Tag Archive: pond plants

Zantedeschia aethiopica
Zantedeschia aethiopica

Zantedeschia is a genus of about 8 tuberous or rhizomatous perennials, found in swamps or moist soils at the margins of lakes in southern and eastern Africa. The name of the genus was given as a tribute to Italian botanist Giovanni Zantedeschi (1773–1846) by the German botanist Kurt Sprengel (1766–1833).

Zantedeschia fall into two main types:

  • hardier outdoor forms (Z. aethiopica and Z. pentlandii ), often called arum lilies, with striking white flowers (these are in fact ‘spathes’ – a coloured bract or leaf- wrapped round a thin, creamy yellow column, or spadice); and

  • the more tender hybrid forms, typically with white-spotted leaves and pretty yellow, orange, pink or dark purple spathes (Z. elliottiana and Z. rehmannii  hybrids), which are borne in spring  or summer.  Z. elliottiana have broadly, heart shaped leaves, most with a covering of translucent white dots and usually yellow spathes, whereas Z. rehmannii have mid to dark green, lance – shaped leaves, rarely spotted, with white to pink or dark purple spathes. These are often called calla lilies.

However, Zantedeschia is neither a true lily (Liliaceae) nor an Arum or a Calla!

It has often been used in paintings, and is visible in many of Diego Rivera’s works of art (see The Flower Vendor, amongst others). It was a favourite subject of the painter Georgia O’Keefe.

Zantedeschia aethiopica
Zantedeschia aethiopica

Z. aethiopica is  the most common form in British gardens, grown as a marginal aquatic plant. This is a wonderful architectural plant for pond margins in areas that do not suffer from very hard frosts. The leaves alone are an attraction. They are large, 40cm (16in) long, and arrow-shaped, and a bright, glossy green with distinct veins. However, arum lilies are mainly popular for their serene, white flowers.They make superb, classy cut flowers.

Grow the arum lily as a water plant, planting it into a special aquatic basket, in water up to 30cm (12in) deep. Or you can plant it into moist soil around the pond, protecting it with a deep mulch over winter. The Royal Horticultural Society have given it their prestigious Award of Garden Merit.

In frost – prone areas they should be covered with a deep winter mulch. Where temperatures fall below 10 celsius more tender arums can be grown in a warm greenhouse  or as houseplants, or can be planted out in summer in a sunny site. Zantedeschia can be propagated by seed or division (divide in spring).

For early flowering plants at Easter, plant the rhizomes in December. Keep in a light, cool place at a temperature of 16°C (61°F) by night and 18°C (65°F) during the day. Feed fortnightly with a high-nitrogen fertiliser when in active growth but withhold feed during flowering. A high potassium feed such as a tomato fertiliser can be given once a week after flowering.

Both types of Zantedeschia can be grown in containers. When planting, use a loam-based compost such as John Innes No. 2 and plant the rhizomes (underground stems) just showing at the surface of a container with the eyes of the rhizome uppermost.

Water freely through the summer and feed with a balanced liquid fertiliser every two weeks until the flowers have faded. Zantedeschia are generally pest and disease free, but can suffer from winter cold unless protected.

Zantedeschia species are poisonous due to the presence of calcium oxalate. All parts of the plant are poisonous, typically producing local irritation or a burning sensation in the mouth and occasionally vomiting and diarrhoea. However leaves are sometimes cooked and eaten.

Sources and further information:


RHS guide to growing Zantedeschia

Lakeside guide to growing Callas

Gardeners’ World guide to Z. aethiopica

Kew Gardens- Z. aethiopica

This concludes my series ‘A-Z of Perennials’, started last year. I hope you’ve enjoyed it and will also like my new series- ‘A-Z of Garden Trees’, coming soon!

Old School Gardener

Are your Water Lilies taking over?

Are your Water Lilies taking over?

This week’s gardener’s question is about dividing the tubers of water lilies and comes from Paul Theother of South Mimms. He asks:

“I have a garden pond which is so full of water lilies that the other plants are being swamped. Can I divide and repot them or is it necessary to start afresh?”

Yes Paul, now’s the time to remove the plants from the pond and divide them. You can do this at any time between April and June. Cut the tubers into smaller pieces so that each contains a number of ‘eyes’ from which the new leaves are produced. Tie back the long, straggly roots and plant them individually in large baskets to help contain their growth, using aquatic compost and gravel to help to weigh them down. They should be put into the pond at a depth where they can send their flowers to the surface – this will depend on the variety and maturity of the plant.

Another plant that benefits from dividing, and which can yield many more plants as a result, is the Flag Iris.

If you want to do this then wait until after they have flowered. Lift the rhizomes (the tuberous roots), with a fork and discard the older pieces. The outer, younger growth will provide you with your new plants – this is where most of the new horizontal growth will occur. Having cut away the the old part of the rhizome to leave only a small part of this season’s growth and with some roots and leaves attached, trim the leaves back just above the point where they begin to spread out, leaving a small fan.

Replant or pot these up in soil which has had organic matter added – but don’t overdo it. Leave the top of the rhizome visible, so that they look rather like a crocodile in a lake! If you have a windy garden you can plant them slightly deeper – or try to place them somewhere where they won’t be toppled or suffer windrock. The shortest varieties of tuberous Iris can be left undivided for several years, whereas taller varieties should be divided regularly after flowering – usually every third year.

Here’s a picture gallery from Wikihow.

Iris 'Samurai Warrior'- the closest breeders have come to a red Iris

Iris ‘Samurai Warrior’- the closest breeders have come to a red Iris

Further information:

Lifting and dividing irises

A-Z of Perennials: I is for Iris

Do you have a gardening question I can help with? If so please email me at: nbold@btinternet.com

Old School Gardener

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