Planting on a slope presents a unique challenge where gravity works against plant establishment and soil retention. Slopes exceeding a 3:1 ratio (a one-foot vertical rise for every three feet of horizontal run) require special attention to prevent rapid soil loss. The primary goal is two-fold: to establish deep-rooted vegetation and to minimize the movement of soil and water down the incline. Achieving this requires physical slope preparation, strategic plant selection, and specialized planting techniques to counteract gravity and runoff.
Preparing the Slope for Stability
Before any planting begins, the slope must be stabilized to minimize immediate soil erosion and create a favorable environment for new roots. On slopes between 33% (3:1) and 50% (2:1) grade, temporary erosion control measures are necessary. Erosion control blankets, such as jute netting or biodegradable fiber mats, physically hold surface soil in place during heavy rainfall until the plants take root. These mats are rolled parallel to the slope’s contour and secured with biodegradable stakes, allowing vegetation to grow directly through the mesh.
For slopes with longer, unbroken runs, sediment control devices called wattles can be deployed. These are dense, tube-shaped logs made of coir or compressed straw that are staked into shallow trenches along the contour lines of the slope. Wattles act as miniature check dams, slowing runoff velocity and filtering sediment, which prevents the formation of erosive rills and gullies.
Proper soil preparation is paramount, as slopes naturally drain quickly and often consist of disturbed, nutrient-poor subsoil. Incorporating two to three inches of compost into the top layer improves the soil’s structure and water-holding capacity. This amendment gives young plants access to moisture and nutrients, which are often scarce on steep, exposed hillsides.
Selecting the Best Plants for Erosion Control
The selection of plants for slope stabilization depends on the strength and type of their root systems. The most effective plants feature a dense, fibrous root system, consisting of many thin, branching roots that spread horizontally to form a cohesive mat near the soil surface. This structure is superior for binding topsoil and preventing shallow erosion caused by rainfall and surface runoff.
Plants with a deep taproot system provide excellent long-term structural anchoring, helping to prevent deeper-seated issues like mass wasting. A combination of plant types is most beneficial, utilizing groundcovers and grasses for surface binding and deep-rooted shrubs for structural integrity. Suitable choices include:
- Dense groundcovers like creeping juniper, which spreads rapidly and forms multiple anchor points where its branches contact the soil.
- Low-growing shrubs such as certain varieties of cotoneaster, which have extensive lateral roots that hold significant amounts of soil.
- Native grasses, including switchgrass and fescue, whose root networks penetrate several feet deep while their foliage buffers the impact of raindrops.
- Drought-tolerant species that thrive in drier conditions to ensure long-term survival.
Specialized Planting and Irrigation Methods
The physical act of placing plants into a steep slope requires a specialized technique to ensure stability and water retention. The root ball should be positioned so the plant is angled slightly uphill toward the top of the slope. This orientation helps to prevent the plant from being pushed out of the soil by gravity or washing away during heavy rain.
As you backfill the planting hole, soil should be mounded up on the downhill side of the plant, creating a small, crescent-shaped basin or berm. This miniature terrace captures and holds water near the root zone, allowing moisture to soak in rather than immediately running off. Plant spacing should be denser than typical level-ground installations to achieve rapid canopy coverage and root interlocking, which accelerates the stabilization process.
Effective irrigation is crucial for establishment but must be managed to avoid inducing new erosion. Overhead sprinklers should be strictly avoided, as their forceful spray dislodges soil particles and creates immediate runoff. The preferred method is a low-volume system, such as drip irrigation or soaker hoses, installed along the contour lines. This setup delivers water slowly and directly to the root zone, maximizing infiltration and minimizing surface disturbance. Placing the drip emitters inside the small, uphill-angled berms ensures water is retained long enough to be absorbed by the newly planted roots.