Why You Should Never Mulch Against Tree Trunks
Mulch volcanoes are the most common landscaping mistake in the Northeast — and one of the most damaging. Here's what they do, why they're so common, and how to fix them.
Drive any suburban street in northern New Jersey and you'll see them — mulch piled into 12-inch cones around tree trunks like little brown volcanoes. It looks neat. It's expensive. And it slowly kills the tree.
This is the single most common landscaping mistake in the Northeast, and almost every homeowner is doing it.
What's actually happening
Tree trunks are not roots. Their bark is designed to be exposed to air. When mulch is packed up against the trunk:
- Moisture is trapped against the bark, encouraging rot
- The bark stays soft and is easy for insects and disease to enter
- Roots begin growing upward into the mulch instead of outward into soil — creating girdling roots that can strangle the tree
- The crown flare (where the trunk widens at the base) gets buried, which interferes with the tree's natural systems
Why it's so common
Mulch volcanoes spread because they look intentional. Many crews build them because they assume the customer wants them — or because it lets a small amount of mulch look like more.
It became a pattern, and the pattern outlived its original purpose. Most homeowners now think a mulch cone is the right look because they see it everywhere.
How to mulch around a tree the right way
- Pull mulch back 3 to 4 inches from the trunk in every direction
- The root flare — the place where the trunk widens at the base — must be visible
- Mulch should be flat, not coned — like a doughnut, not a volcano
- Total depth across the ring: 2 to 3 inches, same as the rest of the bed
- Extend the ring outward 2 to 3 feet around the tree, especially for younger trees
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Request a Free QuoteIf your trees already have volcanoes
Don't panic, but do fix it. Pull the mulch back from every trunk this spring. Check for girdling roots growing in the loose material — if there are major ones, a certified arborist can advise on how to handle them.
Once the trunks are clear and the rings are flat, you'll be surprised how fast the trees respond. Within a year or two, growth and color improve visibly.
What to ask your landscaper
Before any mulch install: "Are you going to keep mulch off the trunks?" If the answer is anything other than a confident "yes, of course," that's the wrong crew for your trees.
Flat, not coned. Pulled back from the trunk. Two to three inches deep. Your trees will thank you for it for the next thirty years.
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