Marks & Spencer has added three vertically farmed salads to its UK shelves: Citrus Sorrel Baby Leaves, Spicy Baby Leaves and Baby Garlic Kale, developed in partnership with Italian vertical farming company Planet Farms. The leaves grow indoors under UV light in a soil-free environment with controlled temperature, water and nutrient delivery and are then packed within 60 seconds of harvest. According to the retailer, the salads stay fresh roughly five days longer than a conventional supermarket bag and need no washing.

The environmental numbers are eye-catching: 96% less water than field-grown salad, around 97% less fertilizer and no pesticides. But M&S is pushing equally hard on flavor. Citrus sorrel and garlic kale aren't standard salad-aisle fare, and a controlled indoor environment lets Planet Farms grow varieties that would be hard to produce consistently in open fields.…