Plants for gardening in water

I know I am far from alone in my belief that a garden is not complete without a body of water. Water has been valued as an element in the landscape since gardening began, providing a visual hub of tranquil serenity around which a garden naturally radiates.

And it is the rapport between water and the plants that grow in and around it that is the key to harmoniously blending land with water in the garden.

The true water plants or aquatics take on various forms. They can be soil-bound, with their foliage held above or on the water's surface and anchored by roots adapted to growing in waterlogged soil. There are surface floaters that have left the soil altogether, deriving their water and nutrients directly from the water alone.

Then there are the so-called 'oxygenating' plants that will flower on the surface but photosynthesize entirely or partially under water. Although they are seen to give off minute bubbles of oxygen, the role of these plants is often exaggerated, as the amount of oxygen they provide is insignificant.

The most effective oxygenation comes from any kind of water movement, such as that provided by streaming bubbles in an aquarium, a fountain or recirculating cascades. The bubbles are not somehow absorbed, instead the movement of water improves its ability to exchange gases and absorb oxygen, either from the surface or from oxygenating plants. These plants still play a useful role in helping achieve a natural ecological balance, while adding depth and detail to the water. Their underwater foliage offers protection to fish from birds and shelter for their eggs to be laid and hatched.

Fairy moss, Azolla caroliniana, is a deciduous perennial, floating fern that adds colour and texture to the water's surface. It is believed to help control algae by restricting the amount of light falling into water. Its colour varies according to the intensity of available light; from rich reds and purples in full sunlight to greens or blue-greens in the shade.

A number of aquatic and marginal plants add a bonus of food production to water gardening. For example, the sacred lotus, Nelumbo nucifera, is prized not lonly for its dazzling flowers and immense waxy, water-repellent leaves, but also for its roots, highly prized in Asian cooking.

The Chinese water chestnut, Eliocharis dulcis, adds a delicious, sweet, coconut- like flavour to stir-fried cooking or may be eaten raw. Planted over spring and summer in a sunny, protected, frost-free area, they take about seven months to mature. In one season under ideal conditions, each plant can produce as much as one kilogram of corms which store well in the refrigerator.

Although planting of aquatics is much easier before water is added or existing ponds drained for the purpose, it is still feasible to plant into existing bodies of water. Direct planting into the soil makes sense in dams or larger ponds, especially in rural areas where plants in pots can be vulnerable to disturbance from visiting wildfowl.

Cultivating plants in containers, however, allows them to be moved about as desired and eases access for maintenance or propagation. To minimize the leaching of nutrients and prevent the potting medium from washing away, the bases of pots should be lined with hessian, newspaper or fine mesh, and river sand or gravel applied to top of mix. Ledges or pockets to support containers should be included in the profile of a pond or dam as it is constructed.

When using pots for planting aquatics, any good standard-grade potting mix without added fertiliser or lime will suffice. Blood and bone and well-rotted cow manure are more effective than chemical fertilisers and slow release pellets which dissolve too rapidly under water.

Natural bodies of water rarely end abruptly, but are more likely to blend with solid land in a gradual transition. The soil in these margins progresses from being waterlogged and anaerobic to wet or moist, and many plants have evolved root systems enabling them to thrive in these varied conditions. Some, such as a number of irises, may be planted with their roots completely underwater, while others prefer to be sited in moist soil just above the water level.

Marginal plants help to blur the visual distinction between land and water. Many grasses or grass-like plants, such as poas, sedges, rushes, lilies and irises, are suited to these conditions, their vertical thrust counterpointing the horizontal planes of the water.

Other plants can be used as accents or focal points. A clump or two of Gunnera manicata, the giant rhubarb from Colombia and Brazil, makes a dramatic scultpural statement at the water's edge. Resembling a larger form of edible rhubarb, its tough, spiky and richly textured leaves are surmounted in early summer by huge conical flower spikes. It can tolerate a range of growing conditions from being fully submerged to normal garden beds.

The massed, hair-like foliage of Cyperus papyrus, Nile grass, was used by the Egyptians to make the first paper and its fine detail contrasts splendidly with tranquil water in the larger garden. It is a tall, spreading, evergreen perennial sedge with huge umbels of delicate flowers in summer. The rhizomes are edible, and the plant grows in moist, wet or totally submerged soil, in sun or part shade. C. haspan, a dwarf species very similar to C. papyrus, creates a similar effect on a smaller scale.

Equally striking for the smaller garden is C. alternifolius, umbrella grass, with its windmill-like rosettes of rib-like leaves held aloft on stems about a metre high. It thrives in shallow water or moist soils, in both sun or shade.

The areas surrounding existing dams or larger ponds can often provide scope for marginal plantings or bog gardening. A difficult garden area can sometimes be exploited by growing plants which will thrive rather than trying to laboriously correct a drainage problem. Alternatively, a bog garden can be designed into the perimeter of a new pond by allowing a portion of liner to extend over a shallower 'pond' which is filled with soil rather than water.

In larger bodies of water, tussocks or small islands can be created by building mounds of soil which project above the water level, contained with chicken wire to prevent them washing away. Clumps of grasses, lilies or irises can then be planted into the tussocks, creating a varied wetland environment.

A pond or dam introduces the gardener to a vast new palette of diverse plants, only a few of which I have been able to mention here. Specialist water garden nurseries can offer many more colours, shapes and forms.

Selected aquatic plants

Aponogeton distachyus, water hawthorn, cape pondweed. Normally deciduous, deep-water plant with distinctive oblong leaves floating on the water surface. Very fragrant white flowers are produced from winter to summer.

Cotula coronopifolia, brass buttons, water buttons. Short-lived marginal plant to 30 cm, with button-like yellow flower heads throughout the year except late winter, above lance-shaped leaves on fleshy stems.

Hydrocleys nymphoides (syn. Limnocharis humboldtii), water poppy. Frost tender, deciduous deep-water aquatic plant, evergreen in warmer climates, with floating, oval-shaped, mid-green leaves, and poppy-like, yellow flowers held above water surface.

Marsilea drummondii, common nardoo, and the larger M. mutica, are terrestrial or aquatic evergreen native ferns which grow from rhizomes. Attractive clover-like fronds float on the water supported by stalks about a metre long. M. quadrifolia, water clover, is a more compact exotic relative.

Myriophyllum aquaticum (syn. M. brasiliense), parrot's feather or diamond milfoil is one of the so-called oxygenating plants with a dense, delicate filigree of bright green foliage which provides protection for fish eggs.

Nymphaea spp. water lilies. These are not discussed in this article as a detailed article on the subject appeared in the same issue of The Australian Gardener.

Nymphoides aquatica, fairy water lily or banana plant. White flowers.

N. indica, water snowflake. Lily-shaped leaves and clusters of flowers 20­80 mm tall. White flowers with yellow or orange stamen.

N. peltata, yellow floating heart or water fringe is a floating plant for shallower water, 15­45 cm deep, which can become invasive. Its rounded, bright green leaves resemble those of a miniature water lily. Dainty yellow flowers are held about 50 mm above the water surface.

Noxious water plants

Some of the plants listed here are still available through Australian waterplant specialists, and were originally introduced as ornamental water plants. Their invasive nature has resulted in their declaration as noxious weeds in some Australian states where their cultivation is illegal.

Alternanthera philoxeroides, alligator weed (NSW, NT, Qld, SA, Vic)
Eichhornia spp., water hyacinth (NSW, NT, Qld, SA, Tas, Vic, WA)
Elodea canadensis, water weed, pondweed or ditchmoss (NT, SA, Tas, WA)
Lagarosiphon spp., curly water thyme (NSW, NT, Qld, SA, Tas, Vic, WA)
Myriophyllum aquaticum (syn. M. brasiliense), parrot's feather (Tas, WA)
Pistia stratiotes, water lettuce (NSW, NT, Qld, Tas, WA)
Sagittaria graminea (SA, Tas, WA)
Salvinia spp. (NSW, NT, Qld, SA, Vic, WA

Specialist waterplant suppliers in Australia

Austral Watergardens, 1295 Pacific Highway, Cowan, NSW 2081.
Dragonfly Aquatics, Forrest, Vic. 3236. (03) 5236 6320. A wide range of aquatic plants available by mail order.
Everglades Watergarden Supplies, 216 Abbotts Road, Bootawa, NSW. 2430
www.everglades.com.au (02) 6553 0700, Fax (02) 6553 0744
L.R. & N.R. Gedye Pty Ltd, 37­41 Elizabeth Street, Doncaster East, Vic. 3109. 1800 036 102. Waterlilies, iris and other waterplants; pond equipment including punmps, fibreglass cascades and pools.
Ledora Watergardens, 851 Pacific Highway, Mt Kuring-gai, NSW 2080. (02) 9456 1163.
Lotus Watergardens, Gardenworld, 810­834 Springvale Road, Keysborough, Vic. 3173. (03) 9798 4599, (03) 9701 6038.