Plectranthus are a semi succulent that can be used as a bonsai or accent and they are very easy to keep, hold a good shape and propagate easily too. There are over 350 species of Plectranthus and the majority originate from areas of Africa, Madagascar, India and Australia to name a few and they belong to the Mint and Sage Family (Lamiaceae).
The most common species used in bonsai is Plectranthus ernstii otherwise known as Bonsai mint or Bonsai spur flower as this has a fun striation to the bark of the caudex which fatten quickly with watering during the Summer months. However, be careful not to overwater as they can split if they grow too quickly plus excess watering can lead to root rot. The leaves are aromatic and they have small blue to purple flowers off a spike which bloom from late Spring through to Autumn. They do grow fairly slowly and are perennials and if grown as a bonsai still ensure to feed with a balanced fertiliser as this aids in maintaining a good leaf colour.
The leaves are heart shaped and soft to the touch and fleshy, they can be affected by red spider mite, mealy bug plus caterpillars so check regularly for pests and remove any you find. You can keep them in akadama or a succulent compost mix and they can get quite pot bound so need re-potting and this would be the time to divide up any clumps. Keep them in a warm environment throughout the Winter months in the UK as they are not tolerant of cold conditions or frosts and ideally on a windowsill indoors is ideal conditions or a warm greenhouse.
They also take well from leaf cuttings and respond well to regular pruning which does aid with reducing the leaf size by building up the density of leaves. Here are a selection of ones in development as accents and bonsai.