An oak tree in my yard has a large growth on it. It doesn’t seem to be hurting the tree, but should I be concerned? BI

It’s sounds like you are describing what is known as a burl. Burls are round or irregularly shaped bumps or bulges found on trees. Their cause is up for discussion but essentially, burls are the result of abnormal growth caused by either a bacterial infection, a virus, fungi, or insects. How’s that for narrowing it down.

If their cause was better understood, it’s likely that someone would be producing them commercially because burls are prized by woodworkers for their unique grain patterns. Burls do not seem to damage the tree but one thing that will damage the tree is removing the burl from a healthy tree.

Removing a burl will result in an open wound on the tree that will leave it vulnerable to decay and disease. So, if you have a burl, just enjoy it for its uniqueness. If the tree ever needs to come down, maybe contact your favorite woodworker so they can make something special for you. Burls are often fashioned into bowls or veneers and can be used to make unique musical instruments like guitars.

Burls are just one of several naturally occurring curiosities concerning trees that do not cause damage to the tree. Another one that is pretty common is lichen. Lichen is an unusual organism because it exists as a combination of two unrelated organisms: an algae and a fungus. In lichens, these two coexist and behave as a single organism; one benefiting the other.

The algae photosynthesizes to provide energy while the fungus gathers water and minerals. Together they make up what is called a lichen thallus. The color and growth patterns of these cohabitants are used to classify them into different varieties of lichens.

The most common lichens tend to be grey green in color, but others can be found that are orange, yellow, dark blue, or black. While they live on the surface of the tree, they do not cause disease problems or penetrate the tree.

Shade tends to limit the growth of lichens, but they can grow rapidly on dead or dying trees as well as severed branches due to increased sunlight. Interestingly, lichens are not just found on trees, but can also grow on rocks, soil, or any other sunny surface.

Oftentimes when picking up dead and decayed branches that have dropped out of a tree, you will find part of the dead branch covered in lichens. You also may have seen lichen growing on an older tombstone and not know what it was. Now you do.

Either way, burls and lichens are interesting anomalies in the natural environment that won’t harm your trees. Good luck.

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org.

Burl photo  Joseph OBrien, USDA Forest Service, Bugwood.org