Turn a Retaining Wall into a Flower Waterfall with Aubrieta

Many keen gardeners plan their borders, lawns and patios down to the smallest detail, yet the retaining wall is often left as a mere supporting player: bare, grey and functional. That overlooked spot offers enormous potential. Choose the right plant and it can become one of the most striking features in the whole garden – without the need for constant watering or feeding.

Why a retaining wall is perfect for these flowering cushions

Retaining walls are generally considered challenging places to grow plants: there is little soil, plenty of heat and wind, and rainwater drains away immediately. Many garden plants fail in these conditions. Alpine cushion perennials, however, are ideally suited to them. Originating in rocky regions, they grow in cracks and on sparse slopes – precisely the conditions found on a wall.

Aubrieta is especially well suited to the job. Also known as rock cress or purple rock cress, its botanical name is Aubrieta deltoidea. It stays low, forms dense cushions and spreads widely sideways. Then, in spring, it puts on a real display: from around mid-April into early summer, hundreds of small violet flowers appear, sometimes with pink or purple tones.

“Within just a few weeks, the wall no longer looks like a foreign object in the garden, but like a natural rocky slope drenched in a lilac waterfall of flowers.”

The plant thrives in sunny, warm, free-draining conditions – exactly where other plants may scorch or dry out. Its stems creep across the stones, locate crevices, take root and then spill gently over the front of the wall in soft cascades. The stones remain secure, but their hard appearance is visually softened.

The best position for Aubrieta: start the flower waterfall at the top of the wall

To create the characteristic “waterfall effect”, do not plant at the base of the wall. Place the plants along its upper edge instead. Their shoots can then trail downwards, gradually covering the surface.

• Position: full sun is essential; a south- or west-facing aspect is ideal
• Soil: poor to average soil is suitable, but it must drain freely
• Wall height: from roughly 60 cm upwards, the cascading effect is especially impressive
• Companion plants: other rock-garden plants, such as houseleeks or sedums, are a good visual and practical match

Ideally, the top of the wall has a narrow strip of soil or gaps between the stones. This is where the Aubrieta’s “starting bed” is created. Heavy, unaltered garden soil is unsuitable because it retains too much water and compacts easily. A loose, stony growing medium is the better option.

How to plant Aubrieta in a retaining wall

Using small young plants in pots, rather than seed, is the quickest approach. They can be placed precisely into gaps and planting pockets without needing to rebuild much of the wall.

Mix the growing medium and prepare planting pockets

First, make small pockets between the stones or behind the top row of stones. Fill them with a loose mixture of:

• around 50% ordinary garden soil
• 20–30% well-rotted compost
• 20–30% grit or coarse gravel

This blend allows surplus water to drain away quickly, preventing the roots from sitting in wet soil. Aubrieta prefers conditions that are slightly dry rather than overly damp.

The right time to plant

There are two suitable planting periods:

• Spring: after the last hard frosts, once the soil has dried out
• Autumn: during a mild spell, so the roots still have time to establish

Carefully remove the young plant from its pot, loosen the rootball slightly and set it into the prepared pocket. Position it with a slight outward slope so rainwater does not collect around the plant. Water thoroughly once afterwards, allowing the soil to settle around the roots. From then on, watering less often is preferable to watering constantly.

Care: little effort, plenty of impact

Once it has established well, Aubrieta is among the most rewarding garden plants. It does not need regular attention with a watering can, nor does it require heavy feeding.

Watering, feeding and pruning to keep the flowering carpet dense

• Watering: only during extended dry spells in the first year; established plants cope well with drought
• Feeding: a light application of compost in spring is entirely sufficient
• Pruning: cut the cushions back by about half after the main flowering period

Cutting back after flowering has two benefits: the cushions stay compact rather than becoming woody and sparse, while fresh young shoots form and flower abundantly again the following year. If pruning is skipped, bare patches often develop in the centre of the cushions after a few years.

“A single cut with the shears in early summer often determines whether the wall continues to resemble a dense carpet or gradually develops gaps.”

There is another benefit: the lilac flowers attract insects. Bees and butterflies use the cushions as a food source. Deer and rabbits, by contrast, show little interest in the plant – a useful point for gardeners in rural areas.

Aubrieta varieties particularly suited to retaining walls

Garden centres offer numerous cultivated forms, with slight differences in flower colour and growth habit. For walls, the best choices are chiefly robust types that form strong, dense cushions.

• Purple rock cress varieties: classic violet-blue flowers and compact growth
• Pink and purple forms: add greater depth of colour to the wall
• Double-flowered varieties: look refined, though they often flower for a slightly shorter period
• Repeat-flowering varieties: can produce a further flush in late summer under favourable conditions

For greening a larger wall, plant several varieties alongside one another. This creates waves of colour without making the overall effect look busy. A spacing of roughly 25 to 30 cm between young plants is sufficient, as the cushions quickly grow together.

Ideal companion plants for a lively wall mosaic

A retaining wall looks even more impressive when Aubrieta does not grow alone, but is combined with other rock-garden plants. Suitable choices include:

• houseleeks (Sempervivum) for their graphic rosettes
• different sedum species with yellow, white or red flowers
• thyme for fragrance and additional flowers
• early-flowering bulbs, such as small daffodils, along the top edge

The result is an ever-changing display throughout the year: bulbs begin in early spring, followed by Aubrieta’s lilac curtain of flowers. Sedums and thyme provide accents in summer, while houseleeks maintain their structural role all year round.

Risks, limitations and a few honest points

This method does have its limits. Anyone with a permanently wet, shaded north-facing wall is unlikely to get much pleasure from this plant, as it needs sunshine. Completely smooth concrete walls without joints also offer neither anchorage nor soil; planting blocks or wall baskets are often the better choice in those cases.

The wall should also be structurally sound before it is planted up. Plants may hide cracks visually, but they cannot replace proper structural stability. In addition, using very nutrient-rich soil and feeding heavily can result in lush but short-lived cushions that become matted more quickly.

Why this project is especially worthwhile for new gardeners

Beginners in particular often underestimate difficult sites such as retaining walls and mentally dismiss them as “impossible to plant”. Yet this is exactly where a simple, inexpensive perennial can create a surprisingly effective result – without complicated care instructions or costly specialist materials.

With a few pots of Aubrieta, a wheelbarrow of soil-and-grit mix and half a day’s work, you can create a project that becomes more impressive year after year. The formerly dreary retaining wall almost disappears behind a lilac slope of flowers, suddenly looking like the deliberately designed centrepiece of a thoughtfully planned garden.