Source: Permaculture Research Institute https://permaculturenews.org/2008/11/29/water-chestnuts/
The Water Chestnut, Eleocharis dulcis, is a tropical/sub-tropical sedge that grows in water margins and bogs in many parts of India, South-East Asia, New Guinea, Northern Australia and Polynesia. It is an annual that has erect, narrow, tubular leaves (clums) half a metre to a metre tall. The plant spreads by a creeping rhizome which, through the summer months, produces additional sucker plants. The sweet corms are highly valued as a nutritious food. They are also used medicinally for a number of ailments, used either fresh, boiled or steeped in rice wine. The corms contain an antibiotic principle called ‘puchin’, which acts like penicillin, helping in immune functioning. The stems may be used for mulch, fodder, fruit and vegetable packaging, and crafts.
Some varieties are not sweet and are grown for starch or pig feed. The Australian variety is small but quite sweet. Chinese varieties are superior in size and sweetness. Nick Romanowski of ‘Dragonfly Aquatics’ (a mail order aquaculture plant supplier) recommends the “Hon Matai” Chinese variety he has selected for its productivity and large size of corms, whilst it grows well even in cooler climates. Related Australian varieties, Eleocharis acita and E. Sphacelata, commonly called Spike Rush, are widespread, have taller stems, up to 1.5m, which provide good bird shelter and the corms are a favourite food of water birds, who may also nibble off the chestnut stems.
In Asia the water chestnut is grown in flooded fields, often in rotation with paddy (rice). Seed tubers are first raised in wet nursery beds then transplanted to the field, flooded, then left. Six months later the field is drained and the tubers harvested, with yields in excess of 7 tonnes/hectare. Twenty to fifty tonnes/ha have also been recorded.
Water chestnuts prefer to be grown in rich, sandy, well-limed soil 5-20 cm deep, with plenty of well composted manure or other organic matter added a few weeks before planting. Since water chestnuts are harvested by hand to avoid damaging the fragile skin, it is important to have soil as free of hard debris as possible (stones, woody plant material, etc).
Experiments in the USA indicate that the major nutrients taken up by a crop which yielded 4700kg/ha were nitrogen 108kg/h, magnesium 37.5 kg/h and calcium 6.9kg/h. The uptake of phosphorus and potassium was relatively low. Natural organic liquid fertilizers, such as seaweed extract, are suitable for use. The ideal pH range is between 6 and 7.5, so use dolomite (a form of lime that contains magnesium to adjust pH where necessary. Acid soils can lead to fungal problems in the stems, the only known diseases affecting them.
Growth & Harvest
Three corms per 2m2 can be planted in early spring, kept well watered and the stems allowed to reach 20cm high before flooding them to approximately 7-10cm depth (maximum 30cm). This level is maintained for the whole growing season of 7 frost free months (light frost won’t kill them however). A greater depth of water is tolerated by the plants but they do not prosper. Water is drained off prior to harvesting to expose corms and assist harvest.
One corm, under favourable conditions can typically spread to become 1m2 of plants, yielding approximately 3 kgs. In autumn the leaves start to yellow and this is when the rhizome form chestnuts or ‘corms’ at their terminal ends. Over a period of a few weeks the leaves turn brown and die back totally; the corms also develop a dark brown colour. The chestnuts can be harvested from this time onwards through winter until spring temperatures start them shooting again. The largest size that can be expected of corms is about 45mm in diameter.
Containers and Ponds
Water chestnuts are easy to grow in any container that holds water, such as an old bathtub or styrofoam vegetable box. They can be grown in a plastic lined trench (above ground, or dug in), or in large plant pots that are submerged in a pond. Chestnuts can also be grown in floating rafts on ponds.
Water chestnuts are a common ingredient in many Asian dishes, appreciated as much for their crisp texture as their delicate sweet coconut-like flavour. After cooking they retain most of their crispness which is even retained when left-overs are reheated. The chestnuts should be first washed and peeled. They can be eaten raw either straight or, as in Indonesia, blended into a drink. Thin, raw slices can be added to salads (even fruit salads) or clear soups. They need only brief boiling or frying (as in a stir fry), can be added to any stew or curry, be used as stuffing for poultry, made into flour, used as thickener, or minced and made into puddings, pickled in vinegar, or crystallized in sugar or honey as a sweet. With carbohydrate levels at 30% and protein 1.5%, they are a nutritious food source.