Tree roots growing at or slightly above the soil surface are called surface roots. For many home owners these roots are a nuisance as they dull mower blades, trip running feet, buckle sidewalks and crack driveways on occasion.
Cause/Conditions
A full understanding of tree root systems, soil, and tree biology is necessary when evaluating why a particular tree at a specific site has surface roots. It is often said that certain species trees are prone to surface roots. These trees are usually bottomland/wetland species that can only find the required level of oxygen near or on the surface. Roots, by nature, are merely seeking out and trying to obtain available resources from the soil. Roots grow where soil resources are most plentiful.
Roots growing on the soil surface may be trying to escape bad soil conditions below. These conditions can include compaction, presence of toxins, low oxygen, excess water, lack of water and competition from other plant roots. Erosion of soil also plays a part in exposing many surface roots. Root buoyance can be a cause of surface roots. Tree roots can buoy to the surface because the density of the materials that make up a tree root is lighter than the mineral components of soil. Over many years, with surface vibrations, frost heaving and compaction, the soil may “buoy” roots to the surface.
Control
Once roots appear on the surface, there are two options that can remedy the situation without substantially damaging the tree.
Mulching the area is the best solution. A 2-3 inch layer of wood mulch can be used to eliminate the need for maintaining grass near the surface roots. Existing grass can be killed with a product like Roundup that contains the active ingredient glyphosate. (Please read and follow label directions carefully, so as not to kill your tree) Existing grass can also be killed by laying 3-5 sheets of newspaper down and applying the mulch on top of the paper. Wetting the paper with water will hold the paper in place while allowing time for the mulch to be applied. Mulching creates a better growing environment for the tree and keeps lawn mowers and string trimmers away from surface roots and the trunk of the tree.
Planting perennial ground cover is another attractive way to deal with surface roots. The plants must be shade tolerant and able to compete with vigorous tree roots. These include Bugleweed, Lady’s Mantle, European Ginger, Chinese Astilbe, Bergenia, Lily-of-the-Valley, Epimedium, Sweet Woodruff, Perennial Geranium, Daylily, Hosta, Dead Nettle, Forget-me-not, Pachysandra, Lungwort and Periwinkle. Do not mound soil up over the roots to create a raised bed planter. Prepare the planting site as for mulching. Minimize root damage by plug planting – dig small holes, only as large as needed for planting. Mulch around new planting.
Unfortunately the first and last treatment many people use for a surface root solution is cutting. Roots are growing there for a reason. Cutting them out simply makes the tree’s plight worse and can lead to long-term decline, tree death or a hazardous tree situation.
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