Nymphaea, Water lily

Water lilies are the ultimate pond plant, giving beautiful shapes and exquisite colours, from white and blues to pinks and reds. The flowers of some, such as 'Indiana', even change colour as they age, such as from orange-yellow to rich bronze-red.

Most of the hardy varieties were bred by the French nurseryman Mnsr Latour-Marliac, who began producing some outstanding hybrids in the late 1800s. The multi-petalled 'Gloire du Temple-sur-Lot' commemorates his nursery at Temple-sur-Lot, near Bordeaux, in south-west France. The prefix 'Marliacea' is used to signify a hardy variety of a high standard.

Recommended varieties

Choose a plant with plenty of young leaves, rather than flowers, for more vigorous, free-flowering results. Note that a pond should have at least two-thirds water to one-third plant cover to avoid a strangled appearance and ensure lots of reflections.

For large ponds,

N. 'Alba': this British native is too vigorous for all but the largest ponds. It will spread rapidly to create a glorious display of flowers and foliage.

For medium size and small ponds,

N. 'Gonnere': sparing but eye-catching, large, double white flowers.
N. 'Marliacea Chromatella': has well-shaped flowers over a long period and flourishes in smaller ponds.
N. 'Marliacea Rosea': a compact grower with intense pink, fragrant blooms among purple-green leaves.
N. 'Pink Sensation': a strong-growing variety with attractive green or purple-tinted leaves that may be flecked deep red. The cupped, gleaming pink flowers are large and striking, and appear over a long season.
N. odora var. minor: ideal for planting in a small, formal pond, or even an aquatic-tub or half-barrel. Its gleaming white, scented flowers, enhanced with conspicuous yellow stamens, appear over a long season, from late May - in a warm, sunny position - to mid-autumn.
N. 'Vésuve': developed by the French breeder Marliac during the 18th century, this free-flowering variety has a long season with scented red flowers which gradually get darker. Allow for a spread of 1.2m (4ft).

Tender blue

N. 'Director George T. Moore': a true blue, but it is tender. As yet, there's no hardy true blue.

Growing tips

Site preferences

All water lilies need a sunny spot to flower well, and will only open their flowers fully when the Sun is shining. Since they grow naturally in still water, avoid fountains etc. The best time to plant is from April to September, when most garden suppliers sell them in small pots. They need to be repotted before being immersed in the pond.

Aftercare

Varieties differ in their planting depth requirements, from 15cm to 1.2m (6in to 4ft) deep. Introduce plants to the correct depth over a few years, especially if the species is a deeper dweller. Do this by initially placing the potted basket on some bricks in the pond (take care if the pond has a rubber lining - a couple of spades of gravel beneath the bricks should protect it). Also, cover the soil surface with a layer of clean gravel to prevent water from washing it out. In large ponds, water lilies can be planted directly in the mud at the bottom. Once established, the plant will need little maintenance beyond the removal of old leaves in the autumn.

Small lilies growing in shallow water that's likely to freeze may need protection in winter. Provide an insulating cover on cold nights.

Flowering

Plants may take a while to settle in before flowering. Planting too deep is the most common reason for prolonged non-flowering. Remove flowers during the first year to allow the plant to establish and settle into its new environment. After that, you don't need to remove dying flowers as they soon get hidden from view (the blooms last about three to five days and, as they fade, the stems start to twist and coil, pulling the closed flower underwater).

Feeding

Feed twice a year with fertiliser tablets made specially for water lilies. Push them into the soil at the base of the plant.

Placing a water lily in a basket

The traditional container is a plastic mesh basket, lined with hessian or sacking and filled with good-quality soil. The newer louvre baskets have very fine slits instead of hessian.

Place good-quality garden loam or aquatic compost in the bottom, and check for depth.
The water lily should be planted with its growing point at soil level. Firm in the soil.
Finish off with a thin layer of gravel over the surface to prevent the soil from washing out.

Dividing

Water lilies need dividing every five years or so, by which time they usually have leaves rising above the water surface, obscuring the flowers. Lift the whole plant in the spring and wash off all the soil. Use a sharp knife to detach a piece of rhizome with a vigorous growing point, and pot up separately. This can then replace the old plant.

Pests and diseases

Water lilies are fairly trouble-free. However, they may suffer a few pests and diseases. These are mostly superficial and will do little permanent harm to the plants.

Be wary of using chemical controls if you have fish in the pond. If aphids attack the leaves and flowers, blast them off with a hose. The fish like to eat them.

The China-mark moth can be a nuisance during summer by laying eggs near the edge of leaves. These hatch into larvae that cut oblong-shaped pieces of the lily pads, which they use to surround their body. They continue to nibble away while inside this protective coat, and eventually consume large chunks of foliage. The leaf-mining midge shreds the foliage, but is less common. Both pests can be picked off badly affected leaves. Fish also help to reduce their numbers.

Crown rot is the most serious disease. Leaves turn red, curl up and go crispy. Young plants are worst hit. The only method of control is to dig up the plant and soak it in a bucket of fungicide. After treatment, wash the plant thoroughly before returning it to the pond.