What is the wrong way to mulch a tree?
Mulch is a good thing for new trees, since it holds in moisture and insulates the soil. It’s especially good for new trees to give them a buffer zone to protect their young trunks if you’re mowing around them.
BUT, incorrect mulching can be detrimental to tree health. I bet you’ve seen mulch piled up against the trunk like a volcano. Don’t do it! Trunks of trees need light and air. Mulching against the trunk or climbing up it can kill your tree.
The right way to mulch: leave breathing room around the trunk of your tree. Away from the trunk, add about 3″ of mulch. It’s good to create a small berm of mulch at the edges to keep any rainfall or hose irrigation near the tree.
Try to expand the circle of mulch out to the drip line, which is where the farthest branches extend from the tree. The feeder roots, those that take up water and nutrients, will be located at and beyond this point, so this is the most critical area to protect.
Finer aggregate mulch tends to pile better, creating a better barrier against evaporation and soil erosion. Plus, finer aggregate mulch will break down better over time, adding organic matter to the surrounding soil. Since it does break down, mulch should be replenished or replaced; spring and fall are good times for that.
With the lack of rainfall and extreme summer heat in the last few years, young trees need all the help they can get during the first decade or so of their young lives.
With older, large trees, it’s still a good thing but not so essential. Once a tree is well established, it’s more efficient at taking up water. Also, maintaining mulch around such a large area is challenging, but as long as you’re watering slowly and deeply, mature trees will be just fine in those situations.