Water chestnut

Water chestnut: how do you recognise it?

Habit

Annual floating plant with a rosette about 60 cm across on the water surface, anchored to the bottom by a long submerged stem.

Leaves

Diamond-shaped, toothed floating leaves in a rosette; the leaf stalks are swollen and filled with air.

Flowers

Small white flowers with four petals, among the leaves, in July–August.

Fruit

A hard, dark nut with two to four sharp horns; it ripens in autumn and sinks to the bottom.

Life cycle

Annual: every spring a new plant grows from a nut, and the plant dies in autumn.

Flowering: July–August · Harvest and fruit: September–October · Plants: May–June

Why grow it?

• A striking rosette of diamond-shaped, toothed leaves that decorates the water surface.
• An unusual annual for water-plant lovers: every spring a new plant grows from a nut.
• The floating leaves give shade and shelter to fish and tadpoles.
• The nuts are edible and have long been eaten.
• The nuts with their sharp horns are a real curiosity, fun for children to discover too.

Water chestnut: where does it grow best?

• Full sun: it needs a warm summer to grow and form nuts.
• Still, warm, nutrient-rich water; no current, fountain or waterfall.
• A water depth of about 50–100 cm is enough; the stem adapts its length.
• Acid to neutral water, preferably with a muddy or loamy bottom.
• Allow 60 cm per rosette: it can form dense mats, so leave room for other plants.

Light

Sun

Soil type

Loam, clay or peat

Acidity

Acid or neutral

Moisture

Wet

Size

0.05 m tall, 0.6 m wide

Hardiness

Hardy (to -15 °C)

Goes well with

• Water lily: Another floating plant that also needs warmth and sun; plant it some distance away.
• Frogbit: Small, round floating leaves and white flowers among the rosettes.
• Hornwort: An underwater oxygenating plant and shelter for young fish.
• Flowering rush: Pink umbels in summer in the marginal zone.

Water chestnut: when and how to plant it?

Plant in May–June.

1. Put the nuts or young plants in the pond only in May–June, when the water has warmed up well.
2. If you have nuts, keep them in a tub of water in a warm, bright place until they germinate. They must always stay under water.
3. Let the germinated nut sink to a muddy or loamy bottom, or put the young plant in a basket of loam covered with a layer of gravel.
4. Choose a spot 50–100 cm deep with plenty of sun and no current.
5. Let the rosettes float freely: the stem grows up to the water surface.

Care

Water

Keep the pond topped up. Replace evaporation with rainwater.

Feeding

Not needed: the water in an ordinary pond is nutrient-rich enough.

Thinning

In a dense mat, remove rosettes in summer so that other water plants get light.

Harvesting nuts

In September–October, collect the ripe nuts if you want to keep them. Wear gloves: the horns are sharp.

Storing nuts

Always keep them wet, in a bucket of water in a cool, frost-free place. They must not dry out.

Tip: If you want new plants every year, let a few nuts sink to the bottom in autumn or keep them in a bucket of water in a cool, frost-free place. Dried nuts are useless.

Water chestnut: when to prune it?

When: It is not pruned: it is an annual. In summer you remove rosettes that are too dense, and in autumn you clear the dead plants.

How:

• From June to August, remove excess rosettes by hand or with a net.
• In October, skim dead plants from the water.
• If you want to keep nuts, collect them before clearing the plants.

Caution: Wear gloves when harvesting and clearing: the nuts have sharp horns.

Pruning calendar and basic rules

Propagation

Storing nuts

In September–October, collect fresh nuts and keep them under water all winter in a bucket, in a cool, frost-free place. Dried nuts no longer germinate.

Germinating

In April–May, put the nuts in a tub of warm water in a bright place. After a few weeks a stem with a rosette appears; put it in the pond in May–June.

Water chestnut: how does it get through the winter?

Hardy to −15 °C: protect young plants.

• The plant is an annual and dies in autumn; the nuts overwinter under water on the bottom.
• Water under ice stays close to 0 °C, so the nuts on the bottom survive ordinary Belgian winters, even in frost down to about −15 °C.
• If a small pond or tub could freeze to the bottom, keep the nuts in a bucket of water in a cool, frost-free place.

Diseases and pests

• No germination: The nuts have dried out or the water is too cold. Always keep them wet and let them germinate in warm water.
• Duckweed and blanket weed: They take light away from young rosettes. Skim them off regularly.
• Aphids: On the floating leaves in summer. Wash them off with a jet of water; fish and ladybirds help.
• Slow growth: In a cool summer it grows poorly and forms few nuts. Choose a sunny, sheltered spot where the water warms up quickly.

Through the year

• March: Check the overwintered nuts and refresh the water.
• April: Germinate the nuts in a warm, bright tub.
• May: Put the germinated plants or nuts in the pond.
• June: Plant. Follow the growth. Skim off duckweed.
• July: Flowering begins. Top up the water.
• August: Flowering. The nuts ripen. Remove excess rosettes.
• September: The nuts ripen and sink. Harvest with gloves.
• October: Skim dead plants from the water. Keep nuts under water.
• November: Resting. The nuts lie under water.
• December: Resting.

Edible and useful

Nuts (September–October)

Water chestnuts ripen in September and October, mainly after a warm summer in pond water that warms up well; in a cool summer there are few. Ripe nuts are dark and hard and come away easily: carefully lift a rosette and pick them from under the leaves, or scoop sunken nuts from the bottom with a net. Always wear sturdy gloves, as the horns are razor-sharp. Inside the hard shell is a white, starchy kernel that, once cooked, is reminiscent of sweet chestnut, mild and slightly sweet. Only eat them thoroughly boiled, then fried or roasted if you like, never raw. This is not the tinned water chestnut of Chinese cooking. Keep a few nuts in a bucket of water every year: the plant is an annual, and without nuts there will be no water chestnut next year.

Storing

Fresh nuts keep for a few days in a bucket of cold water; cook them as soon as you can. Cooked, shelled kernels keep for 2 days covered in the fridge, or up to 3 months in the freezer. Always keep nuts for sowing wet, in a bucket of water in a cool, frost-free place: once dried out, they no longer germinate.

Caution: Never eat water chestnuts raw: as with other water plants, they can carry larvae of parasites, such as liver fluke, and germs from the water. Always boil them in their shells for at least 30 minutes, even if you fry or roast them afterwards. Only harvest from your own pond, and only if the water is clean: not from water fed by manure or waste water, or where sheep or cattle drink. In the wild, the water chestnut has disappeared from our region or become very rare, and it is protected in many European countries: never harvest it in the wild, and never release it into a ditch or other open water. The horns stay sharp even after cooking: wear gloves and do not leave the shells lying where children, dogs or cats could step on them.

Eating and using is at your own risk: see the terms of use.

Recipes

• Boiled water chestnuts (Dish · 2 to 4 people · 1 hr)
• Brussels sprouts with water chestnuts and bacon (Dish · 4 people · 30 min (with cooked water chestnuts))

Did you know?

• The swollen leaf stalks are filled with air tissue and work like a float ring for the rosette.
• Remains of the nuts have been found at prehistoric sites in Europe: people have been eating them for a very long time.
• Despite the name, it is not related to the Chinese water chestnut of the kitchen (Eleocharis dulcis, a sedge).