Plectranthus ernstii is easy to grow, although relatively slow growing. It thrives as a pot plant and can be successfully grown in containers or shallow pans on windowsills. Shallow pots enhance its bonsai effect. This species is frost sensitive, it can withstand light frost but not moderate to severe frost. It can be grown outdoors in frost free, subtropical and coastal areas but in frost-prone areas it should be moved indoors during the coldest period of the year. It needs well-drained, humus enriched soil in a position where it will receive full sun, semi-shade or bright shade. Watering should be in summer, and care should be taken not to over water as this will cause the roots to rot. In the winter rainfall Western Cape it needs to be watered in summer and be planted in a very well-drained position, or grown in a container and taken under cover during winter.

Its attractive swollen stems and bonsai-look means that this species is most often grown in containers, but with its ornamental and aromatic foliage and attractive flowers it also makes a handsome addition to a mixed planting, and there is no reason why it can't also be used to good effect in the perennial border and rockeries, in frost-free areas. It should also do well in retaining walls and on steep rocky slopes.

Propagate by seed or by cuttings. Seed is best sown in spring or early summer in a well-drained soil mix containing two parts of sand and compost to one part of loam. Moisten the mixture, sow the seed evenly, and then cover lightly with a thin layer of sand to hold the seeds in place. Place in dappled shade in a warm place and keep damp. Germination occurs within approximately 21 days. Seedlings can be transplanted when they have developed two sets of true leaves.

Cuttings produce roots fairly quickly. Rooting is possible throughout the year, however the best time is in spring and early summer. Take softwood cuttings with 3 - 4 nodes. The rooting medium can consist of sand, perlite, vermiculite, peat or a mixture of any of these. Keep moist and shaded. The cuttings root fairly quickly in approximately 14 days under ideal conditions. Hygiene is of prime importance, when propagating from cuttings. Cuttings are prone to contamination by fungus this can be controlled by fungicide. Rooted cuttings can be transplanted after about a month and grown on in containers.

After planting out in the garden, plants must be well watered, at least twice a week until such a time as the plants are established. Feeding is also a very important aspect as it affects the flower and leaf quality. A balanced fertilizer can be applied every three months in the summer. Annual application of compost should be worked into the soil in late winter or early spring.

Prune P. ernstii frequently to maintain a neat 'bonsai' shape, although Plectranthus will grow and flower without being pruned, it is an essential practice which improves the quality of plants and flowering. Pruning is a renewal process and occurs in the natural habitat. Dead, diseased and weak growth is removed and the natural form is improved. The optimum pruning time is late winter, once the plants have finished flowering.

Several Plectranthus species are prone to root rot caused by soil-borne eelworms (Nematodes), and if affected, the plants need to be re-established from cuttings and planted in new soil. The green plectranthus caterpillars, slugs and snails can be troublesome at times.