For further information about plant fertilization or irrigation, contact our office at 770-749-2142 or email