Oak Burls: Harmless Oddities Prized by Woodworkers

What Those Bulging Growths Are

The 12-inch round swellings on your oak trunk—and the new ones appearing nearby—are burls: abnormal, tumor-like growths of woody tissue. Their exact cause is often unknown; some are linked to the Phomopsis fungus, but most are not considered pathogenic.

No Harm, No Removal

• Burls do not threaten tree health.
• Cutting them out creates a large wound that invites decay and disease.
• Woodturners and artisans value burl wood for its spectacular grain patterns.

Enjoy them as natural sculptures; they’re a sign of a living, reacting tree.