Plectranthus is a genus of about 350 species of annuals, evergreen perennials, semi-succulents, and shrubs from Africa, Madagascar, Asia, Australasia, and Pacific Islands. They are useful in a cool greenhouse or outdoors in hanging baskets, containers, or sunny borders. The foliage is often ornamental, with decorative margins and a fuzzy appearance. Flowers are small but are usually borne in good-size racemes of tubular, 2-lipped flowers in shades of purple, pink, white, or blue.
Growing Conditions and General Care
Plectranthus are easily cultivated and require little extra attention or special treatment. They enjoy well-composted soil and, as a rule, thrive in semi-shade on the south-facing positions. They are ideally suited to growth under the shade of trees. They are generally shallow rooted and enjoy adequate water, but they do store water in their stems and are resistant to prolonged periods of drought. Plectranthus are often grown for their attractive foliage, flowers, or both and vary in their growth forms from dense prostrate ground covers to sub-shrubs and large shrubs.
Although they are frost tender, they are usually grown in shady, protected places and, as such, are afforded some protection from frost. Because they all flower at the end of the growing season, frost does not affect flowering. If the plants are affected by frost, they can be cut back at the end of winter and will grow out rapidly. Once the plants have been established for a year or more, they become woodier at the base and are more resistant to frost damage.
Most of the shrubby species make better, denser, and attractive shrubs if they are pruned back to between 1/3 and 1/4 of their height at the end of winter before the new growth begins for summer. After pruning, it is the ideal time to dress the soil with a thick layer of compost or organic mulch and an application of balanced fertilizer such as 2:3:2. Ground cover species rarely need to be pruned, other than occasional cleaning up of old-growth and flower spikes.
The ground cover species often have beautiful foliage and form dense, attractive carpets, from 6 to 18 inches (15 to 45 cm) thick, which burst into flower in fall. They root readily at the nodes wherever they touch the ground and will form dense mats in a relatively short time.
Shrubby species vary in height from 20 inches to 6.67 feet (0.5 to 2 m) and can be planted en-masse or as single individuals. Once again, most species enjoy the shade, but there are a few that can endure the full sun.
Plectranthus are exceptionally easy to propagate and can be grown very easily with little special treatment. Most propagation is done from cuttings during the early part of summer and spring. Although the cuttings will root at any time of the year, they have a long summer ahead to establish if they are propagated at this time. Cuttings may take the form of soft-wood, semi-hardwood, but tip cuttings are usually the best.
The cuttings should have at least two nodes, and the leaves should be removed from the lower portion. Rooting hormone is usually not necessary and has been known to cause the cuttings to rot. The cuttings should be inserted one-third of their length into clean double washed river sand and kept in a warm shady place and not be allowed to dry out.
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