Water chestnuts have been considered as a potential crop in Western Australia for some years, but there are problems with developing this crop as it needs a specialised growing system and the market potential is uncertain.
The Chinese water chestnut (Eleocharis dulcis) is a sedge (Cyperaceae family) which grows in water. The plant is rush-like with upright tubular stems 1 to 1.5 metres tall. It produces numerous mahogany brown corms which resemble gladioli. These are sweet and crisp with a white flesh and nutty taste.
The Chinese water chestnut may be mistaken for the European type (Trapa natans) and another Chinese water chestnut (Trapa bicornis) which have dense floating leaves and produce a horn-shaped nut. These are not economically important and can become weeds.
To avoid confusion, the Chinese water chestnut is often referred to by its Cantonese name of ‘matai’ which means ‘horses hoof’. The variety grown in Western Australia is ‘Hon Matai’, which is the main commercial variety in the United States.
Water chestnuts are an essential ingredient in certain Chinese dishes such as ‘dim sims’, soups, desserts, puddings and stir-fried mixtures, but can also be used raw and in drinks. Until 1993, this delicacy was only available in cans in Western Australia.
During canning, the medicinal tonic or antibiotic called ‘puchine’ is destroyed, but fresh corms remain crisp and retain ‘puchine’ after cooking. For this reason, Chinese people regard fresh water chestnuts as superior to the canned product. The flavour has been described as a blend between apple, chestnut and coconut.
Water chestnuts are high in sugars (2.5%) and also contain about 18% starch, 4.7% protein and less than 1% fibre.
Problems with the crop
Chinese water chestnuts are a potential crop for specialised markets in warm temperate regions. However, they can only be grown in limited areas where specific water requirements can be provided.
They need to be completely submerged with a controlled level of water for most of the life of the crop (similar to paddy rice) and it is preferable to drain the water for harvesting.
Purchase of tanks or construction of dams is expensive, but a suitable channel can be made with a 50 by 4 metre plastic liner. The cost of planting material is also high and it is necessary to bulk up supplies of planting material before commercial crops can be marketed.
A major problem is that the corms present poorly for marketing. As many as 100 corms may be produced from each planted corm, but these may be too small (under 25cm in diameter) and attract low prices. It is estimated that a return of over $15/kg is needed to return a profit, because of the specialist crop needs.
Water chestnuts may also be grown in hydroponics using buckets and a suitable media such as perlite plus vermiculite. The buckets can be kept topped up with old nutrient solution from other crops.