Which Slope Plants Does NC State Actually Document for Erosion?

Search for plants to hold a bank and you will get a dozen confident lists. Almost none of them tell you where the claim comes from.

That matters more than it sounds, because in the NC State Extension Plant Toolbox an erosion claim can come from three quite different places, and they are not equally strong.

The three grades

1. The tagged attribute. The structured “Resistance To Challenges” field lists Erosion. This is a categorised, searchable attribute — the strongest thing the Toolbox says about a plant.

2. The placement field. The “Landscape Location” field includes Slope/Bank. This is a statement about where the plant belongs, which is different from, and complementary to, a resistance claim.

3. The description. A sentence in the page prose recommends it for banks. Useful, but it is a recommendation in words rather than a tagged attribute.

Most plant lists silently merge all three. We think the difference is worth printing.

The two best-documented plants

Downy serviceberry and fragrant sumac each carry Erosion in the structured field and Slope/Bank in Landscape Location. Fragrant sumac's page goes further in prose: it is “excellent for stabilizing banks and slopes” and “frequently used on embankments to stabilize the soil.”

Three independent statements on one page. If you are planting one thing on a dry Piedmont bank and want the best-documented option, fragrant sumac is it — but note the width. NC State prints it at 6 to 10 feet across. It is a spreading colonial shrub, which is precisely what you want holding a bank and precisely what you do not want three feet from a path.

The one that surprises people

Little bluestem is the grass everyone reaches for on a dry bank. It is a fine plant, native, tough, and beautiful in autumn.

Its Toolbox resistance line reads: Black Walnut, Deer, Diseases, Drought, Dry Soil, Heat, Humidity, Insect Pests, Pollution.

Erosion is not on that list.

That does not mean it fails on a slope. It may well hold soil perfectly adequately — plenty of practitioners use it that way. It means that if your standard is documented erosion performance, little bluestem does not meet it, and a list that includes it without saying so is quietly relaxing its own rule.

Wax myrtle sits one grade below that again: its page recommends it “on a bank for erosion control” in the description, but Erosion is absent from the structured field and Slope/Bank is absent from Landscape Location. Words on the page, nothing tagged.

What plants can and cannot do

Now the part that matters more than the species list.

Plants control surface erosion. They do not hold a failing slope. Roots bind the top several inches against sheet flow and raindrop impact. They do nothing about a slope that is moving as a mass, and nothing about concentrated water arriving from somewhere else. If you have a slope with a scarp at the top, or a bulge at the toe, or cracks running across it, that is a stability question and it needs an engineer, not a plant list.

Getting them established is the whole problem. A bare bank is at its most vulnerable in exactly the period before the plants root in. That first season is what erosion control fabric, coir netting and heavy mulch are for — they buy time. Plant in autumn if you can, so roots get a cool damp season before their first summer.

Do not till a slope. Loosening the surface of an erodible bank before a rain event does the opposite of what you want. Plant into individual holes and leave the rest of the surface intact.

A note on the rules

Erosion and sedimentation rules in North Carolina turn on land-disturbance thresholds, and there is a widely repeated myth that they only apply above one acre. If you are doing anything substantial to a slope, that is worth checking before you start — we have written about it separately.

The drawn version

Our Erosion Control Slope Planting Plan is a 40 ft × 22 ft bank drawn to scale at mature spread — 70 plants, 7 species — with the erosion evidence for every species graded and labelled rather than merged, plus the plants we left out and exactly why.

Not a design for your property, not an engineered drawing, and not a stormwater design. If your slope has signs of mass movement, get a professional engineer. Alex Purdy is a licensed North Carolina landscape contractor (CL.1872) and holds NCSU SCM Inspection & Maintenance certification #5970; he is not a professional engineer and not a registered landscape architect.