Chinampa

A chinampa is a long narrow growing bed built up out of shallow standing water. Channels are dug through a wetland or lake edge, and the mud and rotting vegetation lifted out is piled into ridges between them, until there is planting surface where there was none. It is not a raised bed that happens to sit beside water: the channel makes the bed and the bed shapes the channel, and neither works alone. It is sometimes called a floating garden, which is wrong - living willow stakes driven round the edge root into the bottom and hold it in place.

The channels are the irrigation. Water soaks sideways and upward through the bed from the water standing either side, so the crop is watered from below with no pump and no pipe, and the height of the bed above the water line is what decides whether that works. Channels of real size are needed for it, around 1.5 m (5 ft) deep and 4 to 6 m (13 to 20 ft) wide, because a narrower ditch neither yields enough material to raise a bed nor holds enough water to feed it back. The ground this suits is ground already too wet to farm, and the site has to hold a permanent freshwater level rather than drying out between seasons.

What keeps it going is dredging. Silt and water weed are lifted from the channel and spread on the bed, which feeds the growing surface, keeps the channel deep enough to irrigate from, and keeps it open as a route to move people and harvest by boat. Stop that and the channel silts in and the beds revert to wetland, so the labour is not upkeep but the mechanism itself. Two things undo a chinampa. If the water level falls, the bed becomes organic soil left in the air and it oxidises away from underneath rather than merely drying out. And because the crop drinks the water beside it, whatever drains into the channel from upstream arrives on the food, so what happens upstream matters as much as anything done on the bed.