When I first heard about Hügelkultur, I thought it was the most extraordinary method of growing vegetables I had ever come across, although a useful idea if your problem is not enough depth of soil.  But as I recently scanned idly through many a screen, my eye was caught by a reference to floating vegetable gardens. It brought back a very vague memory of my first-year university studies. Fifty-five years ago, when I was doing my degree in prehistory, we had to start by looking at an overview of the prehistory and (some of) the history of the whole world. I remembered hearing about the floating vegetable gardens of the Aztecs, a useful idea if your problem is growing food for a city surrounded by water.

The Aztec empire flourished in central Mexico during the 14^th, 15^th and early 16^th centuries CE. Their capital city was Tenochtitlan, built on islands in Lake Texcoco, now the site of Mexico City.  They were a warlike people, but their science, art and architecture were also impressive; they had a written language, and an interesting if somewhat bloodthirsty belief system. The Aztecs kept track of the year using two separate calendars, one for ritual and one for agricultural purposes, which together formed a 52-year cycle. The Central American civilizations did not use wheels except for spindle whorls and children’s’ toys. They had neither potter’s wheels nor wheeled vehicles, perhaps because of the terrain or the lack of suitable draft animals.  They also didn’t have guns, so their sophisticated society was brought to an end by the arrival of foreign invaders, the Spanish Conquistadors, who did.

The Aztecs were migrants to the Valley of Mexico from the north. When they arrived there in the early 14^th century the area was already inhabited. Their capital was built on a small island in a swamp because this site was uninhabited and easily defended.  As the population grew, the chinampas were their solution to providing the city with food. Chinampas were not really floating gardens. They were artificial islands, created by building wattle fences on the lake bed to create small square enclosures which were then filled in with dredged-up lake mud, brush and waterweeds from the surrounding waterways, all rich in organic material. Trees, especially willows, were planted around the edges of the islets to increase stability, and the surrounding waterways were kept clear, allowing canoes to pass among the gardens, and maintaining a constant supply of water to the gardens. The fertile soil thus produced was extremely productive.  The Aztec farmers grew, among other vegetables and herbs, maize, beans, squash, tomatoes, chilli peppers and amaranth (a plant which produces tiny nutritious seeds which can be used like cereal grains). 

Chinampas did not compete very well with modern industrial methods of farming and global trade, and gradually almost ceased cultivation. They recently became important again in supplying Mexico City with fresh food during the Covid-19 pandemic in 2020. Suddenly markets were closed, borders were closed and supply chains all over the world were disrupted. Surviving chinampas became the best source of fresh vegetables for the population of Mexico City (now 20 million people). They have been suggested as a good example of sustainable agriculture. And the chinampas of Xochimilco, south of Mexico City, are today recognized as a UNESCO World Heritage Site.  

The term ‘floating vegetable garden’ is often used rather loosely to signify a vegetable plot, man-made or otherwise, surrounded by water. The chinampas are not actually floating. The island of Madeira is sometimes referred to as a ‘floating garden’ because of its lush vegetation. In France, the Hortillonages are a labyrinth of tiny islets accessible only by a network of canals, which once supplied the town of Amiens with fruit and vegetables.  However, there are parts of the world today where vegetables are actually grown on floating constructions made of locally-available plant material.

In the Indian sub-continent, there are farmers who cultivate vegetable gardens that are free-floating. The practice was traditional in Bangladesh in areas which are often flooded for long periods during the monsoon. The long thin vegetable beds are constructed on a base of water hyacinth stems, bamboo, and rice stalks, beaten into mats and covered with silt, chopped water hyacinth, manure, and soil. The beds are anchored in place with bamboo poles but can rise and fall with changing water levels. The vegetables best suited to these floating gardens, which are usually around half a metre thick, are shallow-rooted leafy greens such as spinach, amaranth, beans, okra, tomatoes, aubergines, chillies, gourds, and herbs such as mint, ginger and coriander.  They can be up to 55m long, although shorter lengths are commoner; usually 10 – 15m long by 1m wide. Unlike the chinampas, they last for months rather than centuries, and need to be rebuilt every flood season.

The beds are cheap and easy to build, very fertile, and as they gradually decompose, produce excellent compost. They are considered to increase food security in areas prone to disastrous floods, and also something which gives status and economic benefits to women, who often do the cultivation. Furthermore, water hyacinth* is a highly invasive species from South America, which needs to be cleared from waterways anyway, as it interferes with fishing and water transport and allows mosquitos to breed, so this is an added benefit.  Bangladesh is very low-lying and is likely to be seriously affected by climate change and rising sea-levels, so floating vegetable gardens may become even more useful in the future.

Floating vegetable gardens are also used in parts of India, such as Dal Lake. Dal Lake is a large shallow freshwater lake in the city of Srinagar, Kashmir, in India. The lake is a noted tourist attraction, with a beautiful setting in the Himalayas, lined with gardens, parks and boulevards, and dotted with houseboats. Its floating vegetable gardens supply the city with fresh food. Reeds and bulrushes are woven together to make large mats which are dried out for several years before being covered with a layer of mud and planted with vegetables. These gardens can be moved around to various parts of the lake. Another kind is built on the marshy edges of the lake and is not moved, although it still floats. These gardens can be up to 2m in thickness, and can grow root crops such as carrots, turnips and radishes, as well as the same vegetables grown in Bangladesh: tomatoes, cucumbers, okra, aubergines, beans, gourds, chillies, melons and pumpkins and herbs. They can be 45m in length, and 3m wide. Unfortunately, the gardens are currently badly affected by climate change, pollution, tourism, and reduction in the area and depth of the lake. Government policies of resettling the farmers elsewhere, and the reluctance of younger people to work for the low profit margins involved also threaten the survival of this form of cultivation on Dal Lake.

Other countries in Southeast Asia, such as Cambodia, Vietnam and Myanmar, which have a tradition of houses built on stilts over a lake, also use floating gardens. Further afield, I have found a reference to floating vegetable patches in Southern Sudan.

All of the floating gardens described above are simple to build and are constructed of locally available materials. They are cultivated using organic methods, basically lake mud and animal dung rather than industrially-produced fertiliser.  They can provide a living for landless farmers, and empower village women, who can do much of the work. They usually supply food to a nearby city, so they are distributed locally and food miles are minimal. But cultivating a garden while up to your waist in water and mud, and the low profit margins involved, are not to the taste of many young people today. Floating gardens are labour-intensive – you can’t use a tractor or a harvesting machine on a raft. Pollution from sewage and industrial waste is becoming a problem in many areas. It takes extreme poverty, or a crisis such as the Covid pandemic or serious flooding to make them an attractive option in the modern world. But one day, we may need to think again.

* Incidentally, the sale of water hyacinth is now prohibited in the UK, and although it is not illegal to have some in a garden pond, releasing it into the wild is strictly forbidden. It does not usually grow well here because it does not tolerate winter temperatures below freezing, but has been noticed thriving in a Nottinghamshire park. Shall we think about global warming at this point….?