Hillside Erosion Control: Plants & Methods

A bare slope sheds water fast, and every storm carries soil downhill — rilling the surface, undercutting plantings, and dumping mud onto whatever sits below. Erosion control on a hillside comes down to two jobs done together: slowing the water down so it soaks in instead of running off, and holding the soil in place with roots and physical structure until vegetation takes over. No single product does both on a steep grade. This guide walks through how to read your slope, the deep-rooted plants and groundcovers that anchor soil, the structural methods (terracing, retaining walls, riprap), the erosion-control blankets and mats that protect bare ground while plants establish, and how to combine them based on how steep the hill actually is.

Read the slope before you choose a method

Slope steepness is usually written as a ratio of horizontal run to vertical rise — a 3:1 slope drops 1 foot for every 3 feet of run (about 18°), while a 2:1 slope drops 1 foot for every 2 feet (about 27°) and a 1:1 slope is a 45° face. The steeper the grade, the faster water moves and the harder it is for plants alone to hold soil. As a rough guide: slopes gentler than 3:1 can usually be handled with dense planting and a blanket; slopes between 3:1 and 2:1 need plants plus erosion matting and often some terracing; slopes steeper than 2:1 generally require structural help — terraces, retaining walls, or riprap — combined with planting.

Also note where the water comes from. A slope that only sheds its own rainfall is far easier than one collecting runoff from a roof, driveway, or upslope yard. If concentrated flow is the problem, the fix often starts at the top — a swale, French drain, or downspout extension to divert and disperse water before it ever reaches the slope face.

Plants that anchor a slope

Vegetation is the most durable, lowest-cost long-term solution because living roots knit the soil into a mat and the canopy intercepts raindrops before they dislodge particles. The trick is choosing plants with the right root habit and planting them densely. Aim for a mix of deep-rooted anchors and spreading groundcovers so you cover both the surface and the subsurface.

Deep-rooted and clumping plants (the anchors)

• Native bunchgrasses: little bluestem, switchgrass, and prairie dropseed send roots several feet down and hold steep banks superbly.
• Shrubs with strong root systems: fragrant sumac (Rhus aromatica ‘Gro-Low’), bayberry, snowberry, and native dogwoods (red-osier) spread by suckers and lock in soil.
• Deep-rooted perennials: butterfly weed, false indigo (Baptisia), and prairie coneflowers have long taproots.
• Willows and dogwood live stakes: on wet banks and streamsides, dormant cuttings pushed into the soil root readily and create instant reinforcement.

Spreading groundcovers (the surface cover)

• Creeping juniper (Juniperus horizontalis): tough, evergreen, drought-proof, excellent on hot, sunny banks. Zones 3–9.
• Cotoneaster, creeping rosemary, and trailing rosemary for sunny slopes.
• Liriope (lilyturf) and dwarf mondo grass for shaded banks; their fibrous roots hold soil well.
• Creeping phlox, ajuga, and creeping thyme for color on gentler grades.
• Vinca, pachysandra, and English ivy for shade — effective but choose carefully, as ivy and vinca can be invasive in some regions.

Plant densely. Close spacing — say 12–18 inches for groundcovers and 24–36 inches for shrubs — closes the canopy and root network in one to two seasons instead of three or four, which is the difference between a slope that holds and one that keeps washing during establishment. Plant on the contour, dish each planting hole slightly inward to catch water, and mulch heavily between plants. For broader plant-selection ideas across your property, browse our outdoor living and landscaping guides.

Erosion-control blankets and mats

Plants take a season or two to establish, and a bare slope can erode badly in the meantime. Erosion-control blankets bridge that gap by armoring the surface, holding seed and soil, and retaining moisture for germination. Lay them over freshly seeded or planted ground, anchor with landscape staples every 1–3 feet (more on steep ground), and overlap seams shingle-style so water can’t get underneath.

• Straw and straw/coconut (coir) blankets: biodegradable, ideal over grass or wildflower seed on moderate slopes; the netting and fiber rot away as plants take over.
• Jute netting and coir logs: open-weave natural fiber for gentler slopes and as toe protection along the base.
• Coconut (coir) mats: longer-lasting (2–4 years) for steeper or wetter sites that need more time to vegetate.
• Turf reinforcement mats (TRMs): permanent synthetic matting for severe slopes and channels with concentrated flow, where vegetation alone can’t survive the velocity.

For seeded slopes, a heavy mulch of weed-free straw or wood-fiber hydromulch tacked down does much of the same job at lower cost on gentle grades. Whatever you use, the goal is the same: keep raindrops from hitting bare soil and keep seed from washing away until roots take hold.

Structural methods for steep slopes

Once a slope exceeds about 2:1, or where space is tight, you usually need to physically reshape or hold the grade.

Terracing

Terracing breaks one long, fast slope into a series of short, level steps, each of which catches water and gives plants a flat bed to root in. You can build low terraces with timber, boulders, or interlocking concrete blocks, or simply grade a series of broad benches. Terracing dramatically cuts runoff velocity and is one of the most reliable fixes for a steep, eroding bank that you also want to plant.

Retaining walls

A retaining wall holds back a vertical or near-vertical cut. Segmental block walls under about 3–4 feet are a common DIY project; anything taller, or any wall holding back a structure or a saturated slope, should be engineered and may require a permit and proper drainage (gravel backfill and weep holes or drain pipe behind the wall). Skipping the drainage behind a wall is the most common cause of failure — water pressure builds and pushes the wall out.

Riprap and rock

Riprap — a layer of angular rock over filter fabric or a gravel base — armors slopes against concentrated flow, such as drainage channels, culvert outlets, and pond or stream banks. It’s purely functional but bulletproof where moving water would tear out plants and matting. Use it at the toe of a slope or in flow channels, and vegetate the calmer areas around it.

Putting it together by slope grade

Gentle slope (gentler than 3:1): dense groundcover and deep-rooted plants plus a straw/coir blanket or heavy mulch is usually enough. Moderate slope (3:1 to 2:1): add coir matting or jute netting, plant shrubs and bunchgrasses on the contour, and consider a couple of low terraces or a swale at the top to divert runoff. Steep slope (steeper than 2:1): lead with structure — terracing, a retaining wall, or riprap in flow paths — then plant the benches and faces densely and cover with longer-lived coir or turf-reinforcement matting. In all cases, divert concentrated water away from the slope first, and remember that soil type matters: loose sandy ground erodes faster, so check our notes on amending sandy soil if your bank is light and free-draining. For the low-traffic faces, a tough living carpet works well — see our no-mow lawn and groundcover guide for plant ideas.