Those Pesky Surface Roots
Over the past 27 years in arboriculture, the most asked question I received is regarding what can be done about surface roots. Unfortunately, there is no silver bullet and each situation might dictate a different answer. Before diving into this unending question, I want to point out the difference between surface roots and stem girdling roots. Stem girdling roots are roots that grow around the base of the tree compressing the cambium (first picture below). These will be discussed in other blog posts. Surface roots are roots that grow at or above the surface of the lawn (second picture below).
Stem girdling roots choking a Norway maple. If left alone, these roots will eventually cause the tree to decline or potentially fail in a storm.
Surface roots on a deeply planted linden tree disrupting the lawn and potentially causing concern for the patio.
Trees versus Lawns
Trees planted in a typical urban landscape grow in an unnatural environment. Urban sites often have compacted soil, restricted root space, and are covered in a thick blanket of turf. The majority of a tree’s rooting system grows in the top 1-2 feet of the soil and occupies some of the same area with turf roots. On the other side, trees will create an environment too shady for most lawn grasses. When lawn turf is thin, it is easier for weeds to invade. Also, surface roots can make it difficult for turf to be thick and healthy. There is direct competition between trees and lawn for nutrients and moisture.
When trees are planted in the urban environment, some issues can be expected, including surface roots. Surface roots can be unsightly, can cause damage to surrounding structure, can be a nuisance for mowing and can be a tripping hazard. When deciding how to handle the issue, please remember this is NOT a tree issue. This is a people issue. We plant trees in an environment that does not favor their natural growth patterns. A tree will grow however it will best survive and thrive.
What Causes Surface Roots?
Type of Tree-Many tree varieties are predisposed to having shallow-growing roots. Elm, willow, cottonwood, linden and several maple varieties (Norway, Silver, Autumn Blaze, Red) are all tree types that commonly have shallow growing roots, with many of them above the surface.
Soil Type and Condition-Many trees tend to grow shallow roots if the soil is compact, wet or a heavy clay. All of these conditions are unfavorable for soil oxygen, which is crucial for healthy roots. In conditions in which there is low soil oxygen (and compact soil), roots will grow above ground to gain access to oxygen and to avoid compact soil. The tree is essentially trying to survive a tough soil condition.
Growing Conditions-Many trees in urban settings grow in spaces that are insufficient to handle all of the roots of a shade trees. A single shade tree commonly needs a minimum of 2,000 square feet of root space for healthy growth.
Root Growth
While many people believe tree roots grow deep into the ground, the exact opposite is true. The majority of tree roots are found in the top 12 inches of soil. When these shallow growing roots get big enough, they can break through growing above the surface. Poor soil conditions accelerate this process. Also, some soil erode over time, leaving the roots even more exposed.
Recommendations for Surface Roots in the Lawn
1. Some root cutting can be done but keep it to a minimum
If the roots are smaller or only have a few present, cutting them can be an option. However, remember the roots are holding the tree in place and are the main stability for the tree. Also, feeder roots are supplying the tree with nutrients and water. The more roots are cut, the larger the negative impact on tree health and stability.
2. Leave big roots alone
Cutting larger roots will have a big impact on tree health, stability and can open up the tree to disease and insect issues.
3. Apply a LIGHT amount of black dirt and seed (some conditions)
If a small amount (depth) of soil can handle the situation (instead of cutting roots), then proceed with covering the roots with a light amount of soil (no more than 2 inches). However, it must be understood that adding soil over roots CAN suffocate the roots just like poor soil. Some tree types are very sensitive to adding soil. As little as 2 inches of added soil can severely impact some trees, even causing heavy decline and death.
4. Add wood mulch
It is obviously not always practical, but adding mulch over the roots is the best option. Since trees are grass are natural enemies, planting groundcover or other perennials would be a more favorable option.
5. Leave the roots alone
If there is no safety or major nuisance, it is often best to leave the roots alone. It is likely that no matter what is done, more surface roots will develop.
