Some of my very favourite plants for early autumn belong to the genus Plectranthus. Traditionally regarded as daggy plants only suited to the school fete plant stall, they are now given the respect they deserve.Though some do flower during other times of the year, early autumn is when they seem to be at their very best. Belonging to the mint family (Lamiaceae), they hail from warm temperate to tropical areas of the world (especially South Africa) and they can bring flowers and often attractive leaves into 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 disease and pest free. They also suit coastal gardens. What more could we ask of a plant?
Their two-lipped, often whiskered flowers are usually held on spikes above the foliage, which is generally soft and aromatic; some species have shiny, succulent leaves. Of the 350 or so species, there is a wide range of growth habits, from groundcovers to tall shrubby perennials. They are frost sensitive to varying degrees but cope well with Sydney winters. I generally prune my specimens back in mid-August, when they are also given some fertiliser. I replace them every few years from cuttings, which strike easily.
One of the tallest and showiest is Plectranthus ecklonii (ht 1.5 - 2 m) with its fuzz of large purple-blue feathers of flowers with pronounced stamens. It is one of the earliest types to flower, often beginning its long period of bloom in February. It mixes effortlessly with shade-loving plants with pink, white or burgundy flowers in bloom at this time, such as cane begonias, Japanese windflowers and Justicia carnea. Superb white and pastel pink forms of Plectranthus ecklonii are also around, offering great potential for attractive autumn flower schemes in shadier parts of the garden. 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.
Plectranthus zuluensis (ht 1.5 m) also has large flower-heads, which are a soft powder-blue colour. This is one of the species that flowers in flushes for a long time in Sydney gardens (from spring to early winter), but it is at its peak in autumn. Another of these floriferous plants is the lower-growing, shrubby Plectranthus saccatus (ht 1 m). which has jacaranda-blue, pouched blooms. It is an almost indestructible plant in the most inhospitable conditions of dry shade; it looks particularly attractive with lime-coloured leaves. It blooms from mid-summer till the end of autumn.
Hybrid plants sold as 'Cape Angels' result from a cross between Plectranthus saccatus and Plectranthus hilliardiae to form compact shrubs about 60-80 cm tall, with white, pink, purple and cerise-purple flowered forms, which are easily grown little shrubs which bloom over a long period. The well-known 'Mona Lavender' (ht 40-60 cm) results from the same cross. Smothered with a mass of prominent, upright lavender blue flower spikes set amongst purple-backed leaves, it is an eye-catching addition to the clan. These are all suitable for growing in a pot.
The silver plectranthus (Plectranthus argentatus, ht 1 m), is an Australian rainforest plant which is mainly grown for its large plush-velvet leaves, rather than its dainty lilac flowers, though they are rather pretty. It is one of the few silver-leafed plants to enjoy shade, and it looks beautiful in association with white flowers, such as windflowers or the lovely purple and silver foliage of Strobilanthes dyeriana (pictured at left). It will also grow very successfully in dry, sunny positions. A groundcover Plectranthus cultivar known as 'Nicoletta' has similar foliage, but it doesn't appear to be related to Plectranthus argentatus.
Also at groundcover level, Plectranthus ciliatus, ht 30-40 cm has an autumn veil of long spires of dainty lilac-tinged flowers across its purple-veined and purple-backed leaves. It will form an excellent carpet in the most uncongenial shady places under trees or shrubs, and is stunning when in full bloom. 'Nico' is an exceptional groundcover Plectranthus similar to this type, with larger and more deeply-veined leaves, and apparently derived from a different species. Another groundcover is Plectranthus verticillatus, sometimes called Swedish ivy, which grows to form a lush rug of shiny green scallop-shell leaves and has a froth of white flowers in autumn. All the groundcover types make excellent hanging basket subjects.
An excellent reference book on these plants is The South African Plectranthus by Ernst van Jaarsveld. For more information on the different sorts I grow, follow this link.They are such useful plants, and there are so many more species and cultivars which are grown overseas not yet available to us, including sumptuous gold-variegated leaf versions!
Plectranthus will be among the many plants for sale when the famous 'Huge Plant Sale' to raise funds for the National Breast Cancer Foundation takes place at 45 Parklands Avenue, Lane Cove North. It will run from 14 to 28 March 2021 in a COVID-safe way via the use of pre-booked, 30-minute appointments. Visit the Propagating Gardener website to make an appointment and see a list of all the plants that will be available for sale.
Blog originally posted on 31 March 2009; updated 7 March 2021.
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