INSIDE THE CAVERNOUS INTERIOR of a former Boston-area taxi depot—walls covered in graffiti, pools of water on the concrete floors—three gleaming green-and-white containers sit side by side. The steel boxes are former “reefers”—refrigerated shipping containers used to transport cold goods. Bone-chilling rain is falling outside, but inside the 320-square-foot boxes, it’s a relatively balmy 63 degrees, and the humid air is heavy with the earthy smell of greens. Filling each box are 256 neat vertical towers of plants, bathed in a noonday-intense pink light.

The...