With the planting season just a couple months away many of us will be mulching, including our trees. When mulching a tree, make sure the mulch is NOT touching the tree. Keep the mulch about 3 inches away from the tree. Mulch against a tree will prevent the tree trunk from drying and over time the tree will begin to rot, thus killing it (similar to wood that rots because it is always wet). Many times, mulch is layered around the tree in a “volcano” fashion, named that way because the mulch rises up like the shape of a volcano. It might look good, but it’s bad for the tree. If you have already put mulch against your tree, no biggie. Simply pull it away from the tree and give it time to dry.
Lastly, avoid layering mulch more than 2-3 inches high. Mulch that is piled too high can prevent rain water from adequately penetrating the ground.
Here are a couple sources that warn against leaving mulch against a tree: