In the dog days of summer, cut your AC some slack and turn instead to the Greenmarket for relief. There you’ll find an August harvest of juicy, cooling watermelon with a surprise beneath its green-marbled rind: The flesh inside is yellow—not red. Known as “iceboxes” for their fridge-friendly size (typically seven to ten pounds), yellow watermelons—with breed names like Yellow Doll, Buttercup and Sorbet Swirl—are honey sweet, with a firm, lightly seeded flesh that’s as delightful to eat as it is to behold. “They’re so much sweeter than the big honking red ones,” says Susan Blew, owner of Oak Grove Plantation in Pittstown, New Jersey, which sells mini melons at the Union