I have placed this plant under its common name of Arum Lily rather than its botanical name of zantedeschia because it is by the former that it is invariably known to gardeners, and because I believe that more people still refer to it as richardia (its outdated botanical name) than the current zantedeschia. However that may be. There is no doubt that the Arum Lilies (which incidentally are not related to the true) make splendid greenhouse perennials.
The Arum Lily most commonly grown is ‘Zantedeschia aethiopica, a handsome plant which is also known as Calla Lily, the Lily of the Nile (although it comes from South Africa!) and Trumpet Lily. There are also several yellow-flowered species including the deep yellow Z. pentlandii and the pale yellow Z. elliottiana, both of which are more tender than Z. aethiopica and so need more protection and slightly higher temperatures.
The Growth Cycle
Z. aethiopica makes a plant 2 to 2-1/2 ft. tall and the pure white spathes on long stems surrounding the trueare much in demand at Easter time for flower decorations.
The time to start this plant into growth is in July or August when the oldshould be shaken from the roots. At this stage it can be divided and about three roots or crowns can be accommodated in an 8-in. pot. John Innes No. 2 Potting Compost can be used and it must be worked in well amongst the roots. After a good watering the pots are stood in a sheltered place in the open but they should be taken into a light place in a cool greenhouse before there is any chance of autumn frosts – this is usually by the end of September. Until growth begins, water should be given sparingly. The temperature can be raised gradually to 13 to 16°C. (55 to 60°F.) as the plants develop if early flowers are needed, but they will be quite happy in a temperature of 7 to 10° C. (45 to 50°F.) if flowers are not needed so early.
Arum Lilies respond to feeding and once the pots are full of roots regular feeds of a liquid or soluble fertiliser every 7 to 10 days will help to produce good flowers.
After flowering, watering and feeding must not be neglected but in early June I like to give the plants a rest by laying the pots on their sides in a sheltered spot outside the greenhouse so that the soil is kept dry until repotting is done once again in August, and the cycle is repeated.
Greenfly can spoil the flowers but fumigation with nicotine shreds or BHC smoke pellets will soon deal with them. If reddish globules can be seen on the underside of the foliage the presence of thrips must be suspected. The use of a BHC spray, or malathion as an aerosol, a spray or a dust will be effective as a control.
Propagation is by division of the fleshy roots when repotting.