Shady characters: Plectranthus

Tuesday, 31 March 2009

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 starting to be given the respect they deserve.

Belonging to the mint family, 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.

One of the tallest and showiest is Plectranthus ecklonii (ht 1.5 - 2m) 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 have become available in recent years, 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, which continue to have flushes of flowers in autumn. They also mingle well with Camellia sasanqua or the ageing blooms of mop-headed Hydrangea.

Another species of similar height is Plectranthus barbatus, with thick, furry leaves and long, bright blue spires of flowers, the bluest of all the Plectranthus. Lower growing, shrubby Plectranthus saccatus (ht 1m) has jacaranda-blue, pouched blooms, which are larger than most other plectranthus. It is an almost indestructible plant in the most inhospitable conditions of dry shade; it looks particularly attractive with lime-coloured leaves.

The silver plectranthus (Plectranthus argentatus, ht 1m), is an Australian rainforest plant which is mainly grown for its large plush-velvet leaves, rather than its dainty lilac flowers. It is one of the few silver-leafed plants to enjoy shade, and it looks beautiful in association with white flowers, such as windflowers and Hydrangea, or the lovely purple and silver foliage of Strobilanthes dyerianus. It will also grow very successfully in dry, sunny positions. A groundcover cultivar known as 'Nicoletta' has similar foliage.

Also at groundcover level, Plectranthus ciliatus, ht 30 - 40cm 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. Plectranthus verticillatus, sometimes called Swedish ivy, 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.

Hybrid 'Mona Lavender' (ht 40-60cm), which was released about five years ago, is a compact shrub, useful in smaller gardens. 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. A similar group of hybrid plants, sold as 'Cape Angels', comprises white, pink, purple and cerise-purple flowered forms, which are easily grown little shrubs which bloom over a long period. Plectranthus 'Coral Cloud' is another small cultivar (ht 40cm) with sprays of pretty pink spires in autumn.

An excellent reference book 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 - Please do let me know if you share my affection for these plants!