Plectranthus hail from warm temperate to tropical areas of the world (particularly South Africa) and grow in shadier parts of the garden under trees in very ordinary soil where many plants do not thrive. They grow quickly and are tolerant of drought and root-competition. They are perfectly suited to our Sydney climate and provide a significant contribution to the garden in early autumn.
One of the showiest is the Plectranthus ecklonii (known colloquially as tall spurflower) from South African forest regions, with its fuzz of large purple-blue feathers of flowers with pronounced stamens on a substantial shrubby perennial 1.5-2 m tall. It is one of the earliest types to flower, often beginning its long period of bloom in February, continuing till early April. It seems best in part or dappled shade. It mixes effortlessly with shade-loving plants with pink, white or burgundy flowers in bloom at this time, such as shrub and cane Begonia, Justicia carnea and Japanese windflowers , but also can be a good contrast to orange or red flowers in part or dappled shade, such as the so-called red justicia (Odontonema tubaeforme) or cane Begonia. The flowers are also effective partnered by gold or lime-coloured leaves that tolerate part-shaded areas such as golden Duranta, or the beetroot-coloured leaves of Iresine herbstii 'Brilliantissima'. Unlike most Plectranthus, which tend to scorch if grown in full sun, it is sun tolerant, and is an effective partner to Salvia, Canna and Pentas which bloom in sunny places through autumn.
Superb white ('Tommy') and pastel pink ('Erma') cultivars have become available in recent years, offering great potential for attractive autumn flower schemes in shadier parts of the garden, where their generous trusses in March and April lighten up the gloom. The misty, lacy fretwork of their flowers offers a contrast to bolder tropical blooms such as the huge pink or white angel's trumpets (Brugmansia species and cultivars), which continue to have flushes of flowers in autumn. They also mingle well with Camellia sasanqua or the ageing blooms of mop-headed Hydrangea. A massed group of the pink, white and purple forms all grown together can look very attractive.
They should be cut back fairly hard after flowering (or in early spring in cooler areas if there is the risk of frosts). It is possible to clip them back several times during spring and early summer to keep them more compact. They dislike hard frosts, but if grown under a canopy of trees, they will usually be protected from milder frosts. They enjoy being mulched and fed occasionally. They can be very easily propagated from cuttings in spring and summer. All Plectranthus need to be replaced by new cuttings every so often as they get a bit straggly and rather woody after a few years. They sometimes self-seed, but the seedlings are easy to remove. When severely stressed by drought, the plant will become very wilted and you will think it is dead, but will bounce back to life when it rains (or is given some water)!