How to Grow Water chestnut

Eleocharis dulcis · Also called: Chinese water chestnut, Matai, Bi qi, Apulid, Haeo, Groundnut sedge

A dense stand of upright green tube-like water chestnut stems growing from shallow water.

Photo: Photo by David J. Stang, CC BY-SA 4.0 (Wikimedia Commons)

Water chestnut is grown for one property that almost nothing else in the vegetable world has: it stays crisp after it is cooked. Boil it, fry it, stew it or can it, and it is still crunchy at the end, because the walls of its cells are bound together in a way that heat does not break down. That single fact is why it appears in so much of Chinese and Southeast Asian cooking and why it is one of the few vegetables worth canning whole. China grows the great majority of it, with Thailand, Vietnam, the Philippines and Australia also producing. It is grown in flooded fields much like rice, and it suits ground that is too wet for almost anything else — which for a farmer with a low-lying, waterlogged corner is the real point.

Growing Water chestnut, Stage by Stage

1. Get the land ready and flood it — Puddled mud that holds water, exactly like a rice paddy.
2. Plant sprouted corms, which are this crop's planting material — Last year's crop is this year's seed.
3. Weed the paddy and hold the water — Hold the water and the weeds mostly look after themselves.
4. Wait for the corms to form, late in the season — Nothing happens underground until the days shorten.
5. Watch for trouble — Few pests, one health point, and one that lives in the water.
6. Drain the field and harvest the corms — The hardest work of the whole crop, all in the last week.
7. Store the corms whole, and sell what you can peel — Whole keeps for months. Peeled keeps for hours.

Common Problems & Troubleshooting

If you see: A magnificent tall green stand that produces almost no corms when the plot is dug.

It likely means: Usually too much nitrogen, or a season that was cut short. Corms only form late, as the days shorten, and nitrogen late in the season grows tops instead.

Do this: Stop feeding nitrogen well before the corms begin to form.

If you see: Harvest taking far longer than expected, with corms left behind in the mud.

It likely means: Heavy soil, or a plot drained too recently, or a single pass. Digging is the main cost of this crop and it is decided when you choose the field.

Do this: Choose a soft loam or silt over heavy clay when you can, since clay gives a good crop you cannot get out.

If you see: Stored corms gone wrinkled, light and woody within a few weeks.

It likely means: They were stored dry. These corms are mostly water and lose it fast in open air.

Do this: Store whole unpeeled corms cool and damp, in moist sand, sawdust or water.

If you see: A buyer who wanted water chestnuts rejecting your crop, or asking why it is not a horned nut.

It likely means: Two different plants share the English name. They wanted singhara, the water caltrop, which floats on open water and has a hard horned fruit.

Do this: Establish before planting which crop your buyer means, and agree it by its local name as well as in English.

If you see: Nothing at all on the crop, but concern about the water the field is flooded with.

It likely means: That concern is correct and worth acting on. Corms grown in water receiving human or animal waste can carry a parasite that infects people who eat them raw.

Do this: Use the cleanest water supply you can, and keep animals and latrines away from it.

If you see: A full crop of corms that are all small, however many there are.

It likely means: Usually plants set too close, or a short season, or water that was allowed to drop during corm formation.

Do this: Space the corms 50 to 75 centimetres apart each way, since each plant spreads a long way.

Yield & Market Value

Growing the crop is only part of the job. The last part is knowing what a normal harvest looks like where you are, and knowing what your water chestnuts are worth before you agree a price with anybody.

Remember It This Way

If you forget every other page of this guide, keep these lines. They are the whole crop, in order, short enough to carry in your head.

Grown like rice: bunded, puddled, flooded.
Planted from last year's corms, not from seed.
Sprout the corms first, then push them bud-up into the mud.
Wide spacing. Each plant runs a long way.
Hold the water all season. Never let it dry.
Stop the nitrogen before the corms start forming.
Nothing forms underground until the days shorten. Give it the full season.
Lift when the tops have browned, not before.
Drain, let the mud firm, then dig it twice.
Store whole and damp. Peel only what sells today.

Test Yourself: Identification

What does the growing crop look like?

What does the crop look like when it is dug?

What is it like inside?

Honest Limits of This Guide

Timings here are given by season and by the state of the crop rather than in named months, because water chestnut is grown in both hemispheres. Count from your own last frost.
The English name water chestnut covers at least two unrelated crops. This guide covers Eleocharis dulcis, the Chinese water chestnut, a rooted sedge. Singhara or water caltrop (Trapa natans) is a floating plant with a horned fruit and is not covered here.
The parasite risk described here is real and documented for aquatic crops grown in water receiving human or animal waste, and it is the reason the guide says to peel and to cook where there is doubt. It is a reason to be careful about water quality, not a reason to avoid the crop.
Labour is the dominant cost of this crop and is not something this guide can put a number on, because it depends entirely on your soil and your wages. Dig a small trial patch before committing a field.
There is no photograph here of a flooded field, of planting, or of the crop being dug out of the mud, because usable pictures of that work are not available under a licence this library can use.
The fourth picture is a botanical illustration, not a photograph. It is used because it shows the underground runners and the corms forming at their tips, and no usable photograph shows that.
No varieties are named here. Planting material is corms saved from the previous crop and passed between growers rather than bought as named varieties.
No chemical treatments are named here. The crop is eaten and often eaten raw, and what is permitted differs by country and by buyer.

Sources

GBIF Backbone Taxonomy species-match record for Eleocharis dulcis (Burm.f.) Trin. ex Hensch. — Global Biodiversity Information Facility (GBIF), Copenhagen (source)
EPPO Global Database — Eleocharis dulcis (EPPO code ELODU) — European and Mediterranean Plant Protection Organization (EPPO), Paris (source)
Eleocharis dulcis — CABI Compendium datasheet — CABI, Wallingford (source)
FAO guidance on growing crops in flooded and wetland fields — Food and Agriculture Organization of the United Nations (FAO), Rome (source)
FAO guidance on post-harvest handling and storage of root and corm crops — Food and Agriculture Organization of the United Nations (FAO), Rome (source)

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