Plectranthus
Striking flower and foliage colours, multiple forms and an easy-care habit put plectranthus in the picture, writes DERYN THORPE
Grown for its colourful, velvety leaves and mass flower spikes, plectranthus is an unfussy, beautiful collection of plants for gardens and containers. These plants are a favourite at my place because of their versatility, and I especially appreciate those that thrive in dry shade, as well as the coloured-leafed coleus and hybrids with flower plumes, which provide the wow factor in pots and beds in autumn.
Coleus ( Plectranthus scutellarioides) has been grown since Victorian times for its velvety, coloured leaves. It has the most spectacular foliage of the genus, but others have variegated cream leaf margins, which brighten shady parts of the garden.
There are about 350 species of plectranthus, which is in the mint family (Lamiaceae). Plants originate in tropical and temperate areas, including Africa, Asia and the Pacific islands, and about 22 species are from eastern Australia.
Plants differ in form, and can be shrubs or perennials, some with glossy, fleshy foliage, others with soft hairs on aromatic leaves and stems. While they are renowned for doing well in shade, some varieties prefer to grow in full sun. All forms like free-draining soil and resent frost. Most flower in autumn, though you can get flowers through much of the year, except in winter.
care & cutting tips
Plectranthus prefer well-composted soils and adequate moisture, but they cope with a dry spell or root competition, especially species that store water in their succulent stems. Since they originate from areas that receive summer rain, they appreciate moisture during the warmest months.
Tip cuttings, taken with at least two nodes (where leaves grow from the stem), strike easily in moist potting mix, and the tropical varieties will root in a glass of water. Transfer
to potting mix when roots are about 4cm long. Take cuttings of glossy varieties at any time, except during winter in cold climates. These grow quickly and can fill a 25cm pot in a few months. The hairy-leafed varieties are best struck in autumn and spring.
The plants need an annual pruning after flowering to keep them dense. Stem tips of the trailing forms should be regularly trimmed to ensure they retain their compact shape, and to encourage branching.
Although plectranthus are relatively undemanding and pest-free plants, they appreciate an application of a complete fertiliser once a year in spring. Give them a dressing of compost, over the root zone, too, topped with bark or cane mulch.
Coleus, especially those that are overwintered in greenhouses, can suffer from downy mildew, so it’s best to water from below and keep air circulating.
all shapes and sizes
There is a wide range of groundcovers to choose from. P. oertendahlii is an African variety loved for its slightly succulent, variegated leaves with silver markings and deep red undersides, and the bonus of mauve or pink flowers from late summer to winter. It reaches about 30cm tall, and can be grown as a groundcover in the garden, or a trailing pot plant in a bright spot indoors.
The one I find the most useful is P. ambiguus, which gets to about 40cm tall and creates a dense carpet as it scrambles through dry shade beneath trees, where stems put down roots anywhere it touches the ground. It attracts little comment most of the year, then in autumn sends up striking spires of purple flowers that make it a highlight. I team this with the native silver plectranthus ( P. argentatus), which adds height and foliage contrast. Also from southern Africa and similar in growth habit is the oddly named Swedish ivy ( P. verticillatus).
Often used in hanging baskets, it has scalloped leaves and a lacy froth of white flowers, mostly in autumn. These creeping plants and similar fleshy varieties of plectranthus seed and root very easily, so they are potentially weedy in areas with warm, wet summers.
Cuban oregano ( P. amboinicus), also known as four seasons herb, is a groundcover that grows to about 50cm tall. Its edible foliage, which is good in meat dishes, is said to taste like a strong blend of thyme and oregano. It is also used medicinally in some countries. I grow a variegated form in part shade.
Pungent leaves are a feature of plectranthus, and few are as smelly as dogbane ( P. caninus). The unpleasant smell of its crushed foliage reputedly repels dogs and cats. It flowers best in full sun, grows about 30cm tall and 1m wide, and is almost indestructible. Its pretty, purple flowers look like lavender spikes, and appear on short stems, mostly in autumn. But their odour will not encourage you to pick a flower posy!
Shrub forms are mostly grown for their massed display of small, tubular flowers. Some have purple undersides to the leaves. Named hybrids, mostly crosses between P. saccatus and P. hilliardiae, are compact shrubs that make excellent container plants.
One of the taller forms is P. ecklonii, which grows up to 3m tall and about 90cm wide in semi-shade, and produces masses of purple, pink or white flower spikes in late summer and autumn. I have one that grows beside a frangipani, with clivea and purple tradescantia at its feet, but it also teams beautifully with Japanese windflowers ( Anemone x hybrida) and cane begonias, which flower at the same time.