Look out, Backyard. You've got some competition. Space-challenged apartment and home dwellers have gone vertical and greened their rooftops with plants, flowers, grass, even vegetables— all with wonderfully lush results. Here are a few of our favorites:

(Images: 1. Urban Garden Casual; 2. Living in Comfort and Joy; 3. Brooklyn Roof Garden; 4. TreeHugger; 5. Cactus Jungle; 6. Gleicher Design Group; 7-8. New York Magazine; 9. Living Roofs)