If an upcoming project is to build a rock wall, consider making it a real work of art with the addition of colourful plantings.
Although free-standing stone or rock walls are a pleasure to behold, without the addition of plants to soften their hard edges, they can be rather stark and featureless.
A combination of plants spilling over edges or tumbling from crevices will break the monotony of stone by creating a palette of colours that changes with the seasons. Do allow some of the beauty of the rock face to show through by keeping a portion of the surface area free of plants. This allows the beauty of the stone to be enhanced, rather than obscured.
Once the plants are established, a rock-wall garden requires little maintenance other than trimming flowers past their prime, or keeping overly exuberant plants contained.
Following are 10 of my favourite plants for dressing up a rock or stone wall.
1. Aurinia saxatilis (or Alyssum saxatile) provides a thick, glorious mat of bright-yellow flowers. Blooms in late spring and early summer. After the plant has finished blooming, trim back to keep the plant compact. Prefers well-drained soil, but will tolerate most soil conditions. Plant 20 to 30 centimetres apart, in full or part sun. Grows 1.8 to three metres tall. When mature will provide great cascades of colour. Take cuttings in spring.
2. Aubrieta – If there’s a stone wall in your neighbourhood, you’ll probably find one of the beautiful Aubrieta hybrids spilling over the edge. A very popular plant for walls and rockeries, colours range from pale lavender to pink to violet-blue. Free-flowering plants form large mats of blossoms that practically smother the plants from spring to early summer. Will cover a large area. Prefers a well-drained, alkaline soil. Plant in full sun. Height ranges from eight to 15 centimetres. After flowering, cut all the old flowerheads and any straggly shoots. Easily propagated from cuttings, or grown from seed. Trim back the shoots after flowering to keep the plant compact. Hardy. Plants can be divided in spring or autumn.
3. Arabis (rock cress) is very easy to grow. Plants will cloak a large area with pink or white flowers. Provide a well-drained soil in full sun or partial shade. Propagate in autumn, or take cuttings in summer. Looks great planted with Aubrieta as both flower at similar times and make an excellent showing together. Plants are low-growing, and form a thick mat. Has a somewhat sprawling habit and may become quite invasive. Very fine flowers in white, pale pink or lilac that grow to a height of 15 to 20 centimetres. Blooms spring to early summer. Dark-green foliage. Plant in sun or partial shade. Easy to grow and tolerant of most soil conditions. Use for draping over rock walls, in borders, or as ground cover.
4. Iberis sempervirens is a perennial candytuft that is outstanding in a sunny place. Grows 15 to 30 centimetres in height. This plant spreads quickly and needs to be contained. Once it has a firm root-hold, nothing will stop it. Flowers in spring and early summer with clusters of pure white flowers. The leaves are evergreen. Plant in sun or part shade. Tolerates most soil conditions. Trim lightly after flowering. Severe pruning may prevent the next season’s blooms.
5. Dianthus deltoides makes an excellent crevice plant. Low-growing with semi-evergreen foliage that bears single blossoms in pink, red and pure white. Like other Dianthus, has a clove-like fragrance. Flowers freely June through September. Height is 15 to 23 centimetres. Leaves are evergreen. Provide a well-drained, alkaline soil in full sun. Take cuttings in summer. Use for edging or rock walls.
6. Dwarf genista (broom) is excellent for cascading over a stone wall – the pendulous branches of this low-growing shrub become covered with a mass of deep yellow flowers. Easy to grow and dependable, it provides a stunning visual effect. Ensure it a sunny position.
7. Cerastium tomentosum (snow-in-summer or snow-on-the-mountain) is a great plant for spilling from crevices in walls. Easy to grow. Forms a large mat of flowers in loose clusters, and may be too invasive for a small area. This plant provides great drifts of white flowers that cascade over walls for a lovely effect. Has silvery-grey foliage. Another sun-worshipper. Blooms spring to early summer. Tolerant of most soils.
8. Daphne blagayana is a beautiful evergreen species with shiny, dark-green foliage. It blooms profusely with intensely fragrant pink flowers from spring to early summer. This is a somewhat cantankerous plant that requires well-drained soil that doesn’t dry out and prefers to have cool roots. Thrives in full sun or partial shade. Propagate by seed, cuttings or layering. Try the ground-covering shrub, rose daphne (D. cneorum).
9. Gentiana acaulis (trumpet gentian) bears graceful, arching stems with intense-blue trumpet-like flowers, over five centimetres long. Blooms in late spring and early summer. Can be somewhat fickle to grow. Provide full sun or partial shade. Few flowers can match the brilliant blue of the gentians. G. acaulis prefers an acidic, moisture-retentive soil.
G. verna (alpine gentian) flowers later in the season. It carries smaller flowers or trumpets 2.5 centimetres long, variable in colour from bright to pale sky blue, and sometimes white. Plant in well-drained, alkaline soil.
G. septemfida is somewhat easier to grow, and has purple-blue flowers that bloom mid to late summer. For autumn colour, the intense blue G. sino-ornata blooms in early to mid autumn.
Divide plants in early spring to take cuttings in mid or late spring. These plants can also be grown successfully from seed.
10. Armeria maritima (thrift or sea pink) forms a mat of spiky, grass-like tufts with masses of white, deep-rose or crimson flowers held erect on stiff stems. The flowers form globular balls that grow to a height of 15 to 20 centimetres and look great massed on rock outcroppings. Blooms in late spring and early summer. Provide well-drained soil in full sun. Propagate by seed or cuttings taken in spring or fall.
Choose a few of these perennial beauties to dress your rock wall, and add a vertical dimension to your gardening. You’ll know you’ve hit the right combination when passersby stop to take a second look, then make a mad dash for their camera!
Freelancer Jutta Boras divides her time between writing about flowers and growing them in her garden on the Sechelt peninsula.