Best Plants and Erosion Controls for Slopes and Hillsides
One of the greatest challenges to both the home gardener and the professional landscaper is a steep slope. Wind and water wreak havoc on the topsoil, uniform water penetration is poor with additional run-off, and the thought of clearing weeds makes us want to go back to bed and pull the covers over our heads! Where does one start?
Options for Hillside Landscaping
There are a few different options such as building retaining walls, terracing with horizontal paths, laying down erosion-control grids, constructing shelf-like basins around trees and shrubs, and selecting deep-rooted groundcovers. They can all work effectively, but each has its own considerations. Of these options, planting well-rooted groundcover is the easiest solution.
What to Consider Before You Start?
First, consider the size of the area and the pitch of the slope. You'll also want to take note of any existing trees and shrubs and the boundaries of neighboring properties. These will all figure in to your final decision.
Terraces: If the area is large and your slope is at least 30%, creating terraces would be a good plan for making more level planting, recreation, and seating areas. Terraces should be slightly sloped perpendicularly to the hillside to allow for run-off.
Retaining Wall: Another option for a steeply sloped area is a retaining wall, but these work best in a smaller area where the run isn't too long. A wall can be both costly and subject to damage due to shifting earth. If you do put in a retaining wall, it is important to think about how it will affect any existing trees. You'll have to be careful not to damage roots and to not allow the run-off sediment to collect around the trunks.
Pipes: In areas with heavy rain or poor soil, pipes with drainage holes can be laid along the terraces in gravel runs then stabilized with rock edging. Soaker hoses and drip irrigation allow easy adjustments to the water delivery for each plant. Remember that deeper, infrequent watering is the best approach.
Best Ground Covers for Sun
Four great evergreen choices for a sunny area are Myoporum parvifolium, Rosmarinus officinalis "prostratus," Lippia repens, and Baccharis pilularis. All of these prefer well-draining soils and are tolerant of drier conditions once established.
1. Myoporum parvifolium
Also known as creeping boobialla or dwarf native myrtle, this ground cover is a small, leathery-leafed member of the myrtle family.
- It blooms in spring with pink or white flowers.
- It is deeply rooted and has dense overlapping, finger-like stems, which block out weed growth.
- It grows to 3 to 4 in. with a 6 ft. spread, and typically lasts for 5-6 years.
- This Australian native is also fire retardant and deer resistant, especially the "Putah Creek" variety.
- It does attract bee activity in April-June.
2. Rosmarinus officinalis "prostratus"
Also known as creeping rosemary, this variety is a common rosemary in a low-growing and spreading form.
- It is a hardy Mediterranean native that is well-suited to sunny and water-wise gardens.
- It can grow to 1 ft. with a 6-8 ft. spread.
- It is wonderfully fragrant ad can be used for cooking.
- It produces lovely bee-attracting lavender-blue flowers from winter to late spring and is resistant to both insects and deer.
- The "Huntington's Carpet" variety is less woody and works especially well for cascading over retaining walls.
3. Baccharis pilularis
Commonly referred to as dwarf coyote bush, this ground cover is a California native, which grows 1 to 2 ft. high with a 6 to 8 ft. spread.
- It is evergreen and can get along with little water once established.
- It is long-lived, low maintenance, and deer resistant.
- The "Pigeon Point" variety is a good one and looks beautiful combined with flowering accents, like California poppies and salvias.
4. Lippia repens
Also called Phyla nodiflora, this plant is a very low-growing evergreen with a dense matting habit.
- It attracts bees with its pretty clusters of lavender flowers in spring and fall.
- This sun-loving ground cover is a great alternative to myoporum for those desiring fast growth.
- It can get a bit aggressive, so for those wishing for a tamer version, there is the sterile, non-seeding Kurapia.
- Although it is drought-tolerant once established, this will do best with supplemental irrigation in hot areas.
Best Ground Covers for Shade
For areas with more shade, four good choices for evergreen ground covers are Pachysandra terminalis, Fragaria chiloensis, Arctostaphylos "Emerald Carpet," and Satureja douglasii.
1. Pachysandra terminalis
Commonly referred to as "green carpet" or Japanese spurge.
- It can be slow to start but will be vigorously growing by the 3rd year.
- It grows to 6 to 10 in. high and spreads by rhizomes.
- This Asian native is good for erosion control and will grow under trees, including pines.
- It has insignificant white flowers in Spring and is not bee attracting.
2. Fragaria chiloensis
Also known as Beach strawberry, this evergreen ground cover is a California native, well-suited to areas of part-sun to shade and well-drained soil.
- It bears white flowers from spring through summer, produces edible fruit in fall, and has touches of red foliage for year-round interest.
