Cultivated since ancient times, Eleocharis dulcis is a perennial aquatic plant popularly known as Chinese water chestnut. This iconic vegetable belongs to the large Cyperaceae family, which is dominated by sedges such as papyrus and cotton-grass.
E. dulcis has leafless tubular stems, but its foliage is not what imparts economic importance to the plant. Underneath the surface, and sheathed by mud, form delicious root crops called “corms”. Contrary to what the common name suggests, the corms of this plant aren’t actually a type of nut. Rather, they are specialized vegetables used for nutrient storage.
Originating in Southeast Asia, water chestnut is now found as far as northern Australia and tropical Africa. It thrives in aquatic environments, such as marshes and swamps, and has deep green stems which jut through the surface of the water. These leafless stems produce tiny inflorescences at their tips, after which corms begin to develop in the muddy substrate.
The corms grow up to 5 cm in diameter and are found at the end of horizontally spreading rhizomes attached to the base of the plant. Due to their black-brown appearance and papery skin, the Chinese refer to them as ma tai (Cantonese for “horse’s hoof”).
Water Chestnut Growth, Hardiness & Climate
Given the right conditions, water chestnut should be a relatively easy plant to care for. With a preference for tropical climates, it will require at least 7 months of warm weather to properly mature. In China, these are grown in paddies that are thoroughly irrigated at the beginning of a growing season. Their affinity for growing in waterlogged soil makes them a wonderful option for filling in the borders of a pond or water garden. They can even be grown in a bucket of soil, so long as the roots of the plant remain submerged in water. Corms begin to develop under photoperiods of 12 hours per day, so keep your plant in a sunny area if you’d like to partake in its vegetables at the end of the season.
Generally, the rushes of this plant are unsusceptible to diseases if grown in neutral to slightly alkaline soil. Acidic soil may cause the plant to develop stem blight, a fungal disease that is characterized by dark-colored, watery lesions. Water chestnut may also attract pests such as grasshoppers, weevils, and mole crickets, though these are not known to have particularly devastating effects on the plant.
How to Plant Water Chestnut
Water chestnut does not produce seeds and is instead grown using its corms. To plant the corms effectively, you would first need to select a proper container for the soil. A large drum, deep plastic tub, or bucket would do the trick depending on how many corms you wish to plant. Fill the tub or container with approximately 8 inches (20 cm) of organic potting mix. If you wish to use soil from your garden, make sure that its pH is at least 6.5. For every square footage of soil, you will need no more than two corms, as these tend to propagate quickly. Plant them into your soil (at a depth of at least 2 inches) in early spring, and ensure that they are spaced out so that the seedlings don’t get overcrowded.
Once you’ve covered the corms and patted down the soil, you will need to fill the container with around 4 inches (10 cm) of room temperature water. For the duration of the growth period, regularly check the water depth and refill the container if any water has evaporated.
How to Care For Water Chestnut
Water chestnut is not a demanding plant and is relatively easy to care for as long as its minimum needs are met. Make sure the plant is situated in an area that receives full sun. Regularly check the water depth and remove any green moss or algae that can form on the surface of the water. Inspect the leaves for pests and disease and remove any dead or decaying plant parts. About 7 months after the planting date, observe the leaves for any changes in color. Yellowing leaves indicate that the corms are almost ready for harvest.
If you wish to harvest your corms, remove the standing water and let the plant sit in wet soil for about a month, or until the shoots become dry. Sort through the top 4 inches of the soil by hand, so as not to damage any corms, and gather any which you wish to harvest.
If you are located within zones 9 – 12, you may leave any corms that you do not wish to harvest in the container or pond set-up. Regularly remove dead leaves, and wait until they begin to shoot up again in spring. If located outside of these zones, harvest all of the corms if you cannot take the container indoors. The corms can be refrigerated and kept in a dark cool place prior to replanting next spring.
How to Winter Water Chestnut
This rush-like perennial is frost-tender and will have to be transferred indoors or fully harvested before the first frost. Collect your harvested corms and gently wash them to remove leftover soil. Store the cleaned corms at 4˚C (39˚F) in a dark area. Do not let them dry out on a kitchen shelf or outdoors as they will not survive being frozen. To prevent rot, ensure that they are not exposed to excessive moisture. Replant the corms in the spring, when the final frosts have thawed.
Is Water Chestnut Invasive or Toxic?
Eleocharis dulcis is not considered an invasive plant. Unfortunately, it is often confused with the European water chestnut (Trapa natans), which is invasive in North America. Luckily, it is easy to differentiate between the two species because their leaves are quite different. The Chinese variety has long grass-like leaves, whereas the invasive European species produces feathery green leaves that form rosettes.
Although water chestnut is not toxic, it is associated with Fasciolopsciasis when eaten uncooked. This infection is caused by an intestinal fluke and normally results in mild symptoms.
Where to Buy Water Chestnut & Seeds? (UK & US)
Eleocharis dulcis corms and juvenile plants can be purchased from plant nurseries, aquascaping shops, or via online plant portals. Fresh corms can even be purchased in outdoor markets and organic produce groceries throughout their native range. When purchasing this species, do keep in mind that it is often confused with the invasive European variety. As a rule of thumb, pay attention to the scientific name when purchasing this plant, and bear in mind that it may have special requirements for growth outside hardiness zones 9-12.
