- Type
- Tubers & Storage Roots
- Difficulty
- Moderate
- Season
- Spring·Fall
- Sowing
- From bulb
Water Chestnut (Olbanggae)
Eleocharis kuroguwai
Starch · a tub-grown famine tuber
Olbanggae (Eleocharis kuroguwai) is a Korean native spikerush, a different species from the Chinese water chestnut (Eleocharis dulcis) that the English name usually points to, so material written about one does not transfer to the other. It is a perennial aquatic sedge that forms small black tubers, about chestnut-sized, at the tips of its runners. What looks like upright foliage is in fact hollow stem; the edible part is the tuber buried in the mud below the waterline. In paddy fields it is one of the hardest weeds to control, but in the city a few plants are grown in a water tub or a large pot kept flooded. Anything grown in standing water is cooked through before eating, and the skin is taken off with a knife, never with the teeth. The Donguibogam lists 烏芋 in its vegetable section under the Korean name olmoe, describing it as slightly cold in nature, bitter and sweet in taste, and free of toxicity — though one account calls it toxic. The same entry records that it was dug and eaten in the first and second lunar months, and gathered in quantity as a food stock in famine years. Its description of arrowhead-shaped leaves, however, does not fit olbanggae, which has no leaves, so opinion is divided over whether 烏芋 refers to this plant.
Year-Round Calendar
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Where It Grows
- Wild population Common in rice paddies and along waterways. What is grown as water chestnut in southern China, however, is nambanggae (Eleocharis dulcis), a different species.
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Wild population
Distributed in rice paddies, ponds and ditches from the central region of the country southwards. Harvest November, December, January
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- Wild population Known there as kuroguwai, it comes up in rice paddies; what is grown for eating is generally a separately selected cultivated strain.
It is a perennial water plant of East Asian rice paddies and waterside ground, ranging across Korea, China, Japan and Taiwan. What is sold as water chestnut in English-speaking countries is usually the closely related nambanggae (Eleocharis dulcis), grown in southern China and Southeast Asia, so the two species need to be read apart. Olbanggae itself is treated in many places as a weed to be controlled in paddies, so there are no production figures for it by country.
- Optimum
- 20~30℃
- Range
- 10~35℃
- Hardiness
- Hardy
It grows where water stands — rice paddies, ponds and ditches. Summer heat makes it spread quickly, and in midsummer a single day of dried-out water will lay the stems flat. In winter the stems wither, but the tubers survive unfrozen in the soil and come up again the following year.
In Korea Central Korea and south
Common in rice paddies, ponds and ditches from the central region southwards. The tubers are buried in a flooded tub in spring and dug from November onwards, once the stems have withered. Because it becomes a weed that is hard to control once it gets into a paddy, it is grown only in a sealed-bottom water basin.
How to grow
- Light
- At least 6 hours of direct sun. Good light is what fattens the tubers
- Soil and depth
- Lay 15cm or more of paddy soil or potting mix in the base of the tub, then flood it. Sand alone is too lean
- Spacing
- Three or four tubers in a 40cm tub. Crowded plants give small tubers
- Watering
- Keep 5-10cm of standing water over the soil at all times. In midsummer a single dry day flattens the stems
- Feeding
- Bury slow-release fertiliser in the soil at planting. Scattered on the water it feeds algae instead
- Harvest
- From November, once the stems have browned off, drain the tub and dig through the soil for the tubers. They can also be left in the mud through winter and lifted as needed
What makes the difference. Plant tubers 3-5cm deep with the bud facing up, then fill the tub slowly. Pouring water in all at once floats the soil
Why this one is harder. It spreads with real force — one tuber can become dozens in a single season, and once it reaches a paddy field it becomes a weed that is very hard to control. Grow it only in a sealed tub or pot, and never let the water or soil run off into a stream, a paddy, or a storm drain. When clearing up, dry the soil out and bag it as household waste
Common problems
- Mosquito larvae You will see Small larvae wriggling up and down at the water surface and along the walls What to do Change the water weekly, or add a killifish or loach or two. Do not keep other standing-water containers beside the tub
- Aphids You will see Clusters on the stem tips standing above the water What to do Wash them off with a jet of water. Use no chemical sprays, so nothing mixes into the growing water
- Snails and apple snails You will see Stem bases grazed and softened, with cut stems floating on the surface What to do Pick them off by hand at night. Never introduce apple snails to the tub deliberately
This page describes how a crop is grown and used. It does not claim health effects for any food, nor is it intended to prevent or treat disease. Component and study notes are references only and do not mean the same result occurs in people. Consult a medical professional about health concerns.
