Lichens like plants that are under stress

This is a lichen growing on a dogwood twig.  Lichens do not harm the plant, but they are an indication of poor plant growth.

This week, I was asked by a home gardener about an azalea problem. She described the problem as a greenish-white, crusty, scaly growth completely covering the branches on several of her azaleas.

It turns out she was describing a lichen. Gardeners often see these growths on bushes and trees and think it is a disease. However, lichens do not harm plants.

Lichens are interesting. They are actually two separate organisms, a fungus and algae. They form a partnership. Biologists give this partnership a fancy name. They call it a mutualistic symbiotic relationship.

Like all mutually beneficial partnerships, each party provides something and each party gets something. Algae capture the sun’s energy through photosynthesis. Algae share some of its energy with its fungal partner. The fungal partner protects the algae and provides water. In most cases, the fungus actually surrounds the algae cells. This robust partnership allows lichens to thrive in extreme environments, including the arctic. In fact, lichens are an important part of reindeer diets.

Lichens grow on limbs, branches, stumps, rocks, fence posts and soil. Lichens only need three things to be able to grow. They need a place to attach, sunlight and clean air. Pollution will reduce lichen growth.

Lichens on trees and bushes are typically a sign of poor health. When plants grow too slowly, the foliage thins. This allows more light for lichens to thrive.

Plants decline because of environmental stress, poor management or bad site selection. When plants are stressed, they are more likely to have heavy lichen growth. Keeping plants healthy is the best way to reduce the lichens. For plants with lichens, prune out the dead wood and lightly prune the affected plants. Apply fertilizer, too. Pruning and fertilizer both stimulate new growth.

Lichens are important partners in nature’s ecosystem. They are early colonizers that establish life on rock and barren sites. Lichens play an important role in soil formation over much of the earth. As lichens colonize rocks, they trap dust, silt and water. When they die, they contribute decayed organic matter to the area they inhabit, which allows vascular plants to begin developing among the pockets of new soil.

For more information on lichens, visit Millie Davenport, Clemson Horticulture Extension Agent’s online video at In this video she discusses additional information on lichens.

Seth Nagy is the County Extension Director in Caldwell County.


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