Easily the most eye-catching display at the Go Green Expo was the wall full of living plants that drew attendees over to check out Philly Green Wall & Roof. It's certainly something you don't see every day, though you may see it more often if these folks get their message through to enough homeowners.
The benefits of the "green roof" - i..e covering your roof with growing plants - are already well-established. The newest twist, though, is to apply the same practice to exterior walls, conferring an additional aesthetic benefit that previously was only visible to people who were invited up onto your roof.
According to "Green Wall Editor" George Irwin, whom you can hear on the attached two-minute podcast from the Expo (recorded during a particularly boisterous point, so there is some distortion here and there), a green wall allows you to grow not just decorative plants but functional, edible crops on your wall. Somehow, and you can get more information here, the technology allows roots to "migrate" around on the wall while still remaining firmly affixed within the vertical firmament.
Obviously, this is aimed squarely at urban dwellings, where space for planting in the ground can be severely limited. It's a fascinating trend among many initiatives to "green" our cities, and you can even find some of these already in Philadelphia. Who knows how many more we'll see if this trend catches on?