Of all the places on campus you’d expect to find a garden brimming with kale, Swiss chard and collard greens, the second floor of University Crossing probably isn’t one. But thanks to a collaboration between the university and Lowell-based urban farming nonprofit Mill City Grows, there’s a new rooftop vegetable garden outside the windows of the busy second-floor landing at the student and administrative center. UML’s hope is that the space helps educate passersby about the university’s Urban Agriculture Program. A wall sign provides details about the “Green Roof” garden and other urban agriculture sites around campus. Producing fresh, leafy vegetables for the university community is an added bonus.