This Month in Photo of the Day: Nature and Environment

Some green roofs can be far simpler to create than traditional roof gardens. Volunteers from Cook + Fox installed the New York City architectural firm's roof themselves using Green Paks. The polyethylene bags, marketed by St. Louis-based Green Roof Blocks, contain low-maintenance plants and can be laid out with no preparation beyond rolling out a layer of waterproof material that controls drainage and blocks the intrusion of roots into roof structures.

See more photographs from the May 2009 feature story "Green Roofs."