Hidden Stress Below the Surface: Understanding Root Collar Disorders
- Austin Cowen
- Nov 4
- 2 min read
Root collar disorders—often caused by girdling roots or a buried root flare—are some of the most common structural and physiological problems affecting urban trees. Because the issues begin below the soil line, they can go unnoticed for years until decline is well underway. Early identification is key to preventing long-term canopy loss, structural failure, and tree death.
What Is the Root Collar?
The root collar is where the trunk transitions into structural roots. This zone must remain exposed at grade level for proper oxygen exchange and stable root development.When soil or mulch is piled against the trunk, the root flare becomes buried, prompting the tree to produce adventitious roots that often circle or compress the trunk—forming girdling roots.
How Girdling Roots Form
A variety of common landscape conditions contribute to girdling roots:
Improper Planting Depth- Low planting depth reduces available oxygen, forcing roots to grow upward and around the trunk in search of aerated soil.
Excessive Mulch- Over-mulching (“mulch volcanoes”) holds moisture against the trunk and stimulates root growth into the mulch layer, where roots can easily circle back toward the stem.
Nursery Circling Roots- Container-grown trees sometimes retain circling roots from their early production phase, and these patterns continue as the tree matures.
Restricted or Compacted Soil- Urban soils often prevent normal radial root expansion, forcing roots to follow the path of least resistance—frequently around the trunk.
How It Affects Tree Health
Girdling roots create slow, chronic decline. Typical impacts include:
Reduced vascular flow between canopy and roots
Thinning canopy, small leaves, and early fall color
Poor structural stability and increased risk of failure
Minimal or absent visible root flare
Maples, lindens, crabapples, and serviceberries are especially prone in Northwest Indiana.
How Arborists Diagnose the Problem
Diagnosis typically involves a root collar excavation, where an air spade is used to remove soil without damaging roots. Exposing the root flare allows the arborist to clearly see any circling or adventitious roots, areas of trunk compression, decay, or structural weakness. This simple but essential process reveals issues that aren't visible at the surface and guides the appropriate corrective treatment.
Treatment Options
Depending on severity, management may include:
Selective removal of girdling roots
Re-establishing proper soil grade around the root flare
Correcting mulch depth and placement
Supportive care (watering, fertilization, structural pruning)
Severe cases where the trunk is significantly constricted may require removal for safety.
Why Early Detection Matters
Root collar disorders often develop slowly and are easiest to correct in the early years after planting. Regular inspections can help prevent long-term decline, canopy loss, and structural instability.
If you suspect a root collar issue on your property, click the button below to schedule a professional assessment with NWI ArborCare today.
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