While slope gardening does have its challenges, it provides the home gardener with the opportunity to create something unique in the garden.
Retaining walls and terracing provide a solution for steeper slopes. Before embarking on any project on a slope, especially steep slopes, enlist the services of a professional landscaper.
The site needs for be assessed for gradient, soil structure and water run-off. Any structure that needs to be constructed above the slope or retaining wall must also be taken into
account. Incorrect project execution may result in soil erosion or sliding and injury or damage to people or property.
Tackling a terrace
“Terraces can be cut into an embankment and stabilised with a number of materials, creating a variety of level areas and interest within the garden,” explained Colin de Wet of Peninsula Landscaping in Cape Town.
Terracing is a good choice for a steep slope. Walls may be constructed from brick, railway sleepers, stone, concrete or gabions. Traditionally, grass was planted between the lifts but gardeners are getting creative with their plantings. Plantings may be ornamental or spaces can be used for food gardening.
Raising a retaining wall
“Property owners on steep slopes are able to extend their usable land by erecting a retaining wall and backfilling with imported fill material,” said de Wet. “Engineers’ specifications need to be followed and external loading factors such as building foundations and traffic use needs consideration.”
Interlocking concrete blocks, wooden poles or gabions, wire cages filled with stone or rocks, are popular material choices for retaining walls.
De Wet said that currently, retaining walls above one metre should be signed off by an engineer and fill material stacked on a property must not exceed two metres in height. A structural engineer should always be consulted if the slope is very steep. Plans for retaining walls may need to be drawn up and approved at your municipality’s building office before any work commences.
Terracing retaining walls
“Retaining walls, using interlocking concrete blocks or gabions, can be also terraced by intermittently stepping back the concrete interlocking blocks or gabions,” explained de Wet. “This enables one to plant on each terraced l
evel. All walls need to have structurally sound foundations and adequate drainage installed to ensure there is no pressure build up against the wall.”
Depending on the gradient and according to an engineer’s specification, the lower levels of concrete blocks are filled with concrete to secure the foundations. Blocks higher up in the wall can be filled with a growing medium and planted. “The pockets in these blocks are small and can dry out quickly, so it is advisable to plant in your rainfall season to encourage establishment of plants,” advised de Wet.
Plants suitable for retaining walls: succulents, trailing arctotis (Arctotis stoechadifolia), portulaca spp., creeping fig (Ficus pumila), ivy-leaf geranium (Pelargonium peltatum), Boston ivy (Parthenocissus tricuspidata), and Osteospermum spp.
For more information, contact Peninsula Landscaping on +27 21 715 7046/7 or visit their website: www.penland.co.za. For engineering advice for retaining walls and bank stabilisation, contact Brennan Rutherford on 086 117 2774.