Craig Hignight explains what those lumps are on your tree leaves WQAD Digital Team Replay Video UP NEXT Got galls? Don't worry. Experts say they're typically not harmful to your plants. Galls are abnormal growths that develop on either budding or mature plants. During Good Morning Quad Cities at 11 on Wednesday, June 9, plant and garden expert Craig Hignight said galls frequently seen on trees like maples or oaks. "The tree doesn't even know it's there," he said, showing some galls during his question and answer segment.