The handsome leaves of Coleus blumei are available in a variety of colours, including many shades of red, purple and green. The plants are grown for their beautiful leaves, and the, which are not very decorative, are pinched out whenever they appear. If the flowers are left on the plants, the leaves lose much of their colour.
To grow coleus well a minimum temperature in winter of 10°C. (50°F.) is needed. At lower temperatures, or if plants receive a check in growth, they are likely to drop their leaves, but given a warm greenhouse, coleus are not difficult plants to grow.
It used to be the case that coleus raised from seed were of poor colour. This is no longer so and raising plants in this way. Rather than from cuttings, saves the bother of over-wintering old plants.
Seed should be sown in February or March in a seed compost and germinated in a propagating frame with a temperature of 16 to 18°C. (60 to 65°F.). The resulting seedlings should be potted singly in 3-in. pots of John Innes No. 1 Potting Compost as soon as they can be handled. When they have become well rooted in these pots they can be potted on into 5-in. pots using a similar compost.
Particularly attractive plants should be propagated by vegetative means, ie. by cuttings, as this is the only way in which they will come true to colour and form. The cuttings are made from young sideshoots taken from mature plants in spring or summer, inserted singly in small pots filled with sandy compost and placed in a propagating frame with a temperature of at least 16°C. (60°F.). Young plants have the most colourful foliage and it is wise to take cuttings several times in the summer so that there are always new plants available as the older ones are discarded.
Rooted cuttings are put first into 3-in. pots filled with John Innes No. 1 Potting Compost and are later moved into 5- or 6-in. pots.
Give the plants plenty of light to encourage good colour, and when temperatures are high, a humid atmosphere should be maintained by damping down the floors and stagings in the greenhouse. This will help to prevent the plants from flagging.
The tops of the shoots should be nipped out at intervals to induce a bushy habit.