Shrimp heads sweeten the watermelon: 30 years of sandy-soil circular farming on Co To Island

On Co To (Cô Tô), a remote island in Quang Ninh Province in northern Vietnam, one family has spent 30 years on a method that turns shrimp heads into compost and returns it to watermelon fields on the coastal sand. Reported on July 3, 2026 by Nong Nghiep va Moi Truong, a trade paper affiliated with Vietnam's Ministry of Agriculture and Environment, the story describes how tourists visiting the island drop by the field, experience growing and harvesting, and buy on the spot. Processing by-products from seafood, maintaining fertility on sandy soil, and drawing in tourists: challenges that Japan's remote islands and coastal producers each carry separately, this small field solves together in a single cycle. It is news to read not as a commodity to procure but as a "model you can take home."

Watermelon grown on shrimp heads: 30 years in the Hai Tien hamlet of Co To Island

The central figure is Do Thi Quyen, a farmer in the Hai Tien hamlet of Co To Island. Her family has grown watermelon on the island since 1997, nearly 30 years now. This year's planting is about 2 mau (a customary northern Vietnamese unit, roughly 0.7 hectares), with an expected yield of about 4 tonnes, the article reports.

The field is sandy coastal soil. Quyen says "soil improvement is the most important step of all," and places the composting of shrimp heads at its core. The family buys shrimp heads from seafood processing plants on the island, lets them decompose, and works them into the field as organic fertilizer. Once decomposed, the shrimp heads become a mineral-rich layer of nutrients that softens and enriches the sandy soil and allows the use of chemical fertilizer to be held down, the article explains.

The Co To watermelon grown this way is described as not large in size but intensely sweet, with red, firm, moisture-rich flesh. The island's environment of sea breeze and strong sunlight seems to reinforce this character.

Why "shrimp" for an island watermelon: a nutrient cycle closed within the region

The weak spot of island farming is the cost of inputs. Fertilizer and materials all cost more by the shipload, and on the same footing as the big producing regions of the mainland there is no winning a price war. Co To, meanwhile, is an island of fishing and seafood processing, where shrimp heads and shells are a resource that arises daily on the "hard to dispose of" side.

The value of Quyen's method lies in connecting these two directly. It cuts the chemical fertilizer bought from off the island and turns what was being thrown away on the island into nutrients for the field. The article frames this as an effort that turns waste into a resource, holds down environmental load, and moves toward a circular, sustainable green agriculture.

Sandy soil with poor nutrient retention is, by nature, disadvantaged for high yields. The idea of building up fertility by adding organic matter is far from flashy, but its 30-year run is proof above all else.

The field became a tourist spot: how locals see it

The local reactions that can be gleaned from the article are all practical.

• Quyen herself says that for cultivation on sandy soil the soil-improvement step matters most of all, and places the composting of shrimp heads at the core of her success.
• In recent years tourists visiting the island have come all the way to Quyen's farm, walked through the green farm space, observed the growing and harvesting steps, and tasted and bought the freshly picked produce on the spot, the article reports.
• The paper rates this effort as a model of circular farming that turns seafood by-products, a form of waste, into a resource and curbs environmental pollution.

The family does not rely on watermelon alone; it grows gourds and sweet potatoes in parallel. The stance of spreading across crops to keep both the field working and visitors entertained also leans toward a tourism-farm style of operation.

Implications for Japan's island farming and tourism farms

Seafood by-products can become a "fertilizer that can be sourced on the island"

On Japan's remote islands and in towns with fishing ports too, seafood processing residue is a nuisance that carries disposal costs. On the other side, farmland is troubled by stubbornly high fertilizer prices. Materials derived from crustacean shells have a track record of use in soil improvement in Japan as well, and the condition for reproducing this scheme is less technical novelty than the sheer closeness of "the processing plant and the field being in the same hamlet." The legal rules for waste handling and the design of hygiene management are prerequisites, but the idea of circulating nutrients within an island works best for remote producing areas that struggle with transport costs.

The "story of the cycle" itself becomes a tourism product

Japan's tourism farms rely mainly on harvest experiences, but what draws tourists to the Co To field, on top of the fun of picking, is the tellable mechanism that "shrimp heads grow the watermelon." Showing the field itself becomes sales promotion and supports the unit price of direct sales. This case shows the order: rather than adding experience menus, it is faster to first polish one story about your own field.

A design that works even at about 0.7 hectares and 4 tonnes

A scale of about 2 mau planted and roughly 4 tonnes expected is about the same level as a Japanese family-run field. It works nonetheless because it ties the "demand that comes to you" of the tourists visiting the island to direct sales and steps off the price-competition track. Earn with unit price and story, not by expanding scale. This overlaps with the order that small producers in hilly, mountainous, and island areas should take.

The Vietnamese producer context: the "sea and farm" combination is advancing

On Co To Island, a shift from catching wild squid to farming it a 210-hectare marine aquaculture plan is also underway. As sea production becomes planned, processing increases, and as processing increases, by-products increase too. For shrimp as well, a three-stage high-tech farming operation in Thanh Hoa Province and other intensification is advancing in various places, so shells and heads, the "raw material of the cycle," are set to build up rather than shrink going forward.

Moves to turn small areas at high unit prices are also springing up simultaneously across Vietnam. A case in Ha Tinh Province turning three melon crops a year on 500 square meters Like it, the Co To watermelon is a "design-not-area" model. From a Japanese buyer's standpoint, the Co To watermelon itself is for island consumption and tourism, not an export commodity. The business opportunity lies rather in the opposite direction: a sell-in of small composting equipment and materials and know-how for processing by-products, brought into the production areas of Vietnam.

Practical information and next actions

To bring this case home to your own situation, you can start with the following three.

1. Island and coastal municipalities and farm cooperatives should take stock of what by-products local seafood processing plants generate and in what quantity, and match them against the soil-building demand on the field side.
2. Tourism farms, before adding experience items, should polish "why this field is delicious" into a single story of a cycle, and place it on the flow line of tours and direct sales.
3. If you are arranging a tour of Vietnamese production areas, add not only large plants but family-run circular models like Co To to the itinerary, and confirm the smallest unit you can take home to your own area.

Sources

• Ngot lanh dua hau Co To (Co To's sweet watermelon) - Nong Nghiep va Moi Truong, July 3, 2026