EXOTIC FOLIAGE ETCHED IN COLOUR
With vivid flowers standing tall above ostentatious leaves, cannas bring pattern and fire to plantings
AS THE SUN lowers in the sky, and nights become cooler and mists more frequent, the seasonal shift in the garden switches to pastel daisies set against fiery autumn foliage. Wispy grasses, laden with dew, arch over clumps of chrysanthemums and dark-eyed rudbeckias. Contrasting starkly against the diffuse clouds of blossoms, cannas thrust high above, with huge leaves in shades of green, purple and bronze, and large, flag-like blossom in luscious hues of orange, red and pink.
Cannas have been decorating our gardens for more than a century, and yet they still appear marvellously exotic: nothing else in the garden looks like them. But they are adaptable and easy to grow. Although they are evergreen in warmer climates, where winters are cold, they are replanted outside every spring, after the frosts have passed, and gain vigour and bulk through the summer months to reach a crescendo in autumn. It is now that the work earlier in the year pays dividends, with cannas at their ultimate height, their stems crowned in glorious blooms and the foliage lush and colourful, especially when they are backlit by the low rays of the autumn sun.
They can be slow to start to bloom, especially in cool summers, but as each new shoot reaches maturity, it will be crowned with flowers. So long as the plant is growing vigorously, it will continue to bloom. The flowers are brightly coloured and showy, but are not fragrant: perhaps a sign that they have developed for pollination by birds in their natural habitat rather than insects, although in the garden, the copious nectar may attract bees.
Unusual blooms
A close look at the flowers reveals that they are rather unusual. The blooms, set on top of the round ovary, have three tiny, scale-like sepals and three, small, narrow petals. What makes up the showy part of the bloom are not petals in fact, but some of the stamens, which are modified into petal-like, colourful structures, called staminodes. There are usually three, with a lower, narrow lip, or labellum.
If flowers are pollinated, round seed pods will form. These have three lobes and are covered in pimples. Green or purple in colour, the pods contain hard, pea-sized seeds, which give rise to the common name of ‘Indian shot’, a moniker referencing the West Indies, rather than India. Although not showy in the same way as some other seed heads, they can be cut for autumn flower arrangements.
From warmer climes
There are 10 species, all easily recognised as cannas, with their thick, creeping rhizomes beneath the soil surface, large, paddle-like leaves, and flamboyant flowers topping their stems. They are all native to tropical and subtropical South
“The tendency of most half-hardy flower garden plants is to flatness, and the grace of the cannas makes them valuable”
William Robinson, The English Flower Garden
America, although they have been spread to all warm areas of the globe and have widely naturalised. It is thought that Canna edulis has been grown as an edible crop in Peru for at least four millennia. Canna indica, with its red and yellow flowers, is the most commonly available species in the UK.
Although cannas have been known since the 16th century, they were not grown in Europe until the mid 19th century. Their potential as summer bedding plants in parks and gardens was quickly recognised, and hybrids were produced involving many species, including C. indica, C. glauca, large-flowered C. iridiflora, and C. warscewiczii. The early hybrids were raised in France, notably by Antoine Crozy, and later in Italy and Germany, and were developed for large flowers and height. By the end of the 19th century, there were more than 100 named cultivars, and by 1906, the RHS was trialling 270 types.
In recent years, since a revival of their popularity at the turn of the last century, breeding has turned to producing smaller, dwarf cultivars, more suitable for patio containers and modest borders. Longwood Gardens in the USA has been at the forefront of this work, but international seed companies have introduced new strains that can be grown from seed and will flower the first year: this is in response to the prevalence of canna virus, which has become a serious problem in the past 20 years.
Growth and new shoots
Cannas vary in height according to the cultivar, but height is also influenced by growing conditions and the age of the plant. Even tall cultivars will bloom at less than half their regular height if they are young or ill-fed. As plants mature, and the rhizome increases in size, each new shoot will be more vigorous. The majority of cannas will grow to approximately 5ft (1.5m) in average conditions, but some are significantly taller. Dwarf kinds may be just 24in (60cm) in height when in bloom.
