Technology fact sheet
- Water hyacinth (Eichhornia crassipes), an invasive aquatic species, is used to build rafts for floating vegetable cultivation in flooded areas during the monsoon season.
- Farmers produce seedlings and vegetables on the rafts.
- The decomposing raft is used to increase the soil fertility of arable land during the winter season.
Water hyacinth contains elements needed for plant nutrition (N, P, K) at concentrations comparable to cow dung1.
- Crops mature faster on the rafts, making multiple crop cycles possible in one season.
- Creates additional cropping area.
This graph summarizes the results of a sustainability assessment conducted for this technology. The closer the line is to the outer edge of the diagram, the better the technology performs in terms of the particular criterion
What is a floating vegetable garden?
- Growing vegetables on floating beds is a traditional practice in the floodplains of coastal Bangladesh.
- A floating bed, constructed of water hyacinth and other aquatic plants, is used for production of high-value vegetables during the monsoon season, when much arable land is flooded.
- When the water recedes after the monsoon, the rafts are left to decompose on arable land, thereby adding to soil fertility for production during the winter season.
- The technology has many purposes: farmers gain ‘land’ for vegetable production during the monsoon flooding, the fertilizing qualities of water hyacinth are exploited in both the monsoon and winter season, and waterways are rid of water hyacinth.
- Floating beds can be used to produce vegetables (for family consumption, with the surplus being marketed) or seedlings (for sale or transplanting to homestead gardens).
- The vegetables produced include eggplant, bitter and wax gourds, pumpkin, cucumber, onions, taro, okra, amaranth and water spinach2.
- Because of the fertilizing properties of water hyacinth, crops mature faster on the floating garden beds. Thus, multiple crop cycles are possible in one season on one raft.
- No land is required. Bangladesh floating gardens offer a sustainable farming method in flooded and waterlogged areas, with economic, environmental and social benefits.
- Growing vegetables on floating beds is a traditional practice in the flood plains of coastal Bangladesh.
- Traditionally, farmers have used long-straw paddy stub to construct floating garden beds. As the improved rice varieties that are grown now, produce short straws which decompose rapidly, and long straws have household use, water hyacinth is used instead.
- In southern Bangladesh, floating cultivation is part of an organized value-chain, with farmers raising seedlings for sale.
- Floating garden cultivation was popularized in Bangladesh in the late 1990s by a well known national agricultural television programme.
- Since 2000, extension programmes have been disseminating information on floating garden vegetable cultivation to farmers in inland areas of Bangladesh3.
- Floating garden cultivation has been on the national agenda in Bangladesh since 2005 with the launch of the National Adaptation Programme of Action (NAPA) 2005 which was revised in 2009.
- In 2013, the Government of Bangladesh approved a $1.6 million project under the Bangladesh Climate Change Trust Fund to promote floating gardening as a climate change adaptation method. The three-year project is being implemented by the Government's agricultural extension wing in 40 subdistricts of 8 districts countrywide.
Where it works
- The technology is suitable for seasonal or perennial water bodies where climatic conditions allow vegetable production and where construction material for the rafts, like water hyacinth, is available free of cost.
- The water should be still or slow-moving (depth is unimportant).
- In perennial wetlands and permanently waterlogged areas, floating garden cultivation is possible all year long.
- Farmers in different areas use different materials4 and techniques to construct the rafts, depending on availability of the material, stagnancy of water, onset of monsoon, wetland area possessed by the farmers and the household financial situation.
- Materials needed to construct the raft are bamboo poles, organic matter such as aquatic and other plants and a tool (stick hook) to cut the plants.
- Rafts are usually constructed in the May–July period, depending on local conditions.
- The preparation of rafts depends on the availability and maturity of the hyacinth. Water hyacinth must be fully mature and this takes about 60 days. Rafts made from immature plants are not durable.
- Farmers usually gather the hyacinth and other plant material by themselves. However, due to increased demand, aquatic plants are sometimes purchased from local markets.
- The size of the raft varies, depending on the size of the water body, plant material and labour available. For the purpose of this document, a floating bed is assumed to be 15 x 2 x 1 m.
- The life cycle of a floating bed is six to eight months: three to six weeks of raft preparation, four months of floating and several months of decomposition.
Constructing the floating garden bed
- Place the bamboo poles to form a frame of the desired length and width on a mass of fully mature hyacinth. The plant mass and frame are then placed in shallow water for easier raft construction.
- Standing on the frame and using the stick hook, the farmer pulls the water hyacinth (or other aquatic plant used for the raft construction) from both sides of the frame, flattens it with the feet and weaves it into the raft5.
- This process is continued until the desired length and breadth is achieved and repeated until the right thickness of the raft is reached. This first layer acts as the base of the floating bed and maintains its stability, buoyancy and thickness. It is recommended that the height of the decomposed bed be at least 1 m above the water line. This requires several layers of water hyacinth.
- Once the raft's basic structure has been created, the bamboo poles can be pulled out.
- The raft is left to rest and decompose for one week.
- The newly constructed raft can be used for cultivation immediately if mulch, soil, compost or cow dung are spread thickly on it.
- If soil is not used (as described in the step above), more water hyacinth (or other aquatic plants) can be added to the top of the raft after seven days. The raft is left to decompose for another 15 to 30 days, depending on local conditions. When the top layer turns black, the raft is ready for vegetable production.
- The decomposing top layer of the raft should always be moist to facilitate the decomposition. Therefore, the raft should be watered if there is no rain during this period.
- If necessary, the raft is then hauled to the desired anchoring spot and can be tethered to bamboo poles.
- The raft should be placed in still water (water depth is unimportant). Water areas that are affected by tides or currents make the raft more vulnerable to erosion and disintegration.
- The vegetables on the floating bed should be protected from predators (especially rats and ducks) with a fence.