Hillside erosion occurs when water runoff, wind, or gravity displace soil particles, leading to the loss of topsoil and potentially damaging property foundations. Slopes are vulnerable because water moves faster downhill, accelerating the removal of loose soil. The most effective, long-term solution for stabilizing these inclines is the strategic use of deep-rooted vegetation. Plants anchor the soil with their root systems and slow the flow of surface water, preventing the formation of erosive channels or gullies.
Preparing the Slope for Planting
Before planting, assess the slope’s steepness, soil type, and drainage patterns. For excessively steep slopes, minor re-grading or the construction of terraces using large rocks can create gentler planting areas. This helps slow concentrated water flow that could wash away new plantings.
Clearing the area of debris and invasive weeds is important, as they compete with new plants for resources. If the slope is actively eroding, temporary stabilization measures are needed until root systems establish themselves. Biodegradable materials, such as erosion control blankets or straw wattles placed perpendicular to the slope, provide immediate protection against rainfall impact. These materials decompose over time as the permanent vegetation takes hold.
Essential Characteristics of Erosion Control Plants
A plant’s effectiveness on a slope is determined by its subterranean root system, not its appearance above ground. Erosion control plants must possess dense, fibrous roots that form an interlocking mesh, binding soil particles together. This extensive root network provides the tensile strength needed to resist water runoff and gravity.
Deep-rooted plants, such as native grasses, can extend their roots six to twelve feet into the ground, offering superior anchoring. Aggressive, low-growing habits are beneficial because they quickly create a continuous carpet that shields the soil surface from raindrops. Plants must also exhibit high drought tolerance, since water runs off slopes quickly, leaving upper soil layers drier.
Recommended Plant Types for Hillside Stability
Selecting a variety of plant types creates a layered defense system that stabilizes the soil at multiple depths. Native species are often the best choice, as they are adapted to the local climate and require less maintenance once established. Combining groundcovers, grasses, and shrubs provides comprehensive coverage from the surface down to the deep subsoil.
Groundcovers
Groundcovers spread rapidly to cover bare soil, immediately reducing the impact of rain and wind erosion. Popular choices include Creeping juniper (Juniperus horizontalis) and Rockspray Cotoneaster (Cotoneaster horizontalis), which root wherever their branches touch the ground. For shaded slopes, evergreen perennials like Sweet Box or drought-tolerant options like Thyme offer dense surface coverage.
Grasses and Sedges
Ornamental grasses and sedges are powerful erosion fighters due to their vast, fibrous root structures. Native grasses like Switchgrass (Panicum virgatum) and Little Bluestem (Schizachyrium scoparium) develop deep roots that stabilize soil on steep grades. Sedges, such as Pennsylvania sedge (Carex pensylvanica), form dense, shallow mats that work well for surface-level binding, especially in partially shaded areas.
Shrubs and Small Trees
Hardy shrubs and small trees provide structural stability with strong, lateral root systems that spread horizontally. The weeping form of Forsythia (Forsythia suspensa) and suckering shrubs, like Aronia (chokeberry), are effective because they naturally colonize an area. These woody plants offer a long-term solution by anchoring the slope with thicker, more permanent roots.
Successful Planting and Establishment Techniques
Planting on a slope requires a deliberate approach to maximize establishment success and prevent washout before roots develop. Plants should be set at a higher density than on flat ground, ensuring root systems merge faster to create a continuous soil-binding mat. Use a staggered pattern instead of straight lines to prevent water from channeling and gaining velocity down the hill.
When setting plants, the crown should be slightly tilted back toward the hill. This directs water toward the root zone rather than allowing immediate runoff. After planting, use slow, deep watering to encourage roots to grow downward. Drip irrigation or soaker hoses are the most practical choice, as they deliver water slowly without causing surface runoff.
Mulching is important for moisture retention and protection. Heavy, coarse-textured mulches, such as shredded bark or wood chips, are preferred because they interlock and resist being washed away. A layer approximately one to one and a half inches thick is sufficient to protect the soil surface without inhibiting new growth.