Foliage can be green, bronze or flushed with beetroot red. The flowers are usually orange, red or yellow, although some are pink, cream or ivory.
If bought in growth, often with flowers, the plants will usually be considerably smaller than their ultimate height. New shoots are usually produced close to the existing shoots from the underground rhizome, but they can be 6in (15cm) or more away, and because there should be several produced each year, a canna with a single shoot when planted can have a dozen shoots, forming a clump 12in (30cm) or more across, by the end of summer.
As the rhizomes grow through the soil, they send up new shoots. If they are growing strongly, each one will produce a scape, or stem, carrying blooms. This can branch, and a succession of flowers is produced. Each bloom lasts approximately two days, and a stem can continue to bloom for a month. When the last flower drops, the whole shoot will eventually die, and it is best to cut this out at the base, although mere deadheading will keep the clump looking neat.
Best growing conditions
As cannas are native to regions much warmer than ours, they need as much warmth and sun as possible, although this should not be confused with drought conditions. Most disappointments with these plants are caused by poor growth: the result of insufficient water and nutrition.
When planting in borders, as much organic matter should be dug in as possible. Well-rotted manure, or even quite fresh manure, is suitable. Cannas are gross feeders, and anything that adds nutrients to the soil and helps retain moisture is beneficial. Cannas prefer acid soils, but will tolerate slightly alkaline conditions: thin, chalky soils should be avoided. The large leaves of cannas are prone to wind damage, so they will look their best in sheltered sites.
Cannas grow well in pots, provided they are well watered and fed regularly. A good multipurpose compost is suitable, especially if augmented by the addition of controlled-release
fertilisers at planting time. Cannas provide instant height on the patio and a long succession of colour.
Propagation
Cannas can be easily propagated by dividing the rhizomes. This is best done in spring, after they have been overwintered in a frost-free place. The soil should be shaken from the rhizomes and a sharp knife used to cut the clump into sections. To make good-sized plants, it is best to pot clumps with several shoots.
Varieties vary regarding the shape of their rhizomes. Some are compact, while others have long, thin rhizomes. Since they should be potted horizontally, the latter can be difficult to fit into pots, so shallow half pots can be useful, rather than deep ones.
Pests and diseases
Slugs and snails may attack young shoots in spring, often eating through the furled leaves, resulting in a line of holes. Aphids sometimes also affect young shoots early in the year, but are rarely a problem in summer.
The most serious problem, and one that threatens the existence of many old, established cultivars, is that of viral disease. There are two common ones that affect these plants: canna yellow mottle virus, which is spread from plant to plant via knives and fingers transferring sap, and bean yellow mosaic virus, which is transferred by aphids. Both cause stunting of the plants, discoloration of the flowers and pale streaks in the leaves. Because they have spread among commercial stocks, it is likely that dried rhizomes, bought in spring, will be infected, so it is better to buy growing
plants in summer, when any infection will be more visible. Although plants can live with the disease, it means they will become less productive, and since it cannot be cured, the best practice is to dispose of any affected plants.
Planting partners
Although cannas are ideal for pots on sunny patios and are most frequently associated with large foliage and vibrant blooms in subtropical planting schemes, they are just as suitable as dahlias to bring contrast and colour to any border.
October brings two major colour palettes to the garden: the pinks and purples of Michaelmas daisies and Japanese asters, and the fiery hues of rudbeckias, helianthus and autumn leaves. All have rather nondescript foliage and habit, and cannas, with their wide range of flowers and bold foliage, inject much-needed contrast and form, with their tallest flower stems and their leaves at their lush best. They also look especially striking as a seasonal boost among delicate plantings of diaphanous grasses or fountains of miscanthus and wispy verbena.
Cannas have enough presence to make effective contrast with bold buddleias and shrubs with coloured foliage, such as cotinus and physocarpus. They make a good background to roses, especially hybrid musks, which are often at their best in autumn, provided care is taken not to allow the roses to flail the foliage of the cannas.
While it may require a little extra effort to get the best out of cannas, they are not difficult to please and are hugely rewarding. They can be in bloom for six months of the year, and their foliage adds colour and excitement in gardens large and small, especially in autumn.