Rock Wall and Walkway Gardening: Trailing Plants
Image by Carolyn Jones/David Jones
Fill those spaces in your dry-stack rock wall with some hardy creepers, or tuck them between stepping stones to create a whimsical walkway
For me, one of the joys of working in a garden centre was sharing beginning gardeners’ delight at discovering “new” plants—even the most common. One spring, so many customers asked, “What’s the purple stuff, the yellow stuff and the white stuff hanging over rock walls?” that we made a poster with the query and the threesome. As early as March in mild years, purple aubrietia (Aubrieta), yellow alyssum (Aurinia saxatilis) and white candytuft (Iberis sempervirens) burst forth with other spring flowers, announcing another gardening season. Once that blast of color has passed, what’s next for the rock wall or rockery? Here are some suggestions.
The many hybrids and cultivars that fall under the general umbrella of creeping thyme (Thymus) add “foot interest,” as my friend and garden designer Claire Bennett calls it. Planted at the edge of a path, thymes tickle your toes as you go on your way, releasing a Mediterranean aroma. Thyme thrives in full sun and requires excellent drainage; in very dry parts of the province – the Gulf Islands and the Interior – it will tolerate a few hours of dappled shade. My favourites include woolly thyme (usually called T. lanuginosus but correctly called T. pseudolanuginosus), with its hairy leaves that give a greyish cast to the plant, and the lemon-scented thymes, such as T. x citriodorus ‘Bertram Anderson.’ Nomenclature on these little gems is confused, but if you like the look (and aroma!) of a plant, don’t worry about the name – give it a try. Common thyme (Thymus vulgaris) is not suitable for use as a trailer, as it grows upright into a little bush. It is the best one for cooking, though, so worth a spot in the garden. Rock soapwort (Saponaria ocymoides) is a delightful creeper native to the mountains of Europe. It produces pink flowers (a white selection is also available) in early summer, covering a low mat of hairy, bright-green leaves. The flowers are held open flat above a long, narrow calyx – a pleasing arrangement known as “salverform”: platter shaped. Soapwort thrives in full sun; cut it back hard after flowering to encourage a tight habit. Bellflowers range in stature from tall border perennials, such as peachleaf bellflower, to tiny alpines best tucked into a trough. Among those suited to trailing over walls or spilling onto paths is Dalmatian bellflower (Campanula portenschlagiana), which has open, bell-shaped flowers of deep purple that appear from mid- to late summer. Its toothed, heart-shaped leaves are evergreen. It grows to about 15 cm (6 in.) tall and prefers well-drained soil in full sun or part shade. An entirely different look is provided by myrtle spurge (Euphorbia myrsinites). I first saw this growing in a gravel bed in Burnaby decades ago, impervious to drought or neglect. Gardeners east of the Coast Mountains should not grow this evergreen perennial as it has been known to invade wild lands; west of the mountains, where the weather is wetter, it doesn’t misbehave. Creeping jenny (Lysimachia nummularia) is an amazingly adaptable plant. I’ve seen it growing in a pond in North Vancouver and it grew in full sun in a dry spot at VanDusen Botanical Garden. It’s very flat so doesn’t add much textural interest to the garden – best to use it peeking out from low shrubs or perennials, creeping onto a path or trailing from a container or over a wall. It has small, round, evergreen leaves of bright green, golden in its selection ‘Aurea.’ Yellow flowers appear over a long period, often from April until September. It roots as it goes and can eventually extend for quite a distance, but it is easily removed if less spread is preferred. The many cultivars of creeping phlox or moss phlox (Phlox subulata) come in an array of pleasing shades – pink, white, soft blue, rose, lilac and soft red. The fine foliage of fuzzy, vivid green earns it the “moss” common name. Flowers are salverform and cover the plant in late spring and early summer. This eastern North American native thrives in fertile, well-drained soil in full sun on the coast, but in protection from hot afternoon sun in warmer parts of the province. Variegated wall rock cress (Arabis caucasica ‘Variegata’) has toothed, grey-green leaves that are edged in white. The foliage is evergreen, but may look untidy after a wet winter. Fragrant white flowers appear in late spring. The striking feature of woolly lamb’s ears is just that: its wool! Stachys byzantina (formerly S. lanata or S. olympica) spreads gradually and produces fuzzy white stems and large, fuzzy leaves as well. Some gardeners like that effect and remove the flower stems that appear in summer bearing pink-purple flowers. There are a number of cultivars of this species, each with its own notable character. Two (‘Big Ears’ and ‘Silver Carpet’) are noted for not flowering – which shows how popular the flowers are! Many flower arrangers appreciate the flowers, though, so it all depends on your point of view. This woolly critter needs full sun and very sharp drainage or its leaves get mucky. It looks great tucked among rocks. For a shady spot, slip in some charming variegated London pride (Saxifraga ‘Aureopunctata’). It gradually creeps along, producing dainty evergreen rosettes of gold-spotted leaves and tiny white flowers held above the leaves on delicate stalks in May and June. Give it full or part shade, humus-rich, moist, well-drained soil and not too much competition. With all the choices for trailing plants to edge paths or tumble over rock walls or the edges of containers, your garden will be a delight at toe level throughout the season.
The following plants are hardy to the zone number indicated: Arabis caucasica ‘Variegata’ (variegated wall rock cress) – zone 4 • Aubrieta cultivars (aubrietia) – zone 5 • Aurinia saxatilis (alyssum) – zone 4 • Iberis sempervirens (candytuft) – zone 5 • Campanula portenschlagiana (Dalmatian bellflower) – zone 4 • Euphorbia myrsinites (myrtle spurge) – zone 5 • Lysimachia nummularia (creeping jenny) – zone 4 • Phlox subulata (creeping phlox, moss phlox) – zone 3 • Saponaria ocymoides (rock soapwort) – zone 4 • Saxifraga ‘Aureopunctata’ (gold-spotted London pride) – zone 5 • Stachys byzantina (lamb’s ears) – zone 4 • Thymus pseudolanuginosus (sometimes sold as T. lanuginosus) (woolly thyme) – zone 5 • Thymus serpyllum (mother-of-thyme) – zone 4 • Thymus vulgaris (common thyme) – zone 4
With more than 30 years experience in horticulture in B.C. – in wholesale, retail and at VanDusen Botanical Garden for a decade – Carolyn Jones brings a wealth of knowledge and expertise to GardenWise and www.gardenwiseonline.ca