A steep hill that is too dangerous or difficult to mow is a liability. Uncontrolled slopes are highly susceptible to soil erosion, where water runoff and gravity rapidly strip away topsoil, leading to deep channels and instability. Converting this difficult terrain requires replacing turfgrass with specialized, low-effort plantings. This solution is a form of living engineering designed to stabilize the soil mass permanently.
Prioritizing Function: Soil Stabilization and Erosion Control
The primary function of any plant chosen for a steep slope is to physically anchor the soil and mitigate the destructive forces of water runoff. Stabilization relies heavily on the plant’s root architecture. The most effective plants develop a two-part root system: a dense, fibrous mat and deeper anchoring roots.
The fine, fibrous roots near the surface interlock with soil particles to form a cohesive mat, preventing the top layer of soil from washing away during heavy rainfall. This matting effect binds the soil mass together, acting as a natural mesh. Deeper, thicker roots then penetrate the slope to act as underground buttresses, securing the soil profile to the subsoil or bedrock.
Above the ground, the plant canopy performs a secondary function by intercepting raindrops. When rain hits bare soil, the impact dislodges particles, initiating erosion. A dense layer of leaves and stems slows the water’s velocity, allowing it to drip gently to the ground. This increases the soil’s absorption rate and reduces destructive surface runoff.
Low-Maintenance Planting Solutions
Selecting the correct plant types means choosing species with aggressive, spreading habits that quickly cover the ground and minimize open soil exposure. These plants must also be hardy to withstand the challenging conditions of a slope, which often include rapid drainage, poor soil, and intense sun exposure.
Vigorous, Spreading Groundcovers
Groundcovers are the first line of defense, forming the dense root mat that protects the topsoil layer. Vinca minor (periwinkle) is a popular choice due to its evergreen foliage and ability to thrive in both sun and shade, spreading rapidly via trailing stems that root as they travel. Pachysandra terminalis is another reliable option, well-suited for shaded hillsides, forming a carpet of glossy green leaves that suppress weed growth. For sunny, dry areas, various Sedum species, such as ‘Angelina’ stonecrop, offer drought tolerance and succulent foliage, making them resilient in rapidly draining soil.
Low-Growing, Sprawling Shrubs
Low-growing shrubs provide deeper root penetration and more bulk than groundcovers, adding stability and structure. Juniperus horizontalis (creeping juniper) is an evergreen conifer with a wide, sprawling habit and robust root system that anchors large areas of soil. Cultivars like ‘Blue Rug’ spread laterally, providing year-round coverage and requiring minimal pruning. Cotoneaster horizontalis (rockspray cotoneaster) is another excellent woody plant, offering a dense, fishbone branching pattern that hugs the ground. Its stems root where they touch the soil, creating multiple points of attachment for greater stability.
Native Grasses and Herbaceous Plants
Native grasses and clumping herbaceous plants offer exceptionally deep, fibrous root systems effective at binding soil. Schizachyrium scoparium (Little Bluestem) and Panicum virgatum (Switchgrass) are hardy, drought-tolerant native grasses whose root masses can reach several feet deep, creating an extensive underground network resistant to erosion. Liriope spicata (creeping liriope), while not a true grass, is often used for its grass-like appearance and clumping root structure, which holds soil firmly in place.
Installation and Establishment Techniques for Slopes
Successful establishment on a steep grade requires techniques that counteract the effects of gravity and water runoff before the plants take root. Planting should always be done by hand using small plant plugs or containers to minimize soil disturbance, avoiding any tilling that would loosen the ground.
When planting, set the crown of each plant slightly higher on the slope side of the hole. Gently mound the soil on the lower side to form a small, crescent-shaped basin. This basin acts as a localized check dam, designed to capture and hold water long enough to soak into the root zone instead of immediately running down the hill. All plants should be staggered in a triangular pattern rather than straight rows, which helps break up the path of water flow.
Immediately after planting, the slope must be covered to prevent soil wash-out until the roots mature. Biodegradable erosion control blankets, typically made of coconut coir or jute netting, should be pinned directly over the soil to provide instant stability. If using mulch, shredded wood or bark is preferable to chips, as its interlocking texture is less likely to slide down the hill. Watering is best accomplished with drip irrigation or soaker hoses, allowing for slow, deep saturation without creating the surface runoff that overhead sprinklers often cause.