Athenaeum Hotel

Forty-five years on, the French botanist's gardens have grown massive in scale. One inside a Portuguese shopping mall is larger than four tennis courts, and there's one in Kuwait that's almost as big. But Blanc's recently completed facade for the Athenaeum hotel in London

(shown) could be his most high-profile project yet. Looming over Green Park, it's an eight-story antigravity forest composed of 12,000 plants.

Blanc uses a kind of techno-trellis as the underlying structure: A plastic-coated aluminum frame is fastened to the wall and covered with synthetic felt into which plant roots can burrow. A custom irrigation system keeps the felt moist with a fertilizer solution modeled after the rainwater that trickles through forest canopies.

But plants for this vertical landscape must be chosen with care. Because the walls are so high, conditions vary widely. The shade at ground level is perfect for rare Asian nettles; on the brighter upper stories, plants that usually cling to windblown cliff faces brave the blustery British breezes.

Blanc, who still has a fish-tank setup in his apartment, says his creations will always reach upward: "I leave horizontal gardens to others. I only think vertically."