Plectranthus is an Old World genus of about 350 species inhabiting warm tropical and subtropical climates principally in the southern hemisphere. Its range extends from sub-Saharan Africa through Madagascar, India and the Indonesian archipelago down to Australia and some Pacific islands. Plectranthus is the largest South African genus in the mint and sage family (Lamiaceae), with 44 species natural to our region, most of which occur on the eastern side of the country.
A French magistrate and keen botanist, Charles Louis L’Héritier de Brutelle, was the first to describe the genus Plectranthus in 1788 based on P. fruticosus as type species. The Scottish botanist Francis Masson, a dedicated plant hunter for the Royal Botanic Gardens, Kew, on a joint plant collecting expedition with Carl Thunberg to the Cape in 1774, had collected seed from the wild and sent it to William Aiton who raised the seedlings in the glasshouses at Kew. L’Héritier saw the plants and realised that they represented a new genus which he named Plectranthus. Plectron = spur and anthos = flower. He may have been a bit hasty, however, as he later discovered that his new species is in fact the only member of the genus that actually has a spur.
Among the South African members of the genus are some of the showiest garden plants providing a mass display of colour in late summer and autumn. Colour selections range between pink, purple and white with many shades in-between. There are two species which do have yellow flowers but they are not good garden plants and their flowers are too small to be attractive.
Plectranthus are noted for their aromatic leaves when crushed or even brushed against, and the variety of aromas is as diverse as the genus itself. Plectranthus flowers produce large amounts of nectar, attracting many insects which transfer pollen between flowers.
Plectranthus are easily cultivated and require little extra attention or special treatment. They enjoy well-composted soils, and as a rule thrive in semi shade or cool positions on south facing aspects. They are ideally suited to growth under the shade of trees. They are generally shallow rooted and enjoy adequate water but they do store water in their stems and are resistant to prolonged periods of drought. Plectranthus are often grown for their attractive foliage, flowers or both and vary in their growth forms from dense prostrate ground covers to sub-shrubs and large shrubs.
Although they are frost tender they are usually grown in shady protected places and as such are afforded some protection from frost. Due to the fact that they all flower at the end of the growing season frost does not affect flowering. If the plants are affected by frost they can be cut back at the end of winter and will grow out rapidly. Once the plants have been established for a year or more they become woodier at the base and are more resistant to frost damage.
Most of the shrubby species make better, more dense and attractive shrubs if they are pruned back to between 1/3 and 1/4 of their height, at the end of winter before the new growth begins for summer. The ideal time to dress the soil with a thick layer of compost or organic mulch and an application of balanced fertilizer such as 2:3:2 is straight after pruning. Ground cover species rarely need to be pruned, other than occasional cleaning up of old growth and flower spikes.
The ground cover species often have very attractive foliage and form dense attractive carpets from 150mm to 450mm thick, which burst into flower in autumn. They root readily at the nodes wherever they touch the ground, and will form dense mats in a relatively short time.
Shrubby species vary in height from 50cm to 2m and may be planted en-masse or as single individuals. Once again most species enjoy shade but there are a few which can endure full sun.
Plectranthus are exceptionally easy to propagate and can be produced very easily with little special treatment. Most propagation is done from cuttings during the early part of summer and spring. Although the cuttings will root at any time of the year, they have a long summer ahead to establish if they are propagated at this time. Cuttings may take the form of soft-wood or semi-hardwood, but tip cuttings are usually the best.
The cuttings should have at least two nodes and the leaves should be removed from the lower portion. Rooting hormone is usually not necessary and has been known to cause the cuttings to rot. The cuttings should be inserted one third of their length into clean double washed river sand and kept in a warm shady place and not be allowed to dry out.
A FEW FAVOURITE SPECIES AND CULTIVARS
Plectranthus fruticosus (Common name: blue spurflower)
The striking new cultivar, P. fruticosus ‘Liana’, is distinct in that its flower colour is a dark blue-mauve, and in that it tends to have its flowering peak a few weeks later than the other cultivated forms of this species. Its semi-woody well-branched perennial growth habit results in a neat and dense rounded shrub around 1m - 1.5m high.
The inflorescence is in the form of an erect, branched panicle arising from the tips of the branches and in the axils of the uppermost pair of leaves, each panicle reaching up to 300 mm long and supporting approximately 600 flowers, with 6 flowers at each node. The calyx at the base of the flower is green, fading to purple at the mouth, 8 mm long at flowering and enlarging to 12 mm after the flower has dropped.
This cultivar is also distinctive in its growth requirements in that it grows most vigorously when it receives a fair amount of direct sun. It will tolerate shade happily but the growth rate will be much slower and the flowers will be paler. In nature the plant will survive for about 5 years but this can be increased in cultivation through regular pruning.
