What should you know before growing a water chestnut plant? The edible water chestnut plant is Eleocharis dulcis, a rush-like sedge grown in flooded soil for its crisp corms. UF/IFAS says it needs about 220 frost-free days and 4–6 in (10–15 cm) of standing water. Do not confuse it with Trapa natans, an invasive plant New York regulates.
Key takeaway: Two different plants share the water chestnut name. The Chinese water chestnut plant (Eleocharis dulcis) is a tall sedge whose corms are eaten in Chinese cooking. Trapa natans is a floating Eurasian annual that forms dense mats and is invasive in the US. Grow only the sedge, in a watertight container or controlled pond.
| Feature | Chinese water chestnut | Trapa natans |
|---|---|---|
| Plant type | Rush-like sedge, tubular stems | Floating annual, leaf rosettes |
| Height or length | 3–5 ft (0.9–1.5 m) tall (UF/IFAS) | Stems 12–15 ft (3.7–4.6 m) long (NYSDEC) |
| Edible part | Corm 1–2 in (2.5–5 cm) wide | Not a garden crop |
| Spread | Rhizomes and corms | Floating rosettes and barbed fruits |
| Status | Food crop | Invasive aquatic plant |
Which Water Chestnut Plant Is Edible?
The edible one is the Chinese water chestnut, Eleocharis dulcis. UF/IFAS describes it as a rush-like plant grown in ponds for round corms whose chestnut-brown skin and crisp white flesh give it the name. A 1988 Florida State Horticultural Society paper says it is so named to distinguish it from the aggressively weedy Trapa natans.
Other names for this water chestnut plant, per UF/IFAS, include waternut, horse’s hoof and matai. The Florida paper says the sedge is native to eastern Asia and has an ancient history of cultivation in ponds in China.
Why Should You Avoid Trapa Natans?
It is invasive. NYSDEC says this Eurasian and African annual was introduced to the US in the mid-1800s as an ornamental and now forms dense mats that shade out native plants. Decomposing mats can lower dissolved oxygen and sometimes kill fish, and its sharp, barbed fruits cause painful wounds when stepped on.
NYSDEC reports it in more than 40 New York counties. Each rosette can produce up to 20 hard seeds, and seeds within fruits can stay viable for up to 12 years. For other plants that need containment, see our water hyacinth guide.
What Does a Water Chestnut Plant Need to Grow?
A water chestnut plant needs a long warm season and controlled water. UF/IFAS says an annual crop needs controlled irrigation, a growing period of 220 frost-free days, and about 4–6 in (10–15 cm) of water kept over the soil surface. The Florida paper adds that it does not grow well in acid or very sandy soil.
- Soil: the Florida paper cites muck or rich clay at pH 6.9–7.3, though sandy loam harvests more easily.
- Water: keep a shallow, steady depth; long dry spells may cause crop failure.
- Season: 220 frost-free days, so cooler regions start corms indoors.
How Do You Plant Water Chestnut Corms?
Start each water chestnut plant from firm corms. UF/IFAS says to set corms 4–5 in (10–13 cm) deep and 30 in (76 cm) apart, flood the plot for a day, then let it drain to settle the soil. When plants reach 12 in (30 cm), flood again for the rest of the season.
- Start corms in moist soil indoors if your season is short.
- Plant them 4–5 in (10–13 cm) deep and 30 in (76 cm) apart.
- Flood for one day, then let the water drain.
- Reflood once plants are 12 in (30 cm) tall.
- Keep 4–6 in (10–15 cm) of water over the soil.
The Florida paper notes seed is not practical because it germinates slowly and poorly and needs two years to reach normal corm size, so growers use corms or transplants.
Can You Grow a Water Chestnut Plant in a Container?
Yes. The Florida paper says home gardeners can grow Chinese water chestnuts in any watertight container, and small plastic children’s pools serve the purpose well. It estimates a home grower might harvest up to 20 lb (9 kg) of corms from about 11 sq ft (1 square meter) of planted area. A container also keeps the water chestnut plant contained.
- Give each water chestnut plant heavy soil with standing water above it.
- Feed lightly; see our fertilizer for plants in water guide.
- Compare another tub crop in our lotus plant container guide.
When Do You Harvest Water Chestnuts?
Harvest a water chestnut plant after the tops brown. UF/IFAS says corms reach edible size in late fall and water should be drained about 30 days before harvest. The Florida paper says flowering and corm development happen in early fall, and corms form 6–10 in (15–25 cm) deep at rhizome tips, so dig carefully.
Corms sprout if soil rises above 55°F (13°C), the Florida paper notes, so in temperate climates harvest and refrigerate them at 50–55°F (10–13°C) until planting. In warm climates they can stay in the ground as a perennial crop.
Where Does a Water Chestnut Plant Fit in a Water Garden?
Treat the water chestnut plant as a contained crop. UF/IFAS reports Gainesville trials in plastic-lined ponds filled with sand gave fair results but were labor-intensive. For ornamental ponds, compare options in our koi pond plants guide or grow edibles beside fish with pond aquaponics.
Is the water chestnut plant invasive?
The edible sedge is a crop; Trapa natans is the invasive one NYSDEC regulates.
How tall does a water chestnut plant grow?
UF/IFAS says its tubular stems reach 3–5 ft (0.9–1.5 m).
How deep should water be for a water chestnut plant?
UF/IFAS advises about 4–6 in (10–15 cm) over the soil.
Can I grow a water chestnut plant from seed?
Not practically; seed is slow, poor to germinate and takes two years.
How do I store corms over winter?
Refrigerate at 50–55°F (10–13°C), as the Florida paper advises.
Sources
- University of Florida IFAS Extension. HS683: Waterchestnut, Eleocharis dulcis.
- Morton, Sanchez and Snyder, Florida State Horticultural Society. Chinese Waterchestnuts in Florida: Past, Present, and Future.
- New York State Department of Environmental Conservation. Water Chestnut.
- Photo credits (Wikimedia Commons, edited with titles): Eleocharis dulcis Blanco1.15 by Francisco Manuel Blanco (O.S.A.) (Public domain); RIBogorSeerose by Ziegler175 (CC BY-SA 4.0); Pond-edge plants at Achamore Garden – geograph.org.uk – 5446824 by M J Richardson (CC BY-SA 2.0); Deep Cut Gardens Koi Pond by FossilDS (CC0)