Download Article 111 BioControl 11 - Botanical Society of South Africa

Weeds in our Area (Part One Hundred and Sixteen)
By Bob and Ena McIntyre – Garden Route
Plectranthus comosus (Abyssinian coleus, woolly plectranthus)
The Plectranthus is a member of the Mint family (Lamiaceae) which has about 350 known species
occurring world-wide ranging throughout Africa, India, Australia and even Japan. Of the 53 species
in South Africa and Namibia it is those from the Eastern Cape and KZN that are most suitable as
garden subjects. Plectranthus is not only very easy to grow, the plants also tolerate a wide range of
conditions, from full shade through to full sun and from damp to dry. Unfortunately Plectranthus
comosus from North Africa - hence its common name Abyssinian coleus - has become a problem in
some areas of South Africa including the Garden Route.
Woolly Plectranthus, a category three weed, grows without any effort, is extremely hardy and can
make an eye-catching display when in flower all of which contributes to making it a lowmaintenance favourite with gardeners. To its discredit is the fact that it readily out-competes our
local indigenous plants and is therefore very
detrimental to our natural vegetation. Isolated
infestations can be found from the Western
Cape through KZN right into Limpopo.
Identification: Woolly plectranthus is a robust
erect shrub up to 3 meters tall with a woody
base. The stems and leaves are densely woolly.
Leaves are large, usually more than 100mm long
and 47mm wide, light green above and greygreen below. The flowers - borne in a terminal
spike-like raceme between 200-300mm long appear between March and September and are
deep blue or mauve. The individual flowers are
up to 20mm long. Old unattended specimens
tend to look really untidy and scrawny.
Control: As mentioned above, this species grows at the drop of a hat and is extremely hardy.
Exercise great care when removing the plant as pieces of stem left behind will take root and grow.
There is no herbicide registered for the control of Woolly plectranthus. Cutting back promotes
coppicing; therefore the cut stump has to be dealt with. Either remove entirely or treat the stump
in some other way. If possible all parts of the plant should be burnt if incineration of garden refuse
is permitted in your area. Shredding is another option.
Substitutes: Any of our local plectranthus species (Plectranthus ecklonii,– pink and mauve and
Plectranthus fruticosus - white) will make a worthwhile replacement and there are several more
exceptionally beautiful varieties ranging from those suitable for pots and flower boxes (P. saccatus)
to small and medium shrubs (P.ciliatus) and ground covers (P.madagascariensis, P.verticillatus).
References: Alien Weeds and Invasive Plants by Lesley Henderson, Copyright © 2001 Agricultural
Research Council. The Southern African Plectranthus by Ernst van Jaarsveld, Copyright © 2006.