SCIENTIFIC NAME: Eleocharis dulcis
FAMILY: Cyperaceae

The water chestnut (Ma Taai) is a reed that produces an edible bulb in winter. Though not a tree, this is the type of alternative crop that many tree croppers have shown an interest in as it promises a good short-term income while their other trees become established. Water chestnuts belong to the sedge family. Both leaves and stems are erect, like rushes, in tubular clumps of green quills. Water chestnuts are not, of course, true nuts; they are edible roots with a distinctly nutty flavour, especially when freshly gathered. The chestnuts themselves form in the mud at the base of the stem.

Three years ago this crop was almost unknown in New Zealand, but quiet work by enthusiastic amateurs has caused sufficient to be available for commercial cropping to begin within the next season. Two factors have added to the commercial viability of this plant. The first is the influx of new Asian residents who cannot import the fresh product. The second is the loss of the suitable growing land in China, as much of the Guanzhou province of southern China transformed into a modernised business development zone, which should see China become a net importer of the nut within three years. Thailand and the Philippines will still be large exporters but only New Zealand and Australia have the advantage of seasonal difference, allowing overseas markets the fresh product year around.

There are a number of different ways in which water chestnuts can be grown.

In ponds. The traditional Chinese technique is to grow them in the mud of a shallow pond. However, this method is being strongly discouraged by New Zealand environmentalists because of the danger of our wetlands being invaded by escapees. This will threaten native New Zealand vegetation, and in particular a rare native sedge of the same genus, sometimes called the "Maori Chestnut".

In containers. They can be grown in containers. Practically any shallow container will do, such as old water troughs, old tubs, drums or plastic containers. Garden soil can be used, and if it is a bit clayey, so much the better. Or use a standard potting mix, but not one that is mixed with peat moss or manure. About 100 mm is enough, covered with about 50 mm of water. As a variation, cut-down plastic containers can be placed in a larger container of water, such as an old paddling pool. The smaller containers can be removed individually to make harvesting a little easier. A 100-litre container is said to produce about thirty to forty mature chestnuts; smaller containers will produce proportionately fewer. Water chestnuts mature in about six months but can be gathered much sooner if your growing season is not that long or if you will settle for smaller 'nuts'. In climates where roots would freeze under water, they must be stored over the winter. Remove the roots from the water (in their containers) and store in a cool, moist, shady place. The pots should be laid on their sides. Check every so often to be sure the soil has not dried out.

Under plastic. Growing on plastic slashes the harvesting costs. The beds are laid out in August on any flat land (mulch film is good enough). Five cm of soil is covered with 10 cm of water, and the nuts or plants are set out at 70 cm spacing. A clear plastic cover provides heat in the early months, and by May the plants die down, forming 10 to 50 nuts per 70 cm square of plastic. The root mass is simply rolled back to reveal the nuts hanging underneath.

Ken Franklin, who grows his under plastic, says, "My own beds last year cost $100 per square metre to produce $1000 worth of product, but only a small proportion was sold (to other growers). When it all settles down, the cost will be more like $1 per square metre with a return of only $15. This is still a very good return for a small patch of dirt considering that the only work required during the growing season was the replacement of water lost through evapo-transpiration. An umbrella company has recently been formed to coordinate bulk purchase supplies, and marketing."

Cross-section of a bed of water chestnuts.

Using Chinese Water Chestnuts

Almost anyone who has ever eaten or prepared Chinese food knows about water chestnuts. In many countries, supermarkets stock them canned and packed in water, and people who prepare their own Chinese dishes frequently buy a can because the recipe calls for them, However, they are less available in New Zealand, and, unfortunately, canned water chestnuts are only a pale version of the real thing as both crispness and flavour suffer in the canning process, When fully mature, they are about the size of a walnut, although the canned ones are usually smaller. If you grow your own, store for about three weeks after harvest to dry out. Fresh water chestnuts are covered with a tough brown skin which should be peeled before eating. Once peeled, store them in water in the refrigerator because the white flesh will discolour quickly if left exposed to air. If you need to keep them more than a day, change the water every twenty-four hours.

Culinary Uses
Water chestnuts are prized for two characteristics: their nutty flavour and their crispness. Fresh, their flavour resembles that of fresh coconut. They can be eaten both raw and cooked, but, if cooked, should be added toward the end of preparation so that they do not lose their crispness. They should be peeled before using. Like most Chinese recipes, cooking time once the vegetables are prepared is about six minutes.

Salads. Slice water chestnuts thinly and add them to a tossed salad along with radishes and cucumbers. This makes one of the best salads ever.

Stir fries. A good stir-fry vegetarian dish combines sliced water chestnuts with mushrooms, bamboo shoots, snow peas, bean sprouts, spring onions, and taro root. All the ingredients should be either sliced or cut into small pieces so that they can cook quickly - the whole dish won't take more than five minutes, including the gravy made with stock, soy sauce, and cornstarch. If you like a hotter version, add a chilli pepper and some grated fresh ginger. For meat eaters, shredded chicken or pork can be cooked first and then the vegetables added.

Soup. A clear soup garnished with a few thin slices of water chestnut becomes an authentic beginning to a Chinese meal - although it would do just as well as a starter for roast beef dinner.

Sauces. If you like creamed vegetables, combine water chestnuts and celery in cream sauce. A popular Chinese dish with a sweet-and-sour sauce (rice vinegar and sugar) includes water chestnuts along with bell peppers, celery, bamboo shoots, and Chinese cabbage.

Stuffing. Water chestnuts are also a good ingredient to include in eggroll stuffing because they stay crisp even if you make the egg rolls ahead of time and freeze them for later use.

Chestnut flour. In China, water-chestnut flour is a valued cooking ingredient, but I don't think you will grow enough of your own chestnuts to use them this way.

(Ref. Geri Harrington - Grow Your Own Chinese Vegetables.)

Adapted from an article by Ken Franklin in the Waikato Branch Newsletter.
Reprinted from The Tree Cropper, Issue 8, June 1996

DATE: September 1996

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