Trees and Mulch

This is the #1 mulching mistake by far. It looks neat at first—but piling mulch in a cone or “volcano” shape against the trunk is all of the worst parts of these mistakes, trapping moisture and creating the perfect conditions for rot, pests, and fungal diseases. Over time, the bark breaks down, and the tree’s structural integrity can be compromised.
Its common for this to become an unintended problem due to our next mistake.

More mulch doesn’t mean more protection. A layer more than 2–4 inches deep prevents oxygen from reaching the roots and can lead to soil compaction, root suffocation, and poor drainage. Trees essentially begin to "drown" in overly thick mulch beds. 

Installing raised mulch rings, stone borders, or decorative retaining walls around the base of an existing tree might look attractive, but it’s one of the most damaging long-term practices. These artificial structures alter the natural soil grade and effectively bury the root flare and lower trunk. While no tree benefits from being planted long-term in a raised bed, installing them around a mature tree makes them particularly vulnerable because they didn’t grow under those conditions. This sudden change can suffocate roots, increase disease risk, and lead to a surprisingly quick decline.

Even if the mulch isn’t tall, applying it directly up against the trunk restricts airflow and traps moisture where it shouldn't be. This often leads to girdling roots and trunk decay over time, especially in young trees.

While organic mulch is generally preferred, not all materials are created equal. Mulch that hasn’t aged or composted properly can introduce weed seeds, harmful fungi, or tie up nitrogen in the soil. Shredded bark, dyed mulches, or overly acidic mixes can do more harm than good if not selected carefully. Non-organic mulches such as rock or rubber are often chosen for their low-maintenance appeal, but they are almost always poor choices for tree health in the Northern Virginia. These materials retain heat, disrupt soil biology, and prevent natural decomposition processes that benefit roots. In many cases, installing these types of mulch can actually increase long-term maintenance costs, especially if the tree suffers decline and needs to be replaced.

Weed barrier fabric is often installed with good intentions, but it causes more problems than it solves—especially around trees. Over time, the fabric blocks air and water from reaching the soil, prevents natural nutrient cycling, and creates a layer where roots begin to grow sideways or upward in search of oxygen. This can lead to root girdling and long-term decline. Worse still, it doesn't actually stop weeds in the long run—most weeds just root into the mulch layer above the fabric.
Many alternative options exist to manual weeding such as the application of organic corn gluten meal, granular chemical preemergent, or even spot treating or torching. 

Over time, especially with finely shredded mulch, a hard surface layer—or "crust"—can develop. This mulch crust prevents water and air from penetrating into the soil where roots need them most. If left unbroken, it can lead to dry, compacted soil and force tree roots to grow near the surface in search of oxygen and moisture. Breaking up this crust before adding additional mulch (the preferred method) allows the decomposition process to complete itself, releasing nitrates and other nutrition in to the soil for the tree to use.  

This may seem like a no-brainer, but leaving the soil bare exposes a tree’s root structure to temperature extremes, erosion, moisture loss, and physical damage. Without mulch, there’s also no barrier to protect the tree from lawn equipment, foot traffic, or vehicle compaction. Even a small, properly applied mulch ring can offer essential protection and is far better than no mulch at all—both for aesthetic reasons and for promoting long-term tree health.

Girdling roots exposed and removed after removing the mound at the base of an over mulched tree. Professional interventions like these can make a huge difference in the health of your tree,

All of the photos above are results of root zone issues. In the worst case, the failures are complete and catastrophic.