Earthquakes are not the only cause of landslides: heavy rainfalls wash away precious topsoil on unprotected slopes, leaving gullies and slumps. But banks covered with grass, blackberry, horsetail or ivy are not prone to erosion, nor are forested ravines that are shaped by spectacular ranks of sword ferns beneath the trees. How can we clear the invasive blackberries and ivy while holding up our banks?
Start with good drainage above the vulnerable area. Make hard landscape surfaces porous, to reduce the amount of run-off, and direct any run-off away from the bank — but never into the neighbour’s yard!
One solution is to terrace the bank, providing relatively flat areas separated by retaining walls. Another option for small areas is to carpet the slope with cobble-sized rocks, carefully placed for stability, adding small plants in some of the small spaces between the cobbles.
Plant roots hold the soil together, so, having cleared the blackberries or cut the trees, new plants must be established as soon as possible. Grass is often hydro-seeded in an oddly green mix containing both seeds and mulch. Or peg an erosion control blanket impregnated with grass seed over the slope. Once a grassy bank is established it is easier to add larger plants, whose deeper roots help to avoid surface slumping.
If grass or retaining walls are impractical or unwanted, place several low horizontal barriers across the slope to hold back pockets of soil for the new plants. These barriers may be logs, lumber or landscape ties, held in place with rebar or wooden stakes, or wattle fences. Willow stakes will take root.
Choose a mix of appropriate plants to repopulate the slope — many native species work well. Use ground covers as well as larger, deeper-rooted material. Do not plant invasives such as ivy, lamium or periwinkle.
A permit from the SCRD may be required before removing trees growing on steep banks. Think twice before denuding slopes of their natural vegetation, because you will then be responsible for the job of maintaining the slope.
— Sheila Watkins, Coast Resident Master Gardener