When planting next to a public footpath, it is important to use plants that will not spill out over the sidewalk. An interesting, but tidy planting strip can be created with a repeating pattern of plants with different shapes and textures.
Agapanthus plants used to fill the narrow strip between the retaining wall and the footpath. They looked fabulous but were spilling over on to the footpath to the extent that something had to be done about them.
The owner decided to remove all plants, and would like to replant the area with something that is low maintenance, ground-hugging, and weed-suppressing without resorting to weed-mats, stones or nuggets.
One option is to cover the entire strip with a single ground-covering species. Another, more interesting option is to create a rhythm using a combination of a limited number of plant species, each with a particular texture, shape, and colour.
In the drawing, a pair of round shrubs is alternated with a group of small flax-like plants with a ground-cover in the foreground. Pittosporum tenuifolium 'Golf ball' grows into a ball-shape without training, and can be kept small with an occasional trim. Alternatively, Hebe odora (= Hebe buxifolia: box-leaf Hebe) or Buxus sempervirens (English box) can be used here. The small flax in the drawing is Phormium 'Jack Spratt', a dwarf plant with very dark brown foliage. The remaining space is planted with Scabiosa caucasica (pincushion flower). This low-growing evergreen perennial is an excellent ground-cover, quickly filling the available space. A trim once a year with the garden shears to remove spent flower stems is all the maintenance required for Scabiosa. Other possible ground-covers include Ajuga (bugle), Heuchera (coral bells), and Pulmonaria (lungwort).
On a conceptual level, the rhythm consists of balls alternated with two adjacent lines. Planting across a narrow bed (or, as in this case, planting some parts as wide as the bed, and planting across the bed in other parts) makes it feel wider and shorter. Lengthwise planting (such as two adjacent rows of plants without the rounded shrubs) accentuates the long, thin dimensions.