Plectranthus ecklonii (Common name: large spurflower)
Plectranthus ecklonii is a soft, erect, fast growing shrub to 3 metres tall. The leaves are arranged in opposite pairs on the square stems, the latter with tufts of purplish hairs along the nodes. The ovate to elliptical leaves are fairly large 75 - 190 x 35 - 115 mm bearing a wedge shaped base and acute apex.
In the garden P. ecklonii is an attractive and popular garden subject. Mass planting of the blue, white and pink cultivars are very striking. P. ecklonii is best grown in partial shade. It is recommended for gardens where frost is not too severe. In colder climates it can be grown as a container house plant indoors. P. ecklonii is a fast growing pioneer shrub and very suited for shady gardens. It will flower profusely the first season after planting. Plant about 60 cm apart. Prune back hard after flowering during midwinter.
There are three available cultivars: ‘Medley-Wood’ the common garden cultivar with blue flowers; ‘Tommy’, with white flowers; and ‘Erma’, with pink flowers.
Plectranthus verticillatus (Common names: gossip spurflower, money plant)
Plectranthus verticillatus is a perennial semi-succulent ground cover native to woodland and forest margins in southeast Africa. It has long been a popular garden subject in many parts of the world, both for its attractive foliage as well as for its delicate white to pale mauve flowers.
The popular “Swedish Ivy” pot and basket hanging plectranthus is not P. verticillatus, as it is sometimes referred to in the USA, but P. oertendahlii from the forested coastal river gorges of KwaZulu-Natal. The latter is characterised by variegated leaves with silvery markings.
White, pale mauve, or pale pink flowers appear sporadically throughout the year in gardens but more abundantly in spring and late autumn.
P. verticillatus is a nursery favourite in warmer areas of the world. A number of commercial cultivars, including several variegated forms, have been developed here and overseas — ‘Barberton’, ‘Blyde’, ‘Eureka’, ‘Freckles’, ‘Gossip’, ‘Malelaan’, ‘Money Maker’, ‘Pink Surprise’, and ‘Ubombo’.
Plectranthus ‘Mona Lavender’ (Common names spurflower, Mona Lavender)
Plectranthus ‘Mona Lavender’ is a hybrid developed at Kirstenbosch Botanical Gardens that is becoming a hit around the world! P. ‘Mona Lavender’ is a quick-growing, herbaceous, perennial shrub reaching up to 75 cm in height, forming a lovely, rounded, dense bush.
It has dark green, glossy leaves with intensely purple undersides and sprays of lavender flowers dashed with purple markings.
It flowers very unpredictably, but does well in shortened daylight, which starts in autumn, but depending on how old the plant is and how much it has been pinched back, flowering can be extended right into early summer.
The plant is being very effectively commercialized by the Ball Horticultural Company based near Chicago in the USA.
‘Mona Lavender’ is a pleasure for any gardener as it is relatively adaptable and trouble free. It does very well in either shaded or partly sunny positions. When it receives sun it tends to stay smaller and more compact and the leaves exhibit a much more intense colouring - especially on the purple undersides of the leaf.
The plants enjoy being pinched back to induce better branching and compactness. They make a great bedding plant and look good when they are planted en masse or as individuals in an existing bedding display. They also make good pot plants which can be moved around as needed and will fill a 25cm pot in a matter of months.
They enjoy feeding too, which should be carried out at any time but preferably not before or during flowering. The fertilizer may consist of a general all-purpose 2-3-2 as a granular or liquid feed - be sure to water it in well as it is easy to burn the tender roots, or use a purely organic fertilizer to avoid this.
One of the only downfalls of ‘Mona Lavender’ is that, like most Plectranthus, it doesn’t tolerate very cold conditions, although it has been known to survive light frosts. If you live in an area prone to winter frosts then plant it in spring and it will flower in the autumn before the winter frosts take their toll. For all parts that don’t receive heavy frosts, it can be planted at any time of the year.
Plectranthus zuluensis (Common name: Zulu spurflower)
This is a handsome, softly erect shrub with velvet textured leaves and striking dark purple flowers which make Plectranthus zuluensis a winner for those difficult shady areas in summer rainfall gardens.
P. zuluensis is an erect or sprawling, soft shrub up to 2m high, with much-branched, four-angled, hairy stems which are velvety to the touch when young. Soft, semi-succulent leaves are ovate with coarsely toothed margins and covered with tiny, colourless glands.
In its natural environment the species is often common along stream banks and deep river gorges in humus-rich soil and in shady or semi-shady areas on the margins of semi-coastal, subtropical forests. It is best suited to gardens in warmer, frost-free areas.