03/15/2026
Volcano mulching is the most visible tree care mistake in America and the hardest to stop — because every landscaping crew does it, every neighbor copies it, and the mulch companies sell it by the cubic yard to pile up higher.
The cone of mulch banked against a tree trunk is not protecting anything. It is trapping moisture against bark that evolved to stay dry. Tree bark is the tree's skin — it breathes, it sheds water, and it serves as the first defense against pathogens and boring insects. Burying it under six to twelve inches of wet decomposing mulch rots the bark, invites fungal infection into the cambium layer, and creates an entry point for decay that can hollow the trunk from the inside.
The damage happens underground too. Mulch piled against the trunk encourages circling roots that grow around the base instead of spreading outward. Over years, these girdling roots tighten like a belt around the trunk, slowly strangling the tree's own vascular system. By the time symptoms appear above ground — thinning canopy, early leaf drop, bark cracking — the girdling is often too advanced to correct.
The correct mulch application looks underwhelming by comparison. A flat ring of mulch two to four inches deep extending out to the drip line — with a six-inch gap of bare soil around the trunk exposing the root flare — is what every university extension and certified arborist recommends. The root flare is the widening at the base where trunk becomes root. If you cannot see the flare, the tree is buried too deep or mulched too high.
The irony is that mulch itself is excellent for trees. It retains soil moisture, moderates root zone temperature, suppresses weeds, and adds organic matter as it decomposes. The material is not the problem. The placement is. Three inches of mulch in a wide ring with a clear trunk gap does everything a volcano promises and nothing it threatens.
If your trees currently have mulch volcanoes, pull the mulch back to expose the trunk and root flare. Redistribute it in a flat ring. The bark underneath may already show discoloration, softness, or fungal growth — clearing the mulch now stops the process before it reaches the cambium.
The tree that looks least cared for at the curb is often the healthiest one on the block
