Plectranthus fruticosus; Forest Spur-flower “Avoca”, Spoorsalie, Muishondblaar, Vliebos (Afrikaans); cabhozi (Siswati); iNkungwini (Zulu)
Spur Flowers belong to the mint or salvia family and when the leaves are crushed, almost all have a distinct smell of one mint or another. This family of plants is the one group that the visually impaired can identify with certainty just by crushing a leaf and sniffing.
Common names vary from Spur-flower, with all its adjectives of “common”, “forest” or “purple” to “stoep jacaranda”! I'm told that the Afrikaans common name of “vliebos” is derived from the use that some Plectranthus are put to and that is to repel insects by crushing the leaves and releasing the volatile oils that drive insects, especially flies, away. I have seen Zulu herdsmen and people walking through forested areas like Nkandla, Qudeni and Ngoye Forests using sprigs of this species and P. ecklonii as flywhisks. The Zulu name I have for Plectranthus is iNkungwini, which tends to be a generic name for the group of plant species that form shrubs in the forests around Durban, and they are most commonly the purple spur-flower - Plectranthus ecklonii, and the forest spur-flower - P. fruticosus.
The “Avoca” form is a soft-wooded perennial that grows well and rapidly in the summer. They need a dormant period in the winter after flowering, and this is the time to prune the taller upright species. Flowers are produced in the early winter. These plants are short day plants - that is plants are triggered to flower when the day length shortens. They are superb herbaceous border or large bedding plants if used up against a wall in the shade, or under the shade of large trees.
This “Avoca” form has a tougher demeanour about it, in that it will grow in full sun without too much trouble. I have used it on a dry, sunny roof garden where it does not get that tall - not much more than a metre high - but the flowers are concentrated and are very pretty, as the winter begins to settle in on us.
This is a group of plants that are prone to insect attack, especially the sucking insects like scale and mealy bug, but with optimum growing conditions, these pests can be kept to a minimum. Keep the plants vigorous by pruning out old stems and encouraging new shoots - this needs to be done in the late winter. Plectranthus usually live in damp and shady areas so don't use them in the full sun unless they are the succulent species.
Propagation of Plectranthus is best done by cuttings - either semi-hardwood cuttings in early spring, or soft tip cuttings at any time in the year. Some species seed themselves but most nurserymen that I know just simply make cuttings.
As a wildlife attractor, this species is a good cover or shelter plant if planted in dense enough groups. I have found the Bleating Bush Warbler (or to use its more recent name, the Green-backed Camaroptera) use the leaves of this species to sew its nest into. When in flower, this species is visited by every honeybee and non-honeybee pollinator in the area. In our local forests when this species is flowering, just pull up a deck chair and watch how many insect species visit the flowers - my best count to date is about 30 species in just over an hour.
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