To xeriscape a slope, slow the water down and hold the soil in place: terrace or key in boulders across the grade, plant deep-rooted shrubs and bunchgrasses densely, cover bare soil with angular gravel or erosion netting while plants establish, and water with drip lines run across the slope instead of spray. A slope is the rare case where the low-water approach isn't just cheaper to run but structurally better. Lawns fail hardest on hills: mowing is dangerous, sprinkler water sheets off before it soaks in, and every storm carries more topsoil to the sidewalk. A well-built xeriscape turns all three problems around.
Why slopes shed water, and how to stop it
On a grade, rain and irrigation run downhill before they soak in, so the top of a slope stays dry, the bottom stays wet, and moving water carries soil with it. CSU Extension's erosion guidance puts the fix simply: plant roots stabilize the soil, and stems and leaves slow the water to give it time to percolate. Every technique below does one of those two jobs. Do both and the slope largely takes care of itself.
Shape the slope first
Terrace the steep sections. A few low retaining walls of dry-stacked stone, block or timber turn one erosive slope into flat, plantable steps. Two short walls beat one tall one: they're easier to build, drain better and look less like a fortress. Taller walls often need a permit and engineering, so check with your building department before you build anything more than knee-high.
Key in boulders. Bury large rocks a third to half deep in staggered rows across the slope, never in straight lines down it. They act as check dams, create planting pockets and look geological. This is rock garden design doing double duty as engineering.
Cut planting basins, not shelves. Behind each boulder and each plant, shape a small crescent-shaped basin, a flat cup on the downhill side that catches water and gives roots time to drink.
Route the big flows. If the slope catches roof runoff or a neighbor's drainage, give that water a channel. A dry creek bed running diagonally across the grade takes the destructive flow out of the planting.
Pick your approach by slope
| Situation | Best approach |
|---|---|
| Gentle grade you can walk and work on easily | Plant directly; crescent basins, gravel mulch, drip on contour |
| Moderate slope, soil moves in storms | Keyed boulders in staggered rows, erosion netting, dense planting |
| Steep bank you can't stand on comfortably | Terrace with low walls, or plant tough groundcovers and shrubs through netting |
| Slope receiving roof or street runoff | Add a dry creek bed or swale to carry water across and off the slope |
Plant like a root system, not a decorator
Plants are the permanent erosion control; everything else buys time until they knit together.
- Deep-rooted anchor shrubs every few feet: three-leaf sumac, rabbitbrush, Apache plume and big sagebrush on the Front Range and in the Great Basin. Panchito manzanita is a low, spreading evergreen for partial-sun banks. More in drought-tolerant shrubs.
- Bunchgrasses between them. Little bluestem and blue grama root deep and hold soil through winter (grass picks).
- Spreading groundcovers to close the gaps: creeping veronica, hardy ice plant and sulphur buckwheat. The groundcover roster has more.
- Plant densely. Slopes are the one place to overplant on purpose. Aim for full coverage in two seasons, not five.
- Match plants to the microclimates. The dry, sun-blasted top gets the toughest natives; the moister toe of the slope can take thirstier perennials.
Water without runoff
Spray irrigation on a slope is a runoff machine. Use drip, or convert the old spray zone, with these slope-specific adjustments:
- Run lines across the slope on the contour, with emitters on the uphill side of each plant so water soaks down into the roots.
- Use pressure-compensating emitters. CSU Extension explains that they deliver the same flow over a wide pressure range, while ordinary emitters put out more at higher pressure, which on a slope means the bottom of the run gets more water. CSU also notes that each 10 feet of rise above the water source needs about 5 psi more operating pressure.
- Cycle and soak. Several short runs with breaks between them let water soak in instead of running off. EPA WaterSense recommends the cycle-and-soak method, and many controllers have it built in.
Hold the surface while plants establish
- Gravel mulch beats wood on grades. Bark floats and migrates downhill in the first storm (the mulch matchup). Use angular crushed rock, which locks together, rather than rounded pea gravel, which rolls. CSU recommends most mulches at 3 to 4 inches deep.
- Jute or coir netting pinned over bare soil between new plants holds everything through the first year, then breaks down as roots take over. On bigger slopes, straw wattles laid on the contour work the same way; CSU's erosion fact sheet describes placing them perpendicular to the slope so runoff has no straight path down.
- Skip plastic and woven weed fabric. Water races along the top of it and takes the mulch with it, and CSU doesn't recommend either under landscape mulch (weeds in gravel covers why).
- Patrol the first year. Refill basins after storms and repair washouts quickly. First-year care is when a slope is won or lost.
The payoff
By year three the roots have knitted, the boulders have settled in, and the hill you used to mow sideways has become a terraced, blooming rock garden that holds the rain it used to shed. For layout ideas, see backyard xeriscape ideas and the front yard roundup. Foothill cities have plenty of sloped lots; our Salt Lake City and St. George guides cover regional plant picks.
From our installs: on Front Range hillsides, the slopes that fail are usually the ones mulched with wood and watered with the old spray heads. The first hard thunderstorm moves the bark to the sidewalk and cuts rills between the plants. We switch those to drip on contour, key in boulders on the steepest sections, use angular gravel instead of pea gravel, and plant groundcovers tight between shrubs. Clay slopes absorb water slowly, so we water them in two or three short cycles rather than one long one.
Frequently asked questions
What is the best ground cover for a slope with no grass?
Spreading, deep-rooted groundcovers such as creeping veronica, hardy ice plant and sulphur buckwheat, combined with shrubs and bunchgrasses for deeper roots. Use erosion netting and angular gravel mulch to hold the surface until they fill in.
How do you stop erosion on a slope?
Slow the water and hold the soil. Terrace or set boulders across the slope, plant densely with deep-rooted plants, cover bare soil with netting or angular gravel, route concentrated runoff into a channel, and water with drip in short cycles instead of spray.
Should you use landscape fabric on a slope?
Generally no. Water and mulch slide across the fabric's surface, weeds root into it over time, and CSU Extension doesn't recommend woven fabric under landscape mulch. Biodegradable jute or coir netting holds soil during establishment and then breaks down.
How do you water plants on a slope?
Use drip lines laid across the slope with emitters on the uphill side of each plant, pressure-compensating emitters so the bottom doesn't get more water than the top, and several short cycles with soak time between them.
