Deep Roots of Landscape Trees

When structural root systems of landscape trees are too deep, reduced vigor, decline, and even death can result. Although deep roots have existed for decades, awareness of them has been increasing recently. Many think the problem is actually getting worse.

The structural roots are the large woody roots giving characteristic form and shape to the root system. They should originate near the base of the trunk, just below the soil surface. The connection of the structural roots to the trunk, results in development of a pronounced root flare (a.k.a. trunk flare) as the tree ages. In many species, the structural roots remain within a few inches of the soil surface as they spread out. (In the photo, several inches of soil have been removed to show the shallow structural roots.) In other species, they may grow down at a steeper angle.

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Absence of a root flare is a clear signal that the roots may be too deep. Nursery production and planting in the landscape can both contribute to deep roots, though in the end, the cause matters little because the results are the same.

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Though the problem starts below ground, the effects will eventually be seen above-ground. In extreme cases, crown decline can begin to show within a year after planting. The symptoms can also be more gradual.

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To address this industry-wide concern, in 2003, the American Nursery and Landscape Association and the International Society of Arboriculture proposed forming a National Working Group with broad green industry representation. The project is coordinated through the Morton Arboretum. Work is ongoing and this website will be updated periodically to include new information.

The USDA Forest Service Urban and Community Forestry Program, on the recommendation of the National Urban and Community Forestry Advisory Council, has provided grant support for research and technology transfer, including development of this web page that includes:

the latest research results,
Best management practices, and
Proceedings of the ‘Getting the Roots Right’ Conference. [3,376kb pdf]