Above image from Purdue Extension publication FNR-585-W, Surface Root Syndrome
I’ve had some recent interactions with people frustrated by tree roots that surface, causing mowing difficulties and potential ankle-twisting opportunities. What can be done with surface roots?
Lindsey Purcell, former Purdue Extension urban forestry specialist, authored an Extension publication on this phenomenon.
“Genetics determine the characteristics of root growth in a tree, but generally speaking, tree roots develop similarly among temperate zone species,” said Purcell. He added that a tree’s lateral roots, those growing horizontally from the upper part of the taproot, are often the most vigorous and form the main framework and support to anchor a tree.
“Examples of trees with shallow root growth include maples, sycamores, willows and some ash species,” he said.
“These shallower roots rise to the upper, nutrient-rich layers at the surface of the soil,” said Purcell. “Then, as traffic occurs – such as mowers and foot traffic – the soil is eroded away, exposing the roots and creating a maintenance challenge.”
Purcell poses the question that is at the crux of the matter, “How can surface root issues be improved without compromising tree health?”
Many attempts to solve this problem have been attempted by homeowners. Purcell stated that common strategies attempted by homeowners, but not recommended, include removing visible surface roots by cutting or grinding, adding a heavy layer of topsoil to cover exposed roots, and planting a raised flower garden or groundcover over surface roots.
“The best solution for bothersome surface roots is simply to mulch,” said Purcell. “Wood mulch is the best way to cover tree roots above the ground.” He suggested 2-3 inches of wood mulch to reduce the need to mow over the roots and increase moisture retention in the root zone. “For best results, create a mulch ring that extends out to the dripline, if possible, or at least to where the surface roots have dissipated enough for healthy turf growth,” he said. The dripline is the invisible vertical line where the tips of lateral branches end.
Alternatively, you may wish to plant shade tolerant species among the roots, perhaps in your newly mulched area as recommended above, and eliminate grass altogether. Don’t add extra soil, as this would violate one of the aforementioned ‘what not to do’ items. It’s also best to avoid planting anything next to the trunk. Some species to consider would include hosta, cardinal flower, Solomon’s seal, and similar plants, or a native groundcover species. This type of planting would solve the issue of difficult mowing and would provide a new visual aesthetic to your landscape.
“When dealing with surface root syndrome, be certain that any mitigation does not compromise tree health and increase the risk for tree failure,” said Purcell. While troublesome, he said that homeowners can make a positive change in the landscape and create an environment where trees and turf can survive harmoniously together.
Find Purcell’s publication FNR-585-W entitled, “Surface Root Syndrome,” at www.edustore.purdue.edu. Find suggestions on plants for shady areas by Rosie Lerner, former Purdue consumer horticulture specialist, at https://www.purdue.edu/hla/sites/yardandgarden/perennials-for-shady-gardens/.