This perennial Dianthus enjoys growing on the edge of a reatining wall in my garden

Plants from the Mediterranean region, on the whole, don't do very well for me, as they dislike our humid summers and mild winters, and really do need sharp drainage to succeed. In my heavy clay soil, they don't really last that long at all. However, quite by chance, I discovered that if the plants are placed along the edge of a raised bed in a sunny position, away from irrigation drippers, they can do quite well. They seem to relish the absorbed heat of the brick walls that retain these garden beds, and some of them spill over the sides, softening the hard edges in a most fetching manner. Some are groundcovers by nature; others are small shrubs that tend to loll a bit, so are suited to a spot where this can be a feature rather than a problem.

Erysimum mutabile has done well on the wall this year

Erysimum mutabile has done well on the wall this year

Some of these are in flower now - a few actually bloom for an extended period from late winter into late spring (some of them even longer), giving them great value over a long time. This year is the first time I have put a perennial wallflower in this position, and I have been enjoying the results. Erysimum mutabile is a bushy sort of perennial that tends to flop over so it suits a spot on top of a wall. It flowers for a very long time with its wands of clustered, rounded inflorescences that open pale yellow then age to mauve, blooming from July to November! An evergreen perennial Dianthus with hot pink flowers (shown at the start of the blog) also does very well and cascades over the side of the wall. It literally blooms all year round if deadheaded occasionally, and it consorts well with the wallflower. The perennial Lobularia (sweet Alice) is another Mediterranean plant that enjoys being near the side of a wall and grows over it happily. There are various pink, white and mauve cultivars of this relatively newly available plant in the 'Princess' and 'Stream' series, with names such as 'Snow Princess' and 'Lavender Stream'.

Convolvulus sabatius on the wall

Convolvulus sabatius on the wall

Nepeta racemosa (catmint) is another perennial with the same provenance that I have grown in a similar manner, though I don't have it at the moment. I have also in the past grown the silver foliage plant Artemisia 'Powis Castle' like this, and it did much better when lounging over the wall than trying to grow it in a border where it was swamped by other plants. Convolvulus sabatius is a trailing groundcover from the Mediterranean with shallow, funnel-shaped flowers usually of a milky-blue hue, but sometimes seen in darker blue colours or white. It looks at its best growing over a retaining wall. The prostrate form of rosemary is also an excellent plant to grow near the edge of a wall, and it will sport its bright blue flowers in late winter and early spring.

Eventually these perennials do need to be replaced by a fresh cutting, but they are well worth it, if you have a retaining wall for them to grow over. Gardeners in cooler inland areas or parts of Sydney that have less humidity will have more success than I do in growing these plants in ordinary garden beds, but they still do like to have good drainage and plenty of sun.

Ivy-leaved Pelargonium growing over a wall in the garden of Robin Diehm in Sydney

Ivy-leaved Pelargonium growing over a wall in the garden of Robin Diehm in Sydney

Other sorts of plants from different places that also like very well-drained soil can also do just as well when grown at the edge of a wall to tumble over. A number of South African plants fall into this category: silver Helichrysum petiolare is a favourite, as are ivy-leaved Pelargonium hybrids. I would be interested in trying a few other South African plants that don't do that well in other parts of my garden where the soil is not that free draining, such as Osteospermum (sailor boy daisies) and Felicia, with its cute little blue daisies, which I have never managed to grow successfully. Australian native groundcovers that like good drainage are also a possibility: for example, Scaevola species and cultivars and Myoporum parvifolium

Pink form of Linaria purpurea

Pink form of Linaria purpurea

More upright plants that enjoy a drier soil can be interspersed with the cascading sorts, to provide a contrast of form: some examples include Lychnis coronaria, Linaria purpurea, small Marguerite daisies, statice and tall bearded irises.

Finding the right niche for a plant is much of the fun of gardening!