During the flooding season, Luong Van Tran hires a large number of workers to harvest 500 kilograms of water caltrops daily in marshes in Dong Thap Province.  

The workers paddle down the marshes in Long Hung Commune, Lap Vo District, to collect mature water caltrops. Districts such as Lap Vo, Cao Lanh and Tam Nong in Dong Thap Province have grown this plant for years.

Water caltrop is a floating aquatic plant often grown in ponds and has an edible part called the corm. The corm grows underwater until it ripens and falls off into the muddy waters. Since the part develops and rests underwater until it is retrieved, it is technically considered a tuber rather than a fruit. 

In Dong Thap, farmers primarily plant the ‘buffalo horn’ variety, which has a rough texture and conical form as its name suggests.

Tubers from the water caltrop plant are harvested once every quarter or so. Each plant yields five to seven tubers, and is replaced with fresh saplings after three harvests to ensure high productivity.

Though harvesting the tubers seems fairly simple, the farmers must move in a single file to ensure a thorough harvest and saplings grow well.

To qualify as mature and ready for harvest, the tubers must be a deep beetroot color and the size of two human fingers. On average, a person can harvest 100 kg of water caltrop tubers a day.

Following the harvesting, the tubers undergo a brief washing and packaging process right in the marsh. 

Mai, 40, a worker, said: "For most part of the year I work on land, but during the harvest season I paddle down into the water. Each household employs a few workers to collect the water caltrop from 6 a.m. to 1 p.m. and pays VND120,000 ($5.2) a person per day." 

Sacks of water caltrops are directly bought at the site by merchants for VND5,000-7,000 ($0.2-0.3) per kilogram. During the main harvest season, Tran (left) reaps 300-500 kg of water caltrops. "My annual income is VND50 million ($2,170)."

After nearly three decades in the business, Tran currently has 10,000 square meters of marsh to grow water caltrops. "While the harvest season used to be solely during the last quarter of the year, we now harvest throughout the year. Regardless, water caltrop tubers are of prime quality during the flooding season from July to October."

Water caltrop tubers are rich in carbohydrates and fiber, making it a nutritious food. When boiled, it has a sweet, nutty taste, making it easy to incorporate it into a variety of dishes such as hotpot and sweet soup.

This tuber also boasts a wide range of health benefits from curing gastritis to treating sunstroke.