If you drive through almost any neighborhood in Rapid City or the surrounding Black Hills communities, you will see them. They are tall, cone-shaped piles of mulch piled high against the trunks of trees, often resembling a small volcano. Landscapers and homeowners create these “mulch volcanoes” because they believe they look neat and help the tree retain moisture. In reality, piling mulch against the trunk of a tree is one of the fastest ways to slowly kill it.
Trees are not designed to have their trunks buried. When organic material like mulch traps moisture against the bark, it creates the perfect environment for rot, fungal diseases, and suffocating root growth. Understanding how to properly mulch a tree, and how to fix a tree that has already been buried, is critical for protecting your landscape investment. This guide will explain the dangers of mulch volcanoes, the proper way to apply mulch, and how a process called root collar excavation can save a tree that is suffocating.
Why Mulch Volcanoes Are So Dangerous to Trees
To understand why mulch volcanoes are harmful, you have to understand how a tree is built. The point where the trunk widens and transitions into the root system is called the root collar or root flare. This specific area of the tree is designed to be exposed to the air. The bark on the trunk is completely different from the bark on the roots. Trunk bark is meant to protect the tree from the elements, while root bark is designed to handle constant moisture and soil contact.
When you pile mulch high against the trunk, you are forcing trunk bark to act like root bark. The mulch traps water against the wood, keeping it constantly damp. Over time, this moisture causes the bark to rot and break down. Once the bark rots away, the inner wood of the tree is exposed to fungal infections, bacteria, and wood-boring insects. This decay process can take years, meaning the tree might look fine on the outside while slowly rotting away at the base. By the time the canopy starts showing signs of distress, the structural integrity of the tree is often completely compromised.
The Threat of Stem Girdling Roots
Rot and disease are not the only problems caused by improper mulching. Trees are incredibly adaptable organisms, and their roots will grow wherever they find moisture and oxygen. When a thick layer of mulch is piled around the trunk, the tree will often send new roots up into the mulch pile rather than down into the soil. Because these roots are growing in a confined space around the trunk, they tend to circle the base of the tree rather than spreading outward.
These circling roots are known as stem girdling roots. As the tree grows and the trunk expands in diameter, these circling roots also grow thicker and stronger. Eventually, the roots act like a tight collar, slowly strangling the trunk and cutting off the flow of water and nutrients between the canopy and the root system. Girdling roots are a leading cause of premature tree death in urban and suburban landscapes, and they are almost always the direct result of planting a tree too deeply or burying it under a mulch volcano.
How to Properly Mulch a Tree in the Black Hills
Mulch is highly beneficial for trees when applied correctly. It regulates soil temperature, retains moisture during the hot South Dakota summers, and keeps lawnmowers and weed trimmers away from the trunk. The key is to apply it in a way that mimics the natural forest floor. The ideal mulch application is often described as a “doughnut,” not a volcano.
To properly mulch a tree, start by pulling all existing mulch and soil away from the base until the root flare is completely exposed. You should clearly see where the trunk widens out into the main structural roots. Next, apply a layer of organic mulch that is no more than two to three inches deep, spreading it out as far as the tree’s drip line if possible. Most importantly, leave a gap of at least three to four inches between the inner edge of the mulch ring and the trunk of the tree. The trunk and the root flare must remain completely bare and exposed to the air.
Saving a Buried Tree with Root Collar Excavation
If you have a tree on your property that has been buried under a mulch volcano for years, simply pulling the mulch away with a rake might not be enough. The soil underneath may have compacted, and girdling roots may have already started to form. In these cases, the tree needs a specialized arborist service known as root collar excavation. This process safely removes the compacted material and exposes the root system without damaging the tree.
During a root collar excavation, an arborist uses a specialized tool called an AirSpade. This tool uses highly compressed air to blow away the dirt and mulch, leaving the roots completely intact. Once the root flare is exposed, the arborist can inspect the area for rot and carefully prune away any stem girdling roots before they can strangle the tree. This process instantly relieves the stress on the tree, allowing it to breathe, absorb nutrients properly, and recover its health.
Give Your Trees Room to Breathe
Do not let a simple landscaping mistake destroy the mature trees on your property. Canyon Falls Tree Works provides expert root collar excavation and plant health care services across Rapid City and the Black Hills region. Our ISA Certified Arborists will safely expose your tree’s root flare, remove dangerous girdling roots, and ensure your trees have the foundation they need to thrive. Call us today at (605) 898-8733 or visit our website to request your free estimate.
Frequently Asked Questions
How do I know if my tree has a mulch volcano?
Look at the base of the trunk where it meets the ground. If the trunk goes straight into the soil or mulch like a telephone pole, it is buried too deeply. Canyon Falls Tree Works advises that you should always be able to see the root flare, which is the natural widening at the base of the tree.
Can a tree recover from girdling roots?
Yes, if the problem is caught early enough. Canyon Falls Tree Works uses specialized tools to expose the root collar and carefully cut away the circling roots before they completely strangle the trunk. Once the pressure is relieved, the tree can often make a full recovery.
What is an AirSpade and how does it work?
An AirSpade is a professional arborist tool that uses a high-velocity stream of compressed air to move soil. Canyon Falls Tree Works uses this technology because it safely blows dirt away from the root system without cutting or damaging the delicate roots underneath.
Is it too late to fix a tree that has been buried for years?
It is rarely too late to try, but the success rate depends on how much rot has already occurred at the base. Canyon Falls Tree Works can perform an inspection to determine if the structural wood is still sound before proceeding with a root collar excavation.
What kind of mulch is best for trees in Rapid City?
Organic, undyed wood chips or shredded bark are the best options. Canyon Falls Tree Works recommends avoiding rubber mulch or dyed mulches, as they do not break down to provide nutrients to the soil and can sometimes leach unwanted chemicals.