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How to mulch around a tree 
Shovel away old mulch, dirt, and rocks. 
Shovel away all the old mulch, debris, and rocks so that you can see the tree trunk. A " mulch volcano " occurs when mulch is piled up year after year on the base of a tree.
Mulch piled up at the base of a tree is detrimental and starves the roots of needed oxygen. Cut up-growing roots with pruners.