- It is a must for bird gardens and dappled woodlands.
- It stays under 1 ft. with a 12 to 18 ft. spread and needs moderate water.
- A similar alternative is the woodland strawberry (Fragaria californica) whose leaves are brighter green and less leathery.
3. Arctostaphylos "Emerald Carpet"
Another California native from the manzanita family.
- This variety requires more water than the "kinnikinnick" spreading manzanita and is more tolerant of part-shade, but it can handle the inland heat.
- It reaches 1 ft. in height and can spread 6 to 8 ft.
- Small white, bell-shaped flowers appear in winter to spring, followed by red berries.
- The bright green foliage and reddish stems are very attractive. Hummingbirds love the flowers!
4. Satureja douglasii
Also know as yerba buena or Indian mint, this is a fragrant, low-growing evergreen.
- It prefers the shade and moisture of its native habitat, the woodland understory of coastal California.
- It will grow in inland shade with supplemental water.
- It stays under 6 in. with a 3 ft. spread and is non-invasive.
- It is deer resistant and produces white flowers in spring.
Tips for Planting Ground Covers
- Leave some organic debris: When clearing an area for planting, it's best to leave a bit of organic debris. Sticks, stones, and bark help fortify the soil against run-off.
- Use mulch: A good mulch will keep roots cool and suppress weed growth. I prefer coir fiber or shredded redwood, which has a more fur-like quality. It stays matted and is less apt to be disturbed by winds and blowers. Although bark and shredded wood are great choices, the breakdown of carbon can rob the soil of valuable nitrogen. Fertilize accordingly. Create shelf-like basins around trees and shrubs that are planted into the slope and use varying sizes of rocks for stability and attractiveness.
- Create a layered look: Arrange plants for a layered look, using largest in back, then balance the visual layout by randomly placing medium shrubs. Fill in with perennial flowers and clusters of bulbs and ground cover.
- Use jute netting: These nets can be used to anchor the hillside until the plants have grown in. It will gradually disintegrate. Sometimes birds or squirrels will swipe it for nesting!
- Don't over-fertilize: Accessibility is often a problem with sloped areas, so I recommend choosing drought-tolerant varieties and being careful to not to over-fertilize. You don't want to encourage weeds. Newly planted trees and shrubs, even those for xeriscapes, will still need regular deep water until established. The addition of a mycorrhizae-based organic fertilizer at the time of planting will help the plant grow more vigorously since it helps with the uptake of nutrients. California native plants, however, do best without soil additives and fertilizers.
Whatever you choose as your solution, that difficult slope holds the promise of many things. It doesn't have to be a constant source of work. If you tackle it with thought and care, you can eventually sit back, relax and enjoy watching as nature takes over!
Good Water-Wise Plants for Erosion Control and Wildlife
- Grevellia: Many varieties
- Phormium: New Zealand Flax
- Westringia: Coast rosemary
- Callistemon "Little John:" Dwarf bottlebrush
- Quercus chrysolepis: Canyon live oak
- Aesculus californica: California buckeye
- Ceanothus: Many varieties
- Sambucus: Elderberry
- Trichostema lanatum: Wooly blue curls
- Ribes sanquineum: Red-flowering currant
- Baccharis pilularis: Dwarf coyote bush
- Artemesia californica: California sagebrush
- Arctostaphylos: Manzanita. There are many varieties from small trees to shrubs and ground cover. They have beautiful sculptural shapes, red bark, and white spring flowers that provide food for hummingbirds.
- Salvia: Many varieties
- Satureya douglasii: Yerba buena
- Zauschneria: California fuchsia
Miscellaneous (remember to check for your specific areas):
- Salix hookerina: Hookers willow
- Cornus stolonifea: Red-twig dogwood
- Arbutus: Madrone
- Heteromeles arbutifolia: Toyon
- Amelanchier: Serviceberry
- Mahonia: Oregon Grape
- Berberis: Barberry (deciduous shrub)
- Heuchera: Coral Bells
As you can see, there are so many choices! Cacti and succulents are also water-wise and visually diverse; they, however, are not helpful for erosion control on their own because of shallow roots. This is especially true for ice plant, which can slide away like a skin during heavy rains. They do work well when combined with other well-rooted specimens.
The overall considerations should be low-maintenance and deep-rooting, unless terracing allows easy access for pruning and clean-up. Weed cloth also helps to reduce frequent clean-up in these hard-to-work areas.
It's always best to take cues from nature, so I think the best approach to a slope or hillside is a combination of trees, shrubs, and ground covers. Not only can this be more visually appealing, but the variety will attract more birds and wildlife and break the rainfall, which reduces erosion.
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© 2011 Catherine Tally