How do you decide what to plant in a green roof bed? What will grow best? What will grow at all? We asked Richard Hawke, the Garden’s plant evaluation manager, about the plants they selected to evaluate in the Green Roof Garden. Talking in the shade of mature trees near the Plant Science Center, where the plants are being stored until they are installed, we learned what grows best in the clay medium of our roof garden, and what experiments we’ll be trying to grow in our first year of plant trials on a roof.