Tall with long, elegant stems surmounted by a ring of fine leaves (modified stems) which radiate out from a central hub, this sedge will grow a couple of metres tall, a stately presence above the surface of your pool or pot.
Smaller but equally valuable as a water margin plant and much easier to find in garden centres, is its relative, cyperus alternifolius. Sometimes known as the umbrella plant, it hails from Madagascar and has a circle of broader, grass-like leaves gracing the top of each slender stem.
Both are what Americans like to call “accent plants”, and provide a contrast to surface-hugging plants such as water-lilies, or floaters such as water lettuce or water hyacinths. I have a cyperus growing at the edge of my fish pond and a couple in large pots keeping company with guppies and Mexican swordtails which hide in its ample roots. And it will grow more-or-less anywhere.
Another familiar sight on Thai forecourts is the water canna or Thalia geniculata, an upright foliage plant, often with attractive red stems, and large bright green, lanceolate leaves which appear lower down the growth. The clusters of tiny flowers are purple with white spots and dangle from the ends of stalks which may be three metres tall. Settled in a well-watered pot, Thalia can take the full sun of a patio, but it will also survive in permanently moist soil, or at the edge of your fish pond where it will add height and substance to existing foliage. Thalia will germinate from seed or can be divided at the roots. An “accent plant” with a difference. Leaves tend to go yellow at the edges, particularly if short of water.
Both the papyrus and water canna root, conventionally enough, in saturated soil. On the other hand, the water hyacinth (eichornia crassipes) literally floats on water. So named because it produces lilac-hued spikes of hyacinth-like blooms above bulbous, air-filled stems, these blooms can look attractive in a confined space. The free-hanging submerged roots are purplish-black, the stiff oval leaves a deep green.
One of the fastest growing of plants, it reproduces by means of stolons or underwater runners which form new plants. Because of this rapid growth, it can colonise and dominate a stretch of water in days, carpeting the entire surface and killing off other aquatics. The water hyacinth also has some commercial value in Asia: it can be pressed into service as a mulch or fertiliser while its fibrous roots are used to make up-market, woven furniture. This needs to be exploited.
Eichornia is a bit more exotic than the humble water lettuce (pistia stratiotes) which also floats, but produces no flowers of any significance. In similar fashion, its emerald green, deeply pleated rosettes of leaves sprout from roots trailing below the surface. These lie more-or-less flat when there is plenty of surface room, but if the rosettes are close together in a pot, they will become more upright in habit. Pistia reproduces by means of offsets: these can be removed to start a new colony elsewhere.
If grown in garden ponds, both these “floaters” provide some shelter for fish, and the capacity to remove some impurities from the water. But they should not be allowed to cover the entire surface: they will need to be periodically culled, and to have their dead leaves removed – before they de-oxygenate the water.
The water chestnut (trapa bicornis) is probably a better choice for the small garden. Another “floater”, it looks neat with flat, diamond-shaped, leaves which form an attractive rosette above the submerged fruit. These hard brown fruit, which resemble the horned head of a bull – hence the botanical name – contain a large starchy nut considered a delicacy, especially among the Chinese. Submerged, these fruits can be used to propagate new plants. In the wild, the fine roots may extend for three or four metres, anchored in the mud at the bottom of a pond or slow-moving stream. Trapa is happy in strong sunlight and since it is less invasive than the water lettuce, it looks good in a container.
“The Tropic Gardener”, an indispensable guide to plants and their cultivation in Thailand. Available from the author at email@example.com, from Seng Ho bookshop in Phuket Town or Delish in Rawai.