Chinampas: The Floating Gardens That Fed an Aztec City

By the year 1500, the Aztec capital of Tenochtitlan held more people than London or Paris at the time — somewhere around 200,000 residents, all living on an island in the middle of Lake Texcoco. There was no surrounding farmland to feed them. So the Aztecs built their farmland instead, one narrow strip of reclaimed lake at a time. Those strips were called chinampas, and they were so productive that some plots produced food seven times a year.

How chinampas were built out of mud, reeds, and living trees. Why Lake Texcoco's shallow water made this kind of farming possible. How chinampas helped a lake-bound city feed a quarter of a million people. Where you can still see working chinampas today.

Farmers started by staking out a rectangle in the shallow water of the lake, usually about 30 meters long and 2.5 meters wide — roughly the size of a modern bowling lane. They wove fences of reeds called petates around the edges, then piled in layers of mud dredged from the lake bottom and decaying plants pulled from the water. Mixed together, this became rich, dark soil. At each corner, farmers planted a willow tree called an ahuejote. As the tree grew, its roots spread underwater and locked the whole plot into place so it wouldn't wash away.

Rows of chinampas were separated by narrow canals just wide enough for a canoe. Farmers paddled between their plots instead of walking, hauling mud, seedlings, and harvested crops by water. The canals also worked like a natural irrigation system — the plants' roots reached down into the moist soil and could pull up water even without rain, which mattered a lot during Mexico's dry season.

Because the soil stayed damp and fertile year-round, a single chinampa could be harvested up to seven times a year — compare that to ordinary dry-season farmland nearby, which usually managed one or two harvests. Farmers grew maize, beans, squash, chili peppers, tomatoes, and flowers, often on the same plot at the same time. Historians estimate the chinampas surrounding Tenochtitlan may have covered over 9,000 hectares (about 22,000 acres) and supplied a large share of the food the capital needed.