Slope planting adds bright sparks
Johannesburg - The ridge running through Joburg, together with isolated koppies hardly justify a celebration of World Mountain Day on Wednesday December 11.
This notwithstanding, there are a number of local gardeners who have to cope with the challenge of gardening on the slopes of hills, koppies and ridges.
One of the keys to successful slope gardening is the opportunity to grow plants with similar needs of well-drained soil.
The fynbos of the Western Cape is an example of plants that thrive on mountain slopes. It’s not surprising therefore that proteas thrive in these conditions on Northcliff Hill. Proteas not only attract nectar-loving birds, but also vary in height from low-growing species, such as the dainty Protea scolymocephala with yellowish-green blooms, to the king protea, Protea cynaroides that grows to 2m, Protea neriifolia and the sugarbush P. repens.
Trees that thrive on slopes include as the wild olive (Olea europaea subsp. africana) and shrubs such as the lion’s ear (Leonotis leonurus) with tall upright stems of velvety flowers arranged in tiers attract sunbirds. Orange is the most common colour in leonotis, but there are also cream and apricot forms.
The confetti bush, coleonema, with masses of tiny pink flowers and needle-like leaves that when crushed release an aromatic fragrance, is a good companion plant for proteas. The foliage of Coleonema “Sunset Gold” makes a pleasing contrast among plants with green foliage. Different textures are found in bushes with aromatic foliage, such as Eriocephalus africanus (wild rosemary) with tiny white flowers.
Dealing with slopes
What will grow on slopes depends on climate and aspect. Slopes that face east and south-east are usually wetter and cooler than those facing west. In cold winter gardens, frost collects in hollows and at the foot of hillsides and sloping ground.
Slopes cleared of vegetation create problems with erosion, and soil on slopes is often poor because the topsoil has washed away. This makes them suitable for plants that do not need rich soil but need excellent drainage. Small shrubs can be planted closely as groundcovers, such as pink Anisodontea scabrosa, the yellow daisy-like flowers of euryops and the honey-scented bells of freylinia.
Salvia africana-caerulea, the blue sage, with greyish-green aromatic foliage, Salvia africana-lutea, with rusty-brown flowers, and summer flowering Salvia chamelaeagnea with blue, mauve, pink or white flowers also suit these conditions.
Even a slight slope is perfect for agapanthus, arctotis, felicia, gazania, mesembryanthemum and dimorphotheca. Succulents such as Cotyledon orbiculata with orange-red tubular bell-shaped flowers and succulent large grey-green leaves, and cistus, lavender and rosemary that grow on the cliffs of the Mediterranean are also suitable.
Introduce different textures with grasses and grass-like plants to add softness and movement, and clumps of dietes and watsonias with sword-like foliage for vertical interest. Bulbs should be planted randomly to create a more natural effect.
Terracing a hillside is an alternative steep grade solution that creates a series of multi-level areas and an opportunity to garden on the flat ground of each terrace.
Hillside gardens with steps and meandering paths cut into the hillside can be both dramatic and exciting. If the steps and paths follow the contour of the land, this will ensure slower water runoff and allow easier access for maintenance, planting, weeding and watering. Terraces could feature a sitting out area or a formal pool, flower borders or productive vegetable gardens if the soil is enriched with compost.
Terrace walls can be built of wooden rail sleepers, bricks, rocks or concrete. It is recommended that a professional landscaper build these walls as they will need reinforcing, and weep holes incorporated for rainwater to drain away and prevent walls collapsing, because of the weight of the soil they hold back.
Rock gardens and water features
Natural slopes suit rock gardens and water features. Use weathered rocks with two-thirds of each rock buried into the slope and tilted slightly backwards to allow water to seep into the soil rather than run off.
Water trickling over boulders is a most desirable feature in a garden when it looks natural and flows downwards. A multi-level cascade or waterfall could drop into a pool at the lowest level of a hillside garden. Where an electrical pump has to be installed to re-circulate the water, a professional contractor should be employed.
Mowing and weeding on slopes is not easy and an alternative that will also help prevent erosion is to cover the soil with non-invasive groundcovers. Try trailing arctotis, gazania, osteospermum, prostrate rosemary and ivy geranium (Pelargonium peltatum).
Groundcovers do not need to be low-growing. Agapanthus have succulent type roots that bind the soil, and day lilies planted closely together will help retain soil. Low-growing, spreading plants can be threaded through taller plantings to carpet the ground and reduce maintenance. Compact bougainvilleas are suitable for draping over retaining walls, or as groundcovers on sloping ground. Trachelospermum jasminoides (star jasmine) with scented white flowers in summer is usually grown as an evergreen climber, but is just as successful when grown on banks. Transforming a slope or hillside into an interesting and beautiful garden can be very rewarding.
GENERAL GARDENING TIPS
* Depressions in the garden where water collects are great spots for planting moisture-loving plants, such as white arums, astilbes, hostas and Louisiana irises.
* Welcome your visitors with pots of brightly coloured flowers. Pots can be of different sizes and shapes, but group them together for greater impact. If the entrance is sunny, choose marigold, salvia, nicotiana, petunia or vinca, with trailing lobelia and alyssum to soften the edges. The Madeira series of marguerite daisies (argyranthemums) are compact growing and very floriferous, making them ideal for containers.
* Dress up bare spots in a shade garden with flowering pots of shade-loving annuals, perennials or shrubs. Plants suitable for shady entrances include hydrangeas, fuchsias, bedding begonia and New Guinea impatiens. Torenias are compact with dainty flowers of blue, purple or pink with yellow throats, and are suitable for edgings, beds, pots, hanging baskets and window boxes.
* Summer rains wash away nutrients so fertilise lawns with Blade Runner, shrubs and flowers with Bounceback, and feed container plants with Multifeed Classic, a water-soluble fertiliser. Let the leaf blades grow up to 30 percent longer than usual to protect the roots from very hot sunshine. - Saturday Star