Post Helene: Tips on Erosion Management
Hurricane Helene triggered over 300 landslides in Buncombe County last fall. Even when slopes were spared, the storm caused significant erosion, increasing the likelihood of future landslides. Soil erosion–the detachment of the nutrient-rich upper layer of earth known as topsoil–reduces soil productivity and increases water runoff. While landslide reparation is a job best left to professionals, you may be able to tackle less severe erosion on your own.
Slope stabilization
Begin by assessing the steepness of your slope, usually described in degrees or percentages. Slopes need to be less than 45 degrees or angled below 12% for plants to take root. Both iPhones and Androids now have apps available for measuring slope steepness (search for “inclinometers”).
It is not necessary to replace topsoil before planting. According to Buncombe County Cooperative Extension Agent Michael Rayburn, recreating topsoil that replicates pre-Helene is very difficult. Instead, he recommends growing plants directly in the remaining subsoil, adding compost or other organic matter to improve soil quality.
Terracing
Terracing reduces a long slope into a series of shorter, level gardens, much like a staircase. The steps are created by constructing mini-retaining walls with wood, brick, or stone–see this pamphlet for more information.
Many homeowners in our mountains choose to terrace steep landscapes rather than attempt to garden on slopes. Although a time-intensive strategy for managing erosion, terracing can be a solution for slopes too steep for planting and a visually appealing means of reducing water runoff.
Garden design
Whatever strategy you choose for mitigating erosion, fully plan your garden design before you begin. Resist the temptation to toss random–or worse yet, invasive–seeds into the dirt.
If you have exposed areas in your landscape and are pressed for time this year, choose a temporary cover crop. Rayburn notes that cover crops help stabilize soil, prevent erosion, and improve soil health while providing time for bare spots to “rest and…recover so they can be useful for you in the future.”
Plant selection
Native plants—adapted to regional soils, slopes, and climate—are best for quickly reestablishing an area. In addition, native plants benefit pollinators, which is important given that the destruction of trees during Helene likely left insects with fewer habitats.
Ornamental native grasses can be especially helpful in stabilizing slopes. For example, switch-grass (Panicum virgatum) has roots that extend up to three feet deep, very effectively holding soil in place. See this article for a full list of recommended native grasses and additional suggestions for native plants that do well on slopes.
Live staking is a strategy for managing erosion that has traditionally been used in stream bank repair. It involves inserting native tree or shrub cuttings (“live stakes”) that are two to three feet in length directly into the ground during the dormant season (November to March). The stakes grow root systems that stabilize soil and prevent further erosion.
In our region, common live stake choices include elderberry (Sambucus canadensis) and ninebark (Physocarpus opulifolius). Additional species recommended for North Carolina can be found here.
Article written by Melissa Himelein, Extension Master GardenerSM Volunteer.
For more information:
Erosion management
– Slope Stabilization (contains list of native grasses, wildflower mixes, and trees and shrubs)
– Erosion and Sediment Control (resources from the NC Environmental Quality Erosion and Sediment Control Program)
– Soil Health Post Helene (webinar on WNC soil conditions)
Resources on landslides
– Landslides in Western North Carolina (information about landslides across the region and resources regarding risk reduction)
– Landslide Basics (introductory information about landslides from the US Geological Survey)
Terracing and live staking
– Terracing (step-by-step guide to building a terrace)
– Live Staking for Stream Restoration (introduction and instructional guide)
– Live Stake Descriptions (five recommended livestakes in NC)
– MountainTrue FAQ: Live Staking (information about live staking from local WNC nonprofit focused on environmental issues)