AMES, Iowa – Trees are an essential part of any landscape, but their roots can create issues. How can surface and shallow roots affect their surroundings? Is construction a problem?
Iowa State University Extension and Outreach horticulturists can help answer questions about how to best handle tree roots.
How deep is a tree’s root system?
A majority of a tree’s roots are located in the upper 12 to 18 inches of soil. While tree roots are shallow, they extend a considerable distance from the tree trunk. A tree’s root system may extend out two to three times the distance from the trunk to the dripline (the outermost edge of the tree’s canopy).
There are several large surface roots around my maple tree. Can I cover the roots with soil?
Trees have shallow roots. As the tree roots grow, some of the larger roots near the soil surface may emerge from the ground. While most individuals regard surface roots as unwelcome, they are normal for many trees (especially maples).
It’s usually best to ignore surface roots as much as possible. (Granted, mowing around surface roots can be tricky.) Covering the area around the tree with 1 to 2 inches of soil provides only temporary relief. The roots will continue to grow and will probably reappear in a few years. Placing four or more inches of soil around a tree may damage or destroy the tree by depriving some of the tree’s roots of oxygen.
If you’re not fond of mowing around the tree roots, you can remove/destroy the turf and apply mulch around the tree. Wood chip or shredded bark mulches are actually beneficial to trees. An appropriate mulch depth for areas around trees is 2 to 4 inches. Shade tolerant groundcovers, such as hostas, creeping lilyturf, wild ginger and barrenwort, also could be planted around the tree.
What effects will construction activities have on nearby trees?
Construction of buildings, patios, garages, driveways, sidewalks and roads often compromises the growing environment of nearby trees. The majority of a tree’s roots are located in the top 12 to 18 inches of soil and often extend well beyond the edge of the tree canopy (dripline). Changing the grade by removing or adding soil around existing trees can cause extensive root damage. Removing soil can disturb and injure many of the tree’s roots. Adding soil can reduce the movement of oxygen to tree roots, causing them to die.
Trenching often severs major portions of the tree’s root system. Soil compaction by heavy equipment and foot traffic reduces the supply of oxygen to the root system. Mechanical damage to the trunk of a tree caused by construction equipment can strip off bark and damage vascular tissue, reducing nutrient and water movement in the tree. Open wounds created by these injuries can serve as entryways for insects, diseases and decay-causing fungi. Severe construction damage may cause affected trees to decline and die.
The best way to minimize damage to a tree during construction is to do nothing around or on top of a tree’s root system. Construct a sturdy fence at least at the outer dripline of the tree and allow zero activity within this area. Prohibited activities inside the dripline of the tree include lowering the grade, adding soil, trenching, parking or operating machinery in the area, and storing supplies, soil or excavation materials.