How Do I Recover Tree Roots Exposed by Erosion?

“I have tree roots that have been exposed near the ground because of soil erosion.  Should I try to recover with soil or leave it be?  Will it kill the tree? I think they are the roots of a very large willow oak.  There is also a very large poplar tree close by, too.” Question from Richard of Winston Salem, North Carolina

Answer: Extensive root exposure can be damaging to trees, so I recommend restoring the eroded area. Exposed, large woody roots are not a problem, but the broad exposure of smaller feeder roots can cause trouble and indicates a severe erosion problem.

Different trees can tolerate different levels of root-soil cover. Willow oak (Quercus phellos) has a shallow root zone and should not be covered with a thick layer of soil. Two to three inches of soil over the layer of smaller roots should be enough. Poplars have large, extensive root systems and are less prone to damage from high levels of erosion. Still, erosion is always troublesome in the landscape and should be stopped. It can also cause tree instability and make them far more prone to falling during storms.

Here are my recommendations for managing your erosion and tree-root exposure problem.

  1. Identify and attempt to stop the source of erosion. If you can identify the water source, you can often divert the water. Your method of diversion would depend on the source. Feel free to provide more information regarding the source, so I can provide specific solutions.
  2. Cover the exposed feeder roots with at least 2 to 3 inches of topsoil and press it down. We also recommend mixing a good organic amendment into the topsoil, such as Black Gold Canadian Sphagnum Peat Moss.
  3. Apply a straw mat or burlap erosion mat to keep the soil in place.
  4. Plant plugs of groundcover for dry shade between the matting. A good groundcover layer will hold the soil in place as it becomes established (list below).
  5. Keep the plugs watered and cared for until they begin to really grow and spread–around two to three months.

There are lots of good groundcovers for dry shade that reduce or stop erosion. These include creeping wire vine (Muehlenbeckia axillaris ‘Nana’, light shade, Zones 6-10), evergreen vinca (Vinca minor, shade, Zones 4-9), dwarf mondo grass (Ophiopogon japonicus ‘Nana’, shade, Zones 6-11), golden sweet flag (Acorus gramineus ‘Ogon’, shade to part shade, Zones 5-11), and the evergreen creeping plum yew (Cephalotaxus harringtonia ‘Prostrata’, Zones 6-9), which I highly recommend.

If you like native groundcovers, consider wild ginger (Asarum canadense, shade, Zones 3-8), Allegheny spurge (Pachysandra procumbens, shade, Zones 4-9), and the pretty green-and-gold (Chrysogonum virginianum, part sun to shade, Zones 5-8).

I hope that these solutions help!

Jessie Keith

Black Gold Horticulturist

Get an Edge on Porous Paving

Short, dense perennials are the ultimate edge plants to tidy up after repairs to eroding edges.

Artists learn early on that the most important parts of a line are the beginning and end points.  The quality of the start and end define the line’s value. No matter how light the line weight is between the two points, the line continuum will stay intact because the viewer will naturally extrapolate by filling in a missing or faint center.

This essential working element of design also applies to gardens and landscapes, with garden edges setting the lines that define the flow and focal points of a given space. But, smart landscape and garden designers also consider the functionality of garden edges.

Path and Patio Edge Problems


“New” porous patios and paths have become popular because they facilitate ground drainage, but they can also have hidden design flaws. The trend to design patios that enhance drainage has placed emphasis on the patios rather than the gardens that frame them.  The truth is that the most important part of a garden composition is how well the planting line meets a gravel, flagstone, or paver area.  A close edge planting is often omitted in porous paving plantings, which leads to erosion and disrupts the visual flow of the design, causing structural and visual disarray for everyone to see.

Every time it rains, particles will flow onto the flagstone and into the pool beyond.

Unplanted edges and paving gaps are subject to tremendous erosion caused by hard rains powerful enough to dislodge gravel and surface soil particles.  The porous fill flows away with runoff and settles out on low ground.  The greater the impact of each raindrop, the more soil is lost, creating washout spots, gaps, and hidden cavities under stones.  Erosive rains can also undercut the units or frames that hold edging stones in place, creating a double-foot-traffic hazard for tripping.

Once porous paving starts having these problems, impacted plantings may fail to thrive or die, and your pavers may become loose and unsteady.  Gravel has traveled and thinned at the edges.  Low muddy spots have become a mess and hazard.  Getting that patio created was just half the battle.  What they didn’t tell you is that unlike solid paving (lay it and forget it), porous paving requires well-planted edges and a little more maintenance.

Plant Your Edges!


Planting low plants like thyme among pavers can also reduce erosion and add to the beauty of a porous patio.

Use the mild fall weather to rehabilitate your porous patio and path edges with beautiful plantings that control erosion. Here’s the process:

  1. Fill low edge spots and pack cavities below pavers or flagstones with natural soil blended with 20 percent Black Gold Garden Soil. Shoot for a soil level at least 1 inch below the top surface of your stones to keep them high and dry.
  2. Regrade all peripheral soil beyond the garden edges, so it’s not draining back onto the patio when you water. Reset any pavers or flagstones that have shifted or tilted.
  3. Set your plants along the edges in pleasing designs that consider height and flowering time as well as cultural needs. Choose dense edge plants to hold the soil in place where it has washed out before. Enrich planting holes with more Black Gold Garden Soil to encourage quicker establishment of plants.
  4. Apply gravel, attractive rock, or dense organic mulch over the top of any exposed soil after planting. This protects against future surface erosion every time it rains.

Edge plantings slow runoff to limit erosion along and below the most vulnerable, outermost paving materials.  Their established roots also reduce gravel creep.  The right plants for this scenario are low and dense, deep-rooted, and hardy.  They should be selected for the exposure of your garden space, be it sun or shade.  Most of all, avoid short-lived, easily damaged species, or those with spines and thorns – all unsuitable for this condition.

Once your garden plantings around your porous patio are dense enough, they will protect it from washout, whether the porous material is recycled antique brick mosaic or pea gravel.  Just remember, when it comes to porous paving, begin with the edges, and the rest will take care of itself.


“Nest” perennial plantings along the edge to hold soil and gravel and reduce erosion.