without the sunlight, roots attached, totally living. i call it living lettuce, living salads, living vegetables. >> who says lettuce can't grow on trees? >> exactly. >> show me ws ino of ow i wor >> what we have in the base is the water. the nutrient solution. the water that's filled with our minerals which is what makes a plant taste good. it pumps through the center here. and then it trickles down. uses 12 minutes of energy an hour. it runs for three-minute cycles. >> then it gets air the rest of the time? >> yeah, air and sun. >> reporter: there is something timeless unfolding on this rooftop. because hydroponics as a basic concept is an ancient idea. as ancient as babylon's hanging gardens. but it's always had an air of experimental to it. not a solution embraced by the world's farmers, in part because it's so unconventional and can be expensive to set up, as well as needing a lot of monitoring to keep the system functioning. but mooney is a believer. in addition to running the