A plant which is grown for its colourful foliage is the codiaeum, or croton. It is by the latter, outdated, name that it is still, perhaps, best known. The colouring of the foliage varies with the variety and there are also variations in leaf shape – some are long and strap-like while others are more rounded.
To grow codiaeums successfully a minimum winter temperature of 13°C. (55°F.) is needed. In summer. Temperatures can rise to 24°C. (75°F.). provided a humid atmosphere is main tained. The colour of the leaves is more intense in good light but it is wise to provide some shade against strong sunshine.
As codiaeums age they tend to lose their lower leaves and the best way of obtaining young plants with foliage down tolevel is to air layer an older plant. This is done by making a cut. About l in. long, part way through a stem to form a tongue. The cut surfaces are dusted with hormone rooting powder and then surrounded with damp moss. This is enclosed with a piece of polythene and tied above and below with raffia or twine. The polythene prevents moisture evaporating from the moss. When roots are seen twining amongst the moss the new plant can be severed from the parent just below the new root system.
The roots at this stage are rather brittle and they must be handled carefully. Put the new plant in a 3-in. pot of John Innes No. 1 Potting Compost without removing the moss and keep it in a warm part of the greenhouse until more roots have developed. Later, move to a 5- or 6-in. pot filled with John Innes No. 2 Potting Compost.
Codiaeums soon fill their final pots with roots and to keep them growing well they should be fed each week with a soluble or liquid fertiliser.
Instead of airplants, cuttings can be made from the ends of young shoots. Do not remove too many of the lower leaves otherwise the new plant will have a bare stem. Cuttings root without difficulty in pots of sandy soil in a propagating frame with a temperature of 18 to 21°C. (65 to70°F.).
A careful watch should be kept on the plants for signs of such pests as mealy bugs and red spider mites. The latter increase rapidly in the hot conditions which codiaeums enjoy. Regular sponging of the foliage with a white oil emulsion insecticide will help to keep the plants clear of these pests and it will also enhance the appearance of the foliage.