About the genus
There are many plant families that only have a small number of true succulents. Most Plectranthus and Coleus species (Lamiaceae, sage/mint family) are not succulent but the dozen or so species that have a degree of succulence, have two features exceptionally rare in the succulent world, namely blue flowers and an intense fragrance. With recent DNA studies, a good number of Plectranthus have been moved into Coleus, which has resulted in plants being available to purchase with both names.
The first widely distributed species by the ISI was Coleus amboinicus (as a Plectranthus), which was common in collections at the beginning of the century. The most succulent species is Plectranthus ernstii which, if treated like a bonsai, produces some fascinating shapes.
All species have intriguing inflorescences which produce blue or sometime white flowers. If lightly crushed, the leaves are highly aromatic, smelling like cough medicine or bubble bath. In fact, many species contain a muscle-relaxant used in bath products. Crushing a few leaves in the bath can be very efficacious.
How to grow them
These are tropical plants from eastern Africa, Madagascar and Socotra so they need winter warmth. They can be kept alive in a greenhouse where the minimum temperature does not fall below 5°C, where they should have a dry winter, but they perform much better as house plants. In the wild they are often protected by larger shade-providing plants but in cultivation they can take a lot of sun if not too near the glass.
Plectranthus ernstii is a woody, caudex-forming plant from South Africa. In order for a caudex to develop, the plant should be cut back regularly. Alternatively, if a caudex is not desired then the luxuriant growth can also be enjoyed. The plant can also be cultivated very easily as a bonsai as it offers many design options due to its vigorous growth and it easily forgives pruning mistakes.
The plant only needs to be watered moderately and the soil should be allowed to dry in between. The water requirements can be ascertained by the consistency of the leaves: if the leaves are hard, the plant does not need water, if the leaves are soft, you can water a little bit and if the leaves are limp and droopy, then water right away. You can fertilise once a month with an all-purpose cactus or succulent fertiliser, but if you repot regularly, then fertiliser is not necessary. The small purple flowers are formed on extending inflorescences, and it begins to bloom in April and its flowering period extends continuously into October. The flower stalks should be removed at the end of October and the plant should be cut back. Water less in winter and protect the plant from excessive dry air, and then in spring, when active growth begins, water again moderately and repot if necessary.
To propagate, the succulent species strike well if dried cuttings are placed in a standard cactus compost and they do not require any fertiliser as this can cause them to bolt and lose their compact nature.
Photos by Ray Stephenson
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