Zantedeschia - The Arum Lily which now it has been hybridized, is available in a multitude of colours other than the pure white original. We distinguish between the two basic types of hardy and tender. The hardy types are normally referred to as Arum Lilies, whilst the tender varieties - which can still be planted outdoors for the summer - are grouped as Calla Lilies.
Arum Lilies grow from tuberous roots or rhizomes, and the two main types of Zantedeschia aethiopica and varieties, together with Zantedeschia pentlandii and cultivars are the hardiest – being classed as bulbous perennials. They have erect or semi-erect stems of flowers and foliage. The flowers of the Arum Lily are the main attraction, but the leaves are also we worth considering for any planting scheme where Zantedeschias can be suitable grown.
The Zantedeschia aethiopica types are reliably evergreen only in the mildest of areas. Even then the foliage may be blackened by a mild frost. Z. pentlandii is not normally evergreen, but dies down for winter and re-emerges in early spring.
Spring and summer flowering with white, cream or yellow erect open trumpet flowers on the two types herein mentioned. There are many other colours available, but normally with a lesser degree of hardiness. Most of the coloured varieties are referred to as Calla Lilies; though of the same family Zantedeschia.
Hardy Zantedeschia can be bought at most times of the year as container grown plants at the local garden centre. These can be planted right away with the planting soil hole to be the same level or a little lower than the container plant. Do not plant too deep.
The other option is to buy the dried bulbs (rhizomes) as loose or pre-packed bulbs in the dormant season – autumn to late winter. Plant these just slightly below the surface with just a dusting covering of soil over the top, or a thin layer of mulching material.
The tender varieties in the Calla Lily group – normally brightly coloured – should not be planted until frost has finished in the spring. If bought in autumn or winter, they should be kept dry and cool until they can be safely planted after frosts.
If not planted at the water’s edge of pond or stream, a damp or moist area is preferred with either full sun or dappled shade. Arums can be grown quite well in full shade as foliage plants – very attractive – but with fewer if any flowers. A humus-rich soil is ideal or at least a good helping of organic matter when first planted.
Keep well watered throughout the summer and do not allow the plants to dry out. This is particularly the case after flowering has ceased, for the rhizomes will then continue to develop, ready to produce more flowers the following year. Watering can be supplemented with two-weekly liquid feed – tomato food is ideal formula - or a good dressing of bonemeal each spring.
All types are susceptible to aphids – greenfly in particular, and sometimes slugs in early spring.
Sowing ripe seed in late summer is one option – but may be two tears to get flowering plants.
Normal perennial division of the rhizome roots in early spring is a good way to control the spread and to provide new plants which will flower the following year – or possibly the same later the same year.
The hardy Arum lilies normally flower for a long period starting late spring until mid summer. They can also be ‘forced’ to ensure flowering at Easter (variable) in which case they can live up to one of their common names of Easter Lily.
For flowering at Easter, new corms of Zantedeschia aethiopica should be placed in a container of peat-based or organic compost in early or late December – depending upon the date of the following Easter. Keep in light, airy, frost free place and start feeding with general liquid fertiliser only when the foliage is in active growth, and then only every two weeks.
The plants can be moved to slightly warmer or cooler places to gauge the growth pattern and timing for Easter flowering. (It takes experience to get it right every time, so may be hit or miss depending upon your care and expertise!)