Roots belong underground, right? Most of the time, yes. And most of the time, if a plant’s roots are exposed to light, they’ll grow away from it and go back into the ground or mulch to protect themselves from that light. So why do some tree roots grow at or slightly above the soil surface where they can trip people, mess up equipment, buckle sidewalks and driveways, look out-of-place and unattractive, and generally drive homeowners and grounds managers to cover, smother or chop them?
Roots that have been exposed by erosion can be covered lightly with mulch.
Photo Credit: Bonnie Lee Appleton
Paved-over roots can burst to the surface, buckling paving and causing a tree to die.
Photo Credit: Bonnie Lee Appleton
The thing is, roots are opportunistic – growing wherever they find soil with adequate space, oxygen, water and nutrients. That’s generally in the top few inches to top few feet of soil, depending on soil type and compaction. (They go shallower in compacted clayey soils, but deeper in uncompacted sandier soils.)
Roots are also easily directed. If they hit something they can’t penetrate, like rocks, foundations, paving, pipes and other hard objects, they’ll be deflected. But if these supposedly nonporous objects have holes or cracks in them – and if those holes or cracks offer paths of least resistance, and if those holes or cracks provide paths to soil with adequate oxygen and moisture – then that’s where the roots will grow. That’s how roots end up in pipes, as well as cause cracks and buckling to sideways, driveways, roads and other paved surfaces.
As trees grow aboveground, you’ll see the trunk getting taller and wider each year. Likewise, roots growing underground grow bigger – such that over time some of the shallowest roots may simply grow large enough to break the soil surface. Combine normal root growth with soil erosion, and you’ll see lots of roots – especially on hills, riverbanks and aboveground.
So what do you do about those pesky roots popping up in your yard? Should you cover the offenders?
Yes and no. Riparian species – those that grow along bodies of water, such as river birches, sycamores, pin and willow oaks, and red maples – are tolerant of some fill over portions of their roots, but people tend to overdo the “some” part. Generally, you should avoid covering roots if what you intend to cover them with is soil. While an inch or two of soil atop just a few roots won’t kill a tree, many trees species are very sensitive to soil level changes, including natives like beeches and white oaks. It’s best just not to do it.
A better solution for dealing with surface roots is to cover them with mulch. Any mulch will do, from recycled wood chips to pine bark and needles, but just 2-3 inches of it – no mulch volcanoes!
Another suggestion often offered when it comes to covering surface roots is to plant groundcovers around them. This solution may or may not help the situation. If only a small portion of the roots will be damaged or impacted in any one year as the groundcover planting holes are dug, and if the groundcover is perennial, then this solution is generally acceptable.
Surface roots can be problematic to people and equipment, but without a good healthy root system, your trees can’t survive and grow well. Covering roots is one way to deal with them but only if the covering (preferably mulch) is shallow and porous, allowing water and gases to be exchanged between the air and soil.