It's not a Chia Pet -- it's your house, with plant-covered walls and a roof garden reaching toward the sky. Vines and roof gardens have been around for millennia. The Hanging Gardens of Babylon were one of the Seven Wonders of the Ancient World, remember? But nowadays, green roofs and living walls aren't just valued for their looks. Plants fight pollution by absorbing noise and recycling carbon dioxide. Plants on the walls also add a layer of insulation. They lessen the effects of the urban heat island, cutting utility bills for the home. Some water purification systems use green vines to treat water for recycling. Of course, let's not forget the main benefit -- it's really neat to wander up to your roof to pick some lettuce and tomatoes for tonight's salad.