Mulch is one of the best things you can do for a tree. A proper ring of mulch holds moisture in our hot North Texas summers, moderates soil temperature, suppresses weeds, and slowly feeds the soil as it breaks down. Yet mulch applied the wrong way does real harm, and it is one of the most common mistakes we see in Arlington yards. The problem is almost never the mulch itself - it is how much and where it goes.
Volcano Mulching: The Most Common Mistake
Drive through almost any neighborhood and you will see it: mulch heaped up in a tall cone around the base of a tree, like a little volcano with the trunk poking out the top. It looks tidy, but it is quietly damaging the tree.
The trunk of a tree is not built to be buried. Its bark is designed to be exposed to air, not held against constant moisture. When mulch is piled against the trunk, it traps water and creates a dark, damp environment that invites decay, disease, insects, and rodents chewing on the bark. Over time this can rot the base of the tree and kill the very tissue that moves water and nutrients up and down the trunk.
Mulch Against the Trunk Invites Rot
Closely related is the habit of pushing mulch right up to the bark, even in a thinner layer. The root flare - the point where the trunk widens and meets the roots - needs to stay visible and exposed to air. Burying it under mulch keeps it perpetually damp and can lead to hidden decay and girdling roots that circle and slowly strangle the tree. If you cannot see where the trunk flares out into the ground, the mulch is too close and too high.
Piling It Too Deep
More is not better. When mulch is laid on too thick, it can actually work against the tree. A heavy layer can shed light rain before it reaches the soil, keep the ground waterlogged after heavy rain, and in some cases starve the roots of oxygen. Excessively deep mulch can also encourage roots to grow up into the mulch layer itself rather than down into the soil, leaving the tree less stable and more drought-sensitive.
How to Mulch the Right Way
Good mulching is simple once you know the target. Think donut, not volcano.
Get the Depth Right
Aim for a mulch layer roughly two to four inches deep. That is enough to hold moisture and suppress weeds without smothering the roots. If old mulch is still in place, rake it out and refresh it rather than piling new mulch on top year after year.
Keep It Off the Trunk
Pull the mulch back a few inches from the trunk so there is a clear gap of bare soil around the base. This is the donut shape: a ring of mulch with an open center. Keeping the root flare exposed lets the bark breathe and keeps decay and pests away from the trunk.
Spread It Wide
This is where most people stop too soon. Instead of a narrow ring, spread mulch out in a broad circle - ideally toward the drip line, the area under the outer edge of the canopy. That is where the feeder roots are working hardest, and a wide mulch ring benefits far more of the root system than a small collar around the trunk. A wider ring also keeps mowers and string trimmers away from the bark, preventing the wounds that let in decay.
A Quick Checklist
- Depth: two to four inches, no more.
- Shape: a donut with a gap around the trunk, never a cone.
- Trunk contact: none - keep the root flare visible.
- Width: spread out toward the drip line, not just at the base.
- Material: a natural wood or bark mulch that breaks down over time.
Getting mulching right is one of the easiest ways to keep your trees healthy for the long haul. If you are not sure whether past mulching has harmed a tree, or you would like your trees checked over, Treetop Tree Service offers free estimates. Call our ISA Certified arborists at 817-992-6670 and we will take a look.