Adventitious Roots

Adventitious roots are roots that develop from plant organs other than the primary root system. In trees, they most commonly arise from the buried portion of the trunk when the root collar is covered by excessive soil or mulch. While some species like willows and many tropical trees naturally produce adventitious roots, their appearance on species that do not normally form them is often a sign of problematic conditions.

When a tree's trunk is buried too deeply, either from improper planting, mulch accumulation, or soil grade changes, the buried bark tissue may respond by producing adventitious roots. While this might seem like a positive adaptation, these roots often grow in a circling pattern around the trunk rather than radiating outward. Over time, these circling roots can become girdling roots that constrict the trunk, impeding the flow of water and nutrients and eventually strangling the tree.

The presence of adventitious roots above the original root collar is an important diagnostic indicator during tree assessment. It tells the arborist that the root collar has been buried and that girdling root problems are likely. Root collar excavation to expose the original flare and remove circling adventitious roots is a common remedial treatment. Prevention through proper planting depth, where the root flare is at or slightly above grade, is far simpler than correction after the fact.