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The Garden
July 2004
Sirens singing out
Flamboyantly exotic, the gorgeous blooms of tropical waterlilies can be enjoyed in these climes with a little coaxing. Phil Clayton falls under their spell.
Images: Tim Sandall
You may think you know waterlilies. The pristine, almost virginal, chalice-shaped white flowers of our native Nymphaea alba float quietly on the surface of calm waters amid rounded green pads, gracing many pools and slow-flowing rivers in summer. There are several hardy species and cultivars with flowers of soft yellow, pale pink and muted red, and all have a distinctly feminine beauty, bringing an impression of purity and serenity to the water garden.
But there are waterlilies and waterlilies. Despite their undoubted charms, hardy species and their cultivars represent only half the story. From the world’s warmer regions - Africa, Asia, South America and Australia - come tender but spectacularly seductive species and selections with attributes that make their hardy cousins look distinctly tepid. By comparison, tropical waterlilies seem almost indecent, their beguiling blooms in saturated colours siren calls to lure the unwary close to the water’s edge. The popularity of the subtropical look has drawn a few adventurous gardeners to experiment with these and their relatives in the UK climate, and they are becoming more, if not yet readily, available.
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Tropical waterlilies are available in hues unheard of among the hardy species and hybrids, despite attempts by breeders. Cultivars such Nymphaea ‘Albert Greenberg’ which has flowers in so-called ‘sunset colours’ (mixtures of orange, yellow red and pink) is a good example and popular in the USA |
Confused relations
The waterlily family Nymphaeaceae contains six genera. In addition to Nymphaea (waterlily) and Nuphar (brandy bottle), the hardy selections of which are familiar to UK growers, Victoria (giant waterlilies) are grown as ornamental plants in subtropical and tropical climes. Tropical Nymphaea are often confused with Nelumbo, as both are commonly called lotus, but that genus belongs to its own family Nelumbonacaea. Nelumbo nucifera is the true sacred lotus of India and the flower in which Hindus believe Buddha was born, while Nymphaea caerulea, the Nile’s ‘blue lotus’, was a symbolic plant to the ancient Egyptians and often depicted in tomb wall-paintings and architecture. The tubers of both plants were also important historically as sources of food.
Tropical versus hardy
In North America, tropical lilies are extremely popular, even in states such as Colorado, where winters are far colder than in the UK. They are widely grown, often in containers on patios as well as in ponds, and easy and cheap to obtain, many growers treating them as annuals. The critical factor for success with these plants is water temperature, and British summers are usually shorter and cooler than those of the USA. With the aid of a pool or aquarium heater and a good summer however, there is no reason why adventurous UK growers cannot enjoy tropical lilies outdoors, and in a glasshouse or conservatory, success is almost certain. The problem for most potential growers is simply obtaining plants: few UK nurseries sell them, and as stock is limited, plants may be costly.
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A remarkable range of flower colours is epitomised by the following cultivars of tropical Nymphaea: (click on name for a close-up) Top row: ‘Golden West’, ‘Green Smoke’, un-named seedling Second row: ‘Director George T Moore’, ‘White Delight', ‘Saint Louis Gold’ Third row: ‘Albert Greenberg’, ‘Tina’, ‘Mrs Martin E. Randig’ Bottom row: ‘Golden Fascinator’, ‘Jack Wood’, ‘Blue Horizon’ Styling: Alexandra Baulkwill; plants courtesy of Dorset Water Lilies |
Apart from requiring warmer conditions, tropical waterlilies differ from their hardy relations in several respects. They come in dark purples, mauves, azure blue, sky blue, rich reds, shocking pinks, bright yellows, oranges, the so-called ‘sunset’ colours (shades of orange mixed with yellow and pink) and even green, all of remarkable intensity, as well as more subtle pastel shades and white. Many also have attractive leaves or ‘pads’, often toothed at the edges and splashed with purple. The undersides may also be purplish and, while leaf colouring is usually most intense when pads are young, some cultivars such as mauve-flowered Nymphaea ‘Leopardess’ retain their attractive mottling.
One delightful characteristic of the ‘tropicals’, as they are often referred to, is that their flowers are held well above the water surface on stout petioles (flower stems), unlike the water-level flowers of the ‘hardies’. This probably an adaptation to the typically rapidly-fluctuating water levels in tropical rivers.
Many also have particularly sweet, heady fragrances that carry on the air and add to their allure. They fall into two groups: day flowering and night flowering. Night flowerers open their blooms at dusk, closing around noon the following day, usually with flowers of white, pink or red. Their pungent fragrances attract night-flying pollinators.
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The exquisite beauty of a typical tropical waterlily flower, rising high above the water, is typified by Nymphaea ‘Blue Horizon’ |
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Tropicals also differ from the more familiar hardy waterlilies in that they grow from small tubers rather than from large creeping rhizomes. The tubers are easily started into growth in warm conditions |
Tropicals are usually supplied in spring as small, blackish tubers about the size and shape of a walnut. These should be placed into water-filled, transparent plastic bags floated in a small fish tank placed by a sunny windowsill and heated to about 27°C (81°F). Shoots and leaves will appear quickly and develop roots. These can be severed from the tubers and placed into small (9cm/3.5in) pots of loam for growing on; the tuber will sprout again and can then also be potted up. Sink the pots onto the base of the tank, and once plants are established, reduce the water temperature for a few weeks to about 23°C (73°F). This encourages the growth of resting leaves (underwater leaves) that help to build up tubers.
Once plants are growing well and have produced floating leaves, they can be repotted into larger pots and placed in their growing positions. Many need only about 50 - 60cm (20 - 24in) depth of water so thrive in large watertight tubs. If possible, grow on in a glasshouse with the water kept to about 24°C (75°F) with an aquarium heater. Around the end of May (depending on the weather), move the container outside to the warmest, sunniest spot possible. Black containers absorb heat more readily than paler ones. Ideally, position the tub near an external power point so a heater can be plugged in should temperatures fall, but in a good summer plants should not need this back-up heat.
If you have a sheltered pond in a sunny spot, the lily can go straight out from June onwards. In a cooler pond, grow the lily in a black watertight tub plunged into the pond with the top of the tub 20cm (8in) above the surface; the water in the smaller tub will be warmer and kept insulated. In cold areas or in poor summers it may be better to keep plants in tubs in the glasshouse for the entire season. Conservatory gardeners may consider adding a heated pool for the ultimate after-dinner talking point (especially if planted up with headily-scented night-blooming lilies).
Tropical waterlilies are heavy feeders. At the Royal Botanic Gardens, Kew, ‘feed balls’ of one part blood, fish and bone to three parts loam are formed with a little water, rolled into snooker-ball-sized pellets and dried. These are pushed into lily pots weekly.
Once growing away, tropicals are generally free of problems. The most troublesome pests are water snails that munch holes in leaves. Algae may hamper the growth of young plants, but can be removed by hand. As plants develop, shade from the spreading pads will reduce light levels, making algae less of a problem.
Flowering performance
Providing water temperatures stay high enough, tropical waterlilies produce a succession of their glorious blooms. Each flower opens and closes for about four days before fading, changing subtly in the process. When they first open, the anthers are tightly packed in the centre of the flower and the petal colour is at its most intense. Only at this stage is the stigma of the flower receptive to pollen. The flowers close at night (or during the day if the plant is night flowering), to reopen with the anthers opening outwards and shedding pollen. The flower colour fades slightly until, by the end of the fourth day, it has become pale and the stamens are laid flat against the petals.
These waterlilies set seed easily; after the flowers have withered, the peduncles coil up or spread outwards, pulling the developing seed under the water, to where it can germinate and take root.
Some tropical lilies are viviparous, producing plantlets with roots on the leaves of established plants that can be detached and planted up. Viviparous tropicals are the most cold tolerant and are generally easier to keep going in less-than-ideal climates.
Overwintering
Perhaps the trickiest part of growing tropical waterlilies is overwintering them. Even in a heated conservatory there is little point keeping them growing over winter in the UK as there is too little light for flowering.
Falling water temperatures at the end of summer induce plants to ‘tuber up’. By the end of September, growth can be cut away and tubers retained. Clean them off and place in a jam jar of water in a spare refrigerator kept at about 14°C (57°F). Alternatively, store in moist sand in a cool room or glasshouse. Some may rot off, but others should survive.
Phil Clayton is Assistant Features Editor for The Garden
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