Wednesday 2 August 2017

Planting for Slopes and Banks

Apologies for the long break in posts.

Early this year I started an on-line certificate course "Design for Sustainability" being run by Gaia Education. This will keep me occupied until September next year. (More about this in a later post.) Although it is a part time course I found myself becoming totally absorbed in it and am spending far too long reading and researching around the topics covered. Well that, plus the minor issue of getting my brain back into gear, as it is over 50 years since I have undertaken any formal academic study and research!!

So back to the problem of stabilising slopes using drought tolerant plantings.

How slopes and banks are planted up is important because there is always potential for erosion. Each and every raindrop that falls on the bare soil dislodges soil particles. As the run off runs down the hillside more and more soil particles are gathered up. Scaling this up by the duration of a rainstorm shows how easy it is to lose ground due to unchecked erosion.

Plants are the natural preservers of soil. By covering the ground in foliage rain drops are prevented from directly falling onto the soil particles. The plants diffuse the energy of the raindrops resulting in them filtering down to the soil surface more gently. In addition the plant roots help to bind the soil underground. It therefore follows that those species that have a large proportion of fine roots that spread over a large area prove the best choices for slope stabilisation.

A reminder of the sort of challenge the site presents in terms of stabilisation.

Another important slope to be stabilised.

From a lot of background reading and internet research the following  is a detailed list of possible plantings.


Drought tolerant trees suitable for planting in terraced areas and in any berms created when on contour swales are used include:

Tree of Heaven - grows rapidly, does well under adverse conditions
Hackberry (Celtis occidentalise) - deep rooted, bears small fruits
Staghorn Sumac (Rhus typhina "Laciniata")


Drought tolerant, deep rooted shrubs suitable for planting at strategic points to improve the soil's stability include:

Rock rose (Helianthemum)
Manzanita (Arctostaphylos)

Herbaceous and woody plant ground cover

Chokeberry (Aronia melanocarpa) - for dry slopes liked by pollinators
Cinquefoil (Potentilla fruticose) - becomes twiggy needs pruning
Spring cinquefoil (Potentilla tabernaemontanii)
Fragrant Sumac (Rhus aromatic) - good for sunny dry slopes.
Juniper (Juniperus chinensis, J.sargentii, J. procumbens)
Stink bush sumac (Rhus trilobite) - tolerates dry sites
Rugosa rose (Rosa rugosa) - prefers well drained sites
Sweet fern (Comptonia pergrina) - grows on poor sites, salt tolerant
Barren strawberry (Waldsteinia fragarioides)
Wild/Sand strawberry (Fragaria chiloensis)
Sky lupine (Lupinus nanus) - sow seed in fall on bare slopes and banks
Big root geranium (Geranium macorrhizum) - attracts bees
Carnation sedge ( Corex flacca) - aggressive rhizomes
Three-toothed cinquefoil (Sibbaldiopsis tridentate)
Trefoil, Birdsfoot (Lotus corniculatus) - heat resistant, salt tolerant
Rockrose (Cistus spp.)
Snow in summer (Cerastium tomentosum)
Winecups (Cullirhoe involucrata)
Creeping phlox
Moss phlox (Phlox subulata)
Ice plant (Delosperma)
Evening primrose
Common thyme (Thymus vulgaris)
Creeping thyme (Thymus serphyllam)
Creeping sage (Salvia sonomensis)
Black sage (Salvia mellifera tera seca)
Purple sage (Salvia leucophylia)
Beach sunflower (Helianthus debilis)
Lantana montevidensis
Manzanita (Arctostaphylos)
Wild lilac (Ceanothus spp.)
Sage leaf rock rose (Cistus salviifolius)

Fast growing ground cover

Cotoneaster (Cotoneaster spp.)
Mexican daisy (Erigeron karvinskianus)
Gout weed (Aegopodium podagraria) - overly enthusiastic, greedy
Asian Jasmine (Trachelospermum asiatico) - aggressive vining plant
Ajuga restons - pushy plant keep out of small gardens
Thymus serphyllum - not as fast as above, soon forms self seeding mat
Creeping rosemary (Rosemarinus officinalis "postratus")
Trailing rosemary ("Irene")
Sedum spurium
Salvia (Bee's Bliss/Gracias) - can cover a slope very quickly.
Go-kum (Carpobrotus acinaciformis) - good bank cover but can become invasive if not controlled.

Erosion controlling ground covers,shrubs and plants

Mimosa (Mimosa strigillosa) - deep roots good for erosion control
Californian fuchsia (Zauschnerin californica) - excellent for steep slopes
Creeping cotoneaster (Cotoneaster adpressus)
Aaron's Beard/Creeping St John's wort (Hypericum calycinum)
Coyote brush (Baccharis pillars) - good for slope stabilisation
Carnation (Dianthus) - does good job locking down soil on slopes
Creeping juniper (Junipers horizontalis)
Acacia redolens - highly drought resistant creeping shrub
Daylillies - massive root systems makes ideal for banks
Manzanita (Arctostaphylos)


Sheep fescue (Festuca ovina "Glaucu")
Deergrass (Muhlenbergia rigens)
Side oats grama (Bouleloua curtipendula)
Blue grama (Bouleloua gracilis) - will form sods, grows on steep banks
Sand dropseed (Sporobolus cryptandrus) - pioneer, deep-rooted

A couple of mixed plantings proven to work well in drought conditions

Mix 1

Salvia Bee's Bliss or Salvia Gracias - mixed with some
Penstemons - for colour and some
Manzanitas and Ceanothus - for stabilisation

make a proven winner.

Mix 2

Manzanita + Harmony Manzanita with
Ceanothus Joyce Coulter and
Ceanothus Mill's Glory

make a great bank cover.