Chinampas are human-made islands built in shallow lakebeds that have fed the people of Mesoamerica and shaped local ecosystems for over a thousand years. Sometimes referred to as 'floating gardens,' these agricultural feats of engineering survive as a testament to the ingenuity of the Aztec civilization and their lake-dwelling predecessors, particularly the ancient peoples of Xochimilco, where chinampas are still in use today.

The word chinampa derives from the Nahuatl term chinamitl, meaning "a fence made of plants" or that which could be enclosed within a fence of plants. The labor-intensive process of building a chinampa began with locating a firm floor in the shallow area of a lake. There, laborers would drive wooden posts into the lake bottom. The designated area for the construction was usually rectangular, with lengths varying from 8 to 100 meters and widths ranging between 2 and 25 meters. Along with the posts, laborers planted willow trees, such as Mexico's native bonpland willows (Salix bonplandiana), in the corners or along the perimeter, where the roots of the trees would give structure to the nascent chinampa. The Florentine Codex depicts a willow tree growing out of blue waves; its simple, lance-shaped leaves that alternate along the stem are characteristic of the water-loving Salix genus.

With the posts in place to establish the structure of the artificial island, laborers wove reeds, vines, and branches between them to create the enclosure from which the chinampa derives its name. Once the fence of plants was completed, laborers began the arduous task of filling the enclosure with many layers of soil, at least some of which would have been scraped from the bottom of the lake itself, thus fortifying the fence with mud and further plant material. Once the chinamitl was stable and the raised mud and soil reached a height of 50 cm above the surface of the water, the top layer of soil was left to dry for several weeks before the land was used for planting.

To control floodwaters and promote moisture content in the soil, laborers constructed sophisticated drainage systems including dams, sluice gates, ditches, dikes, and canals. Flowing between chinampa fields, the canals served as waterways and allowed those who worked the land to transport supplies, crops, and fertilizer directly to and from the artificial fields in the lake shallows. Capillary action drew water into the layers of soil in the chinampa, allowing adjacent canals to serve as reservoirs for an integrated subirrigation system that met the water needs of the crops and created a microenvironment that protected them from frost. In addition to the aquatic infrastructure required to sustain the chinampas, water reservoirs and fish weirs – fences placed in flowing water to direct the motion of fish – could also be constructed to set aside water for different tasks and to expedite fishing.

In order to ensure the ongoing fertility of these human-made agricultural islands, farmers, known as chinamperos, employed a number of fertilization methods. One of these methods involved transferring mud, soil, sediment, and vegetation from the bottom of the canals to the top layer of the artificial fields. This process helped to maintain the canals while also renewing the topsoil of the chinampas for better planting. The soil from the canals contained a high build-up of organic material from decomposing plant matter, animal waste, and other waterborne debris, which facilitated water retention and kept crops from losing too much moisture during the dry season. This allowed for year-round cultivation, made efficient through the use of seedbeds to prepare new crops for planting even while others were being harvested. Adding fresh topsoil from the canals also helped to aerate the chinampas and promoted long-term fertility and high productivity. Other methods of fertilization included applying compost (including food waste, ash, charcoal, and excrement) and other organic materials. Using crop residue as mulch also helped to suppress the growth of weeds.

With careful maintenance, chinampas in the time of the Aztecs could host a huge array of crops and flowers. Today's chinamperos, keeping alive the agricultural tradition, cultivate crops including maize, legumes (bush beans and fava beans), amaranth, tomatoes, peppers, lettuce, radish, seepweed, purslane, and many more. While the ancient peoples of Mesoamerica would not have had access to nearly as many domesticated animals, most of which are not native to the Americas, modern chinamperos often keep animals like chickens, cattle, swine, and sheep, feeding them on excess produce and adding their manure to the fertilization process.

After hundreds of years, the chinampas still make it possible to grow crops in a lacustrine environment and promote the health of the local ecosystem. Within the chinampas themselves, the native willows planted at the perimeter of the fences serve as more than structural support. Fast growing and anchored by dense root systems that help prevent soil erosion, broad crowns of willow branches and leaves provide shade and create barriers against wind and pests. As the trees grow taller, they also provide a natural trellis on which vine crops can climb to facilitate better access to sunlight.

The microecosystem of the chinampas also supports biodiversity and plays host to beneficial bacterial and fungal species. Because so much of the layered soil in the chinampas comes from the lakebed, algae, bacteria, and macrophytes proliferate in the soil. These organisms consume and convert the nutrients from decaying organic matter, storing excess nitrogen and phosphorus as a survival mechanism for use in nutrient-deficient conditions. Through this process, these bacteria increase the nitrogen reserves of the soil. When new soil is added to the surface, it introduces more organic matter and moisture, feeding the algae, bacteria, and macrophytes and propagating the nitrogen-fixing cycle.

As an example of raised farming, chinampas are similar to structures from other parts of the Americas, including the raised gardens of Lake Titicaca, and other raised farming techniques have been recorded in regions including the Netherlands, Denmark, Russia, France, and Bangladesh. In all of these cases, raised farming techniques promote soil quality, aeration, and moisture content through drainage, and in some cases, like Mexico's chinampas, this technique enables agricultural production in environments where it would otherwise be impossible. While this was not an innovation of Aztec agriculture, it was perfected under the sway of their empire such that, in the 15th and 16th centuries, the chinampas of Mesoamerica fed hundreds of thousands of people.

When the Mexica (pronounced "Me-SHEE-kuh") people came to the Valley of Mexico, they found a land already dominated by other cultural and ethnic groups, and they depended on mercenary work to sustain themselves. After years of wandering in search of political security, the Mexica resolved to build their home on Lake Texcoco, taking a location that no one else wanted and transforming it into the heart of an empire. The Aztec civilization that rose from those swampy waters was so enduring that the symbol of the city's god-given founding portent – an eagle seated on a cactus eating a snake – remains the central element on the flag of Mexico today.

Part of the reason that no other people had settled the region around Lake Texcoco was that Mesoamericans depended almost wholly on agriculture for sustenance. Supplemented by game animals and a very select few domesticated species, Mesoamerican peoples primarily ate fruits and vegetables and thus required a great deal of agricultural infrastructure. With little arable land around Lake Texcoco, chinampas emerged as an elegant and effective solution to the problem of food. The early Aztecs were most likely inspired by their rivals in Xochimilco, which means "flowering fields" in Nahuatl, where chinampas were already flourishing before the founding of Tenochtitlan. Resolved to thrive in their newfound home, the people of Lake Texcoco set about filling the shallow waters with farmland.

The Florentine Codex describes a type of land called atlalli, which is a combination of atl, meaning "water," and tlalli, meaning "earth," in Nahuatl. In describing what makes this land unique from other forms of tlalli, the Nahuatl author tells us, "This is the irrigated field. It is a watered garden, one which can be irrigated…it is good, fine, precious; a source of food, esteemed; a place of fertility…to be planted to maize, to be planted to beans, to be harvested" (Book 11, folio 227v - 228r, translated by Anderson & Dibble). The image below shows a farmer at work, standing between tendrils and pools of water. The artist signifies the fertility of the land not only through the contrast of textures between the curling water and the tufted earth but also by the presence of stems and flowers, particularly some that resemble corn plants, near the end of the branches of moisture.

Over the course of the nearly two centuries of Aztec rule, chinamperos tended to the artificial island farms, and the government controlled and regulated all aspects of maintenance with an emphasis on economizing the use of time, produce, and waste. In fact, the fertilization of the chinampas was integrated into the lavatory practices of the people of the city. Inhabitants of Tenochtitlan relieved themselves in specialized huts built near city streets and alleys, where canoes would collect the human excrement. From there, it was transported directly to the chinampas, where it would be used as fertilizer along with plant matter and other nutrient-rich organic material. In addition to the fertilization methods mentioned above, Aztec chinamperos left their farm-islands fallow after two or three years of use to allow the soil to rest before further cultivation.

Through this carefully organized system, Aztec-era chinampas could support seven different crops in their year-round cycle. Crop productivity was maximized by allowing seeds to germinate in seedbeds before being introduced to the chinampas. While other crops grew in the full-sized plots, farmers planted seeds in small squares of soil called chapínes, where they grew for a few weeks before being transplanted into the chinampa soil, fertilized, and gently covered with a layer of native straw and reeds. This layer of vegetation would protect the new seedlings from the sun and help trap the humidity in the soil. Finally, the crops were sprayed with a solution of ground chiles and water to control pests. Once fully grown, the crops were harvested, loaded directly into boats, and sent to the bustling markets that surrounded Tenochtitlan.

The Aztecs, like many Indigenous American populations, employed, among other plants, a sort of sacred trinity of food crops: corn, beans, and squash. Sometimes known to Indigenous populations as "The Three Sisters," these species thrive when planted together in a shared space because each of the crops provides some form of support for the others. Corn plants provide a natural trellis on which bean plants climb to thrive, and bean plants absorb nitrogen from the air, which they convert to nitrates that help fertilize the surrounding soil. Squash leaves provide ground cover that inhibits soil evaporation and the growth of weeds, ensuring their neighbors' access to moist, nutrient-rich soil. While the Aztecs would not have used the title "The Three Sisters" to describe their intercropping techniques, corn, beans, and squash were nonetheless staples of the Aztec diet, and the chinampa farming zones on Lake Xochimilco produced enough crops to feed approximately 100,000 people during the height of the Aztec empire.

The Florentine Codex preserves an image of corn described as cintli: "the white maize ear—that of the irrigated lands, that of the fields, that of the chinampas." (Book 11, folio 246v, translated by Anderson & Dibble)

In addition to the crops needed to sustain Tenochtitlan's population, Aztec chinamperos often planted flowers in their floating island plots. Far from simply being a source of beauty, flowers were symbolically important throughout Mesoamerican cultures. Known as xochitl ("SHOW-cheet") in Nahuatl, flowers were also offerings in Aztec sacrifice rituals. Three deities who had particularly associations with them, Xochipilli, Xochiquetzal, and Macuilxochitl, were worshipped as patrons of the arts, beauty, and pleasure. Xochitl in cuicatl, meaning "flowers and song," was a metaphorical turn of phrase in Nahuatl that could be used to refer to all manner of artistic endeavors, particularly the deeply valued Aztec art of poetry. Whether worn by dancing women during celebrations, carried to signify the presence of a god on earth, or offered to honor the gods on sacred days, the flowers of Tenochtitlan grew on chinampas.

Recent surveys show that chinampas were in use in Mesoamerica as early as 1000 BCE, and though most of the great lakes that once housed the heart of Aztec civilization were drained long ago, a few chinampas still feed the people of Mexico City after hundreds of years. While there are about 5,000 acres of extant chinampas, only about 2.5 percent of those are still used for agriculture, and the chinamperos that farm them employ both traditional and modern techniques.

Besides their cultural, agricultural, and social value, the chinampas also represent the last natural haven for axolotls in the wild. Named in Nahuatl, like the irrigated land itself, after atl ("water") and the Aztec god Xolotl, axolotls are critically endangered amphibians whose unique regenerative capabilities – they can regrow limbs, eyes, and portions of their brains – make them an active subject of medical research. They were well known to the Aztecs and seem to have thrived in the basin of Mexico before the conquest, despite being a particularly esteemed part of the Aztec diet, described in the Florentine Codex as "a meal fit for lords." (Book 11, folio 68r, translated by Anderson & Dibble).

Today, scientists estimate that there are about 50 to 1,000 individuals left in the wild, and the combination of urban expansion and the decline of the cultivation of chinampas for agriculture has drastically reduced their habitat. The infrastructure of the floating farms, particularly the small canals that branch from larger waterways, provide axolotls with refuge from the invasive carp and tilapia, introduced to the ecosystem in the 1960s, that compete with them for food resources and prey on their young. The ecosystemic relationship between these unique amphibians and Mexico's farm-islands is enshrined on the 2021 50 peso note, which depicts an axolotl suspended in rippling canal waters, surrounded by crop-filled chinampas, and fenced in by the willows and reeds that form the salamander's natural habitat. In the background, a corn plant rendered in ethereal gold rises like the sun, and the text commemorates the environment of Xochimilco in its status as a UNESCO World Heritage site.

Invaluable to the axolotls, modern chinampas also benefit local human populations by providing ecosystemic services, including water filtration, microclimate regulation, increased agro- and biodiversity, regulation of water levels, and the capture and sequestration of greenhouse gases. But the mere presence of chinampas cannot provide these services without care and maintenance. A number of agencies and organizations are actively pursuing conservation efforts to preserve and revitalize the chinampas of the basin of Mexico, but the trends are not promising.

Even with ambitious local initiatives, the outlook is alarming. A projection for the year 2057 assumes that in Xochimilco, without a concerted effort from the involved players (particularly farmers and local government), most current chinampa land will be converted to housing.

(Ebel 2019)

Now, as in the time of the Aztecs, caring for and cultivating chinampas is a labor-intensive process. Today, a few people safeguard centuries-old farming techniques, and relatively few strive to sustain the whole system of chinampa agriculture from what would seem to be its inevitable decay. In 2022, researchers estimated that 90 percent of chinampas in Xochimilco and the surrounding area had been abandoned, and while the pandemic stoked some interest in the efforts to revitalize chinampas and further support chinamperos, Alejandra Borunda, writing for National Geographic magazine, noted that chinampas represent "1,000 years of history, still alive for now." (Borunda 2022).