Green Offshoots

October 28, 2009, The New York Times — Mario Casasnovas was on the green roof of the Bronx County Building a couple of weeks ago, remembering the flowers there in the summer and offering some tips about handling the sedum that is the main plant on the roof. “The roots from the clover,” a weed, “tend to wrap around the roots of a sedum,” he said, nine floors above the Grand Concourse, near Yankee Stadium. “You’ve got to be careful not to pull out the sedum with the clover.”