While images of veranda cafes, cathedrals and automobiles have relentlessly presented Saigon as a city born from the streets, in truth it grew out of a swamp. Burning of coastal mangroves lining the Saigon and Dong Nai Rivers not only cleared the way for urban growth but also powered river commerce. Like the human and non-human inhabitants of these mangroves, the wood had almost no status, subject to waves of cutting and pyrolysis. When petroleum arrived, city founders put the tank farms at this smoking, coastal edge. This urban-swamp interface became critical as the city's edge against disease, too, where sailors disembarked to be tested and city sewage passed from outlets upstream. Out beyond these industrial and microbial checkpoints, Saigon's underworld thrived, notably the powerful Bình Xuyên mafia network. After 1945, the mangrove's unique nature shifted it into the spotlight for would-be insurgents and city-builders. This paper considers the evolving relationship of the city to the mangrove as a form of eco-political symbiosis. Where once the city grew through the mangrove's destruction and consumption, rising tides, erosion and floods have brought new attention to Saigon's green fringe.