Good 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, 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 do you start?

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.

First you need to think about 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.

If the area is large and your slope is at least 30%, creating terraces would be good option for making more level planting, recreation, and seating areas. 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 collection of run-off sediment to collect around the trunk. Terraces should be slightly sloped perpendicularly to the hillside to allow for run-off. In areas of heavy rains, pipes with drainage holes can be laid along the terraces in gravel runs then stabilized with rock edging. I prefer soaker hoses and drip irrigation which allow easy adjustments to the water delivery for each plant. Remember that deeper,infrequent watering is the best approach.

Planting well-rooted groundcover is the easiest solution. One of the best evergreen choices for a sunny area is myoporum parvifolium, a small leathery-leafed member of the myrtle family, 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"-4" with a 6 ft. spread. This plant is also fire retardant and deer resistant, especially the "Putah Creek" variety. It does attract bee activity in April-June. Other varieties of Myoporum can be hosts to blow flies, so choose carefully. Myoporum typically lasts for 5-6 years.

For areas in shade, one of the best evergreen groundcovers is Pachysandra terminalis commonly referred to as "green carpet." It can be slow to start but will be vigorously growing by the 3rd year. It grows to 6"- 10" high and spreads by rhizomes. It is good for erosion control and will grow under trees, including pines. It has insignificant white flowers in Spring, and is not bee attracting.

Here in California I like to use our native flora, so I personally recommend Fragaria chiloensis.This beautifully fragrant strawberry is a great groundcover well-suited for both sun and shade. In hot inland areas, however, it needs protection from the hot summer rays. It produces lovely white flowers for our butterflies and fruits for our birds. In other zones, Fragaria virginiana might be a better substitute,

It's always best to take cues from nature, so I think the best approach to a slope or hillside is a combinaton of trees, shrubs, and groundcovers. Not only are they more visually appealling, they will attract more birds and wildlife and break the rainfall which reduces erosion.

When clearing your area for planting, it's best to leave a bit of organic debris. Sticks, stones, and bark help fortify the soil against run-off. Shredded bark is a good mulch to add. I prefer shredded redwood which has a more fur-like quality. It stays matted and is less apt to be disturbed by winds and blowers. Create shelf-like basins around trees and shrubs that are planted into the slope and use varying sizes of rocks for stability and attractiveness. 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 groundcover. Jute netting can be used to anchor the hillside until the plants have grown in. It will gradually disentigrate. Sometimes birds or squirrels will swipe it for nesting!

Accessibility is often a problem with sloped areas, so I recommend choosing drought tolerant varieties and being careful to not overfertilize. You don't want to encourage weeds. Newly planted trees and shrubs, even those for xeriscape, will still need regular deep water until established. The addition of a michorrizae-based organic fertilizer at the time of planting wil help the plant grow more vigorously since it helps the uptake of nutrients.

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!

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Suggestions for suitable erosion-control and wildlife:

There are so many choices including cacti and succulents. The considerations would be low maintainence and deeper rooting unless terracing allows easy access for pruning and clean-up.

Australian varieties:

Grevellia- many varieties

Phormium- New Zealand Flax

Westringia- Australian lavendar

Callistemon "Little John"- dwarf bottlebrush

California

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 groundcover. They have beautiful sculptural shapes,red bark, and white Spring flowers which provide food for hummingbirds.

Salvia- many varieties

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