Urban Farming, a nonprofit group that plants crops for the needy on rooftops and other unused spaces in cities, has launched a vertical agriculture project at four locations in and around downtown L.A. The four new urban farms employ the green wall system developed by Green Living Technologies, a series of modular, 2 foot by 2 foot by 4 inch, stainless steel panels divided into growing cells that are mounted to a building facade. The four L.A. edible walls are between 24 and 30 feet across and 6 feet high and have been planted with bell peppers, hot peppers, tomatoes, cucumbers, tomatillos, strawberries, spinach, leeks, and a variety of herbs. Members of the community will maintain the gardens and harvest the food.

Now that green roofs have become accepted, if not yet common, a growing number of designers seem to be exploring the next great frontier in living architecture – green walls.

This past February in Paris I stumbled across the Musée du Quai Branly and was blown away by its 8600-square-foot Plant Wall designed by Patrick Blanc. A horticultural tour de force, Blanc’s creation reportedly includes more than 150 different plant species. A portfolio of Blanc’s living walls can be found on his website.

I’ve seen a number of spectacular green roofs both in the U.S. and Europe (my current favorite is the new roof on Queens Botanical Garden’s LEED Platinum Visitor and Administration building, one of the few planted with native species). Because green walls are even more visible to the public, they’re bound to capture the fancy of landscape designers. They could even revive the venerable tradition of the garden folly. Case in point: Gas Design Group’s “Topiade” (topiary + façade) overlays for an existing Louis Vuitton store.

By the way, living walls can have some if not all of the environmental benefits of green roofs: They can reduce storm-water runoff, trap and break down airborne toxins, and by decreasing the urban heat island effect, help keep cities cool.