Tuberous perennials from South America, Canna are perfectly at home in our Sydney gardens. They belong to the plant family Cannaceae, of which they are the only genus, and they have links with other tropical plants such as gingers, banana trees, Strelitzia and Heliconia.
Previously spurned as vulgar, Canna have had a return to popularity in recent years and their attributes are now much appreciated. Flamboyant and showy, they bloom throughout summer and autumn, only fading when the cold weather really begins to set in around May. They give a tropical, exotic touch to our gardens, mingling happily with other summer flowers. The fleshy paddles of the canna leaves are an added bonus.
Flower styles vary from being gladiolus-flowered (flower spikes arranged close together on the stalk and large petals) to orchid-flowered (flower spikes arranged loosely with narrow petals). There are dwarf versions of cannas growing about 1m tall; medium ones are 1-1.5 m in height; tall ones are 2 m or more tall. The dwarf ones are suitable for modern gardens: they have been bred to be more compact and have more stems per rhizome. In small gardens Canna can successfully be grown in large containers, if kept well fertilised and well watered.
Canna come in a bewildering multitude of hues - ranging from bright and bold to subtle pastels - lending themselves to any number of colour schemes in the garden. Whilst their blooms are the main attraction, many also have stunning leaves. Some leaves are dark purplish or bronze, or have dark edges, setting off their flowers brilliantly. Others have foliage marked in different colours: yellow veined in the case of Canna 'Striata' (syn. 'Pretoria'); striped orange, red, green and bronze in the popular 'Tropicanna' (syn. 'Phasion'); blotched creamy-white in the cultivar 'Stuttgart': all giving scope for colour echoes with companion flowers to match these hues.
Canna need a full sun position and rich, moist (but well-drained) soil. They can also be grown as marginal plants at the edges of ponds. They need to be dug up and divided every few years in spring and replanted in soil which has been amended with plenty of compost and decayed manure. When dividing them, simply chop up the young, healthy parts of the tuber into pieces with some roots and growing points attached and discard the old gnarled sections. Canna will grow easily from seed, but will not necessarily produce the same coloured flowers as the parent plants.
Canna definitely benefit from being deadheaded regularly during the flowering season, as this will stimulate the production of more blooms. Only cut off the part that has flowered: new buds will be developing nearby. When a stem has completely finished flowering, with no more buds discernible, it can be cut back to the ground to allow a new stem to develop. They love regular applications of fertiliser throughout the warmer months, being greedy feeders. Some gardeners use tomato food as a fertiliser for them. Cut them completely back to the ground around June. Snails and slugs enjoy the fresh shoots in spring, so these need to be watched out for then. If the plants are well fed and watered, there should be few other problems. If leaves become infected with rust, I usually removed the whole stem and put it in the rubbish bin rather than the compost heap. Avoid watering the foliage, especially when the weather is hot and humid, as this will help to reduce the problem of rust, which usually appears in late summer.