Why "Volcano Mulching" is Killing Twin Cities Trees (And How to Fix It)

As a homeowner in the Greater Twin Cities Metro Area, you already know that keeping your landscaping alive through our brutal, unpredictable seasons is a full-time job. Between the freezing winters, the heavy snow loads, and the inevitable summer droughts, our trees take a beating.

So, when spring finally arrives in St. Paul, it’s natural to want to give your trees a boost by laying down a fresh, thick layer of mulch. Unfortunately, a massive, well-intentioned trend is silently suffocating our local canopy. Take a drive down any street in the metro, and you'll see them everywhere: "Mulch Volcanoes."

Piling mulch high up against the trunk of a tree might look neat and tidy, but in the Minnesota climate, it is a localized death sentence for your landscaping. Here is why volcano mulching is so dangerous, and how to properly mulch to ensure your trees thrive year-round.

The Dangers of the Mulch Volcano

Mulch is supposed to mimic the forest floor—insulating roots, retaining moisture, and breaking down into essential nutrients. But when you stack it 10 inches high against the trunk of a tree, you are fundamentally altering how the tree survives.

1. Suffocating the Root Flare

A tree breathes through its root flare—the wide, bell-shaped base where the trunk meets the roots. When you bury this flare in a volcano of mulch, you literally suffocate the tree, starving it of the oxygen it needs to survive our humid Minnesota summers.

2. Trapping Moisture and Rot

Tree bark is designed to protect the tree, but it is meant to be exposed to the air. A mulch volcano holds constant, damp moisture directly against the bark. In St. Paul, where our soil is already often dense clay, this trapped moisture quickly leads to fungal infections, cankers, and inner wood rot.

3. The Freeze-Thaw and Rodent Threat

Here is where the Minnesota climate makes things worse. As we hit the deep freeze of winter, a mulch volcano provides a warm, insulated, and hidden nesting ground for mice and voles. Beneath the snow line, these rodents will happily chew right through the rotting bark, girdling the tree and killing it before the spring melt even begins.

4. Girdling Roots

Desperate for oxygen and water, a buried tree will start growing secondary roots up into the mulch volcano rather than down into the soil. As these roots grow in circles around the trunk, they eventually strangle—or "girdle"—the main trunk, cutting off the flow of nutrients completely.

The Solution: The "Mulch Doughnut"

Instead of a volcano, your trees need a doughnut. Proper mulching protects the soil without compromising the tree's health.

• The Right Depth: Spread a high-quality hardwood or cedar mulch no more than 2 to 3 inches deep over the root zone.

• The Right Distance: Keep all mulch at least 3 to 6 inches completely away from the base of the trunk. The root flare must be visible and exposed to the air.

• The Right Width: Extend the mulch ring out as far as you can—ideally to the "drip line" (the edge of the tree's canopy) to protect the shallow feeder roots from mower damage and temperature swings.

The DIY vs. Pro Reality Check

Digging out existing mulch volcanoes, carefully exposing the delicate root flare without damaging the bark, and hauling in yards of fresh, properly applied mulch is incredibly tedious, heavy work. You are a Minnesotan—you certainly have the grit to spend your weekend shoveling and raking.

But frankly, you shouldn't have to.

Correcting years of bad mulching often requires a delicate touch to avoid slicing into girdled roots or infected bark. A mistake with a shovel can do just as much damage as the mulch itself. Plus, dealing with the heavy, compacted clay soil of St. Paul while trying to promote healthy root growth is a headache you don't need on your day off.

Let the experts take this off your plate. We know exactly what our local trees need to survive the extreme swings of the Twin Cities climate.

Protect Your Property with Monson Lawn and Landscaping

At Monson Lawn and Landscaping, we specialize in comprehensive property care tailored strictly to the realities of St. Paul and the surrounding metro. From custom fertilizer and weed control for your cool-season grasses to flawless landscaping installations and 24/7 snow removal, we are your local authority.

Don't let improper mulching destroy the most valuable assets in your yard. Contact Monson Lawn and Landscaping today for a free quote, and let us handle the heavy lifting so you can simply enjoy a beautiful, healthy property year-round.