Mulch volcano vs mulch donut — how to mulch around a tree without rotting the trunk
Same volume, two shapes. The volcano piles mulch against the bark — trapped moisture rots the trunk, buries the root flare, and drives girdling roots. The donut lays an even 2–4″ layer pulled 3–6″ back from the trunk, keeping the root flare dry and tapering out to the drip line (ISA guidance).
What this diagram shows
A wrong-versus-right comparison of mulching a tree with the same volume of mulch in two shapes. On the left, the mulch volcano piles mulch high against the trunk: it traps moisture on the bark, causing rot, pests, and girdling roots, and it buries the root flare. On the right, the mulch donut lays an even 2-to-4-inch layer pulled 3 to 6 inches back from the trunk, leaving a mulch-free collar so the root flare stays exposed and dry, and tapering the layer out toward the drip line. Keep mulch 3 to 6 inches off trunks and stems per arborist (ISA) guidance.
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