Future Cities: Singapore focuses on the exceptionally forward-looking urban approach of the island nation, to learn about the challenges of planning for future generations.

(CNN) Less than 20 miles from Singapore's skyscrapers is a completely different set of high-rise towers.

Much smaller in scale but with a big ambition, over 100 nine-meter tall towers at Sky Greens vertical farm offer a new vision of urban sustainability.

Green vegetables like bak choi and Chinese cabbage are grown, stacked in greenhouses, and sold at local supermarkets.

The idea of vertical farming goes back to the 1950s, but Jack Ng, farm owner and inventor of the system in place at Sky Greens, has patented elements of his design.

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The plants don't get overstressed under the sun and at the same time they can get nutrients in the water equally. Jack Ng, Sky Greens

Slowly rotating on water-powered, aluminum A-frames, the vegetables pass through a trough of water every eight hours. The water powering the frames is recycled and filtered before returning to the plants. All organic waste on the farm is composted and reused.

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