Health Benefits
The Donguibogam record — the 烏芋 entry and a reservation about identification. The Donguibogam entry for 烏芋 in the vegetable section carries the Korean names olmoe and gacharagi. It is described as slightly cold — cold, by another account — bitter and sweet in taste, with two records set side by side: free of toxicity, and toxic. The text says it grows in wet ground everywhere and belongs to the same group as water plantain, and that its root is yellow, like a taro but smaller, and fit to eat once boiled through. It records digging and eating it in the first and second lunar months, gathering it in quantity as a food stock in famine years, and preserves the alternative names 鳧茨 and 葧臍. The same entry, however, likens the leaves to arrowheads, which does not fit olbanggae — a plant with no leaves at all, only upright hollow stems — so opinion is divided over whether 烏芋 refers to olbanggae. This is an old medical record and differs from modern medical judgement.
Tissue firmness after heating — nambanggae. In analyses of the related nambanggae, or Chinese water chestnut, ferulic acid cross-linking in the cell wall was reported to keep the tissue from softening readily after heating. It is the standard account of why the texture stays crisp once cooked. This concerns tissue structure and composition, and has no bearing on preventing or treating any illness.
Nutrition
- Starch (the bulk of the tuber's dry weight) — storage carbohydrate, historically milled into flour
- Dietary fibre (spread through skin and flesh) — cell-wall material behind the texture
- Potassium (in the tuber) — a mineral commonly measured in tuber vegetables
Starch, once milled into flour The tuber is mostly starch. Grated and settled in water, it leaves a white sediment that was dried and worked into jelly cakes and rice cakes. The old note that the root was dug for food and gathered in quantity during famine years follows from the same property.
Crunch that survives cooking In the related nambanggae — Chinese water chestnut — analyses have reported that ferulic acid cross-links in the cell wall keep the tissue from softening readily under heat. This is the usual explanation for why water chestnut stays crisp in a stir-fry. Native olbanggae also keeps some bite after boiling, but the analysis above was carried out on nambanggae. Read the two species separately.
Preparing and cooking — never raw The tuber is high in water and contains potassium, a composition typical of vegetables eaten for their storage organs, like potato and taro. Scrub the dug tubers under running water. The layer just under the skin is the firmest and carries an earthy note, so peel generously with a knife — never with the teeth. Peeled tubers brown quickly, so hold them in cold water, and because the plant grows in standing water, cook the tubers through rather than slicing them raw into a salad or blending them into a drink.
Pairings
○ Stir-fries — Peel, cut into thick slices, and cook over high heat. The bite survives cooking, so it holds its texture among softer vegetables. The longer it fries, the more its sweetness comes forward.
○ Rice and porridge — Dice it into rice before cooking, or stir it into porridge. The high starch content thickens a broth as it breaks down. This matches the Donguibogam note about milling it into flour.
○ Meatballs and dumpling filling — Finely chopped, it gives the filling something to bite on. It holds a lot of water, so squeeze the chopped tuber once before mixing. Adjust the salt at the end.
△ Tubers grown in water — never eaten raw — The surfaces of fruits and tubers from freshwater plants grown in paddies, ponds and ditches are documented as a route by which parasite cysts such as Fasciolopsis buski are passed on. So scrub harvested olbanggae under running water, take the skin off with a knife rather than the teeth, and cook the tuber through. Do not slice it raw into a salad or blend it into a drink, and do not hand it to a child raw.
Varieties
- Olbanggae (native form) (tuber) — Native to Korean paddies and wetlands. Small tubers with black skin
- Nambanggae (tuber) — The relative eaten as water chestnut in China and Southeast Asia. Much larger tubers
Source: Donguibogam, Vegetable Section, 烏芋 · Rural Development Administration (Nongsaro)