Q: My neighbor has a five-trunked Japanese magnolia. The crotch in the middle is about 8 inches deep and there’s usually 5 to 8 inches of water in it. She wants to drill a hole in it from the side so the water could drain. Should she do anything?
A: Tree experts agree that drilling a drainage hole is a bad idea. The tree is able to “wall off “ the wet area itself, with no human help. Drilling a drain hole just gives rot fungi a good route into the trunk.
My advice is to leave it alone but keep an eye out for mosquitoes that might breed in the water. You can use a “mosquito doughnut” to keep them away.