Real estate the one thing we're not making any more of. That might be good news for landlords but not for the world's farmers, who have finite cropland to feed a growing global population. The answer: build up by farming vertically. Valcent, a company based in El Paso, Texas, is pioneering a hydroponic-farming system that grows plants in rotating rows, one on top of another. The rotation gives the plants the precise amount of light and nutrients they need, while the vertical stacking enables the use of far less water than conventional farming. But best of all, by growing upward instead of outward, vertical farming can expand food supplies without using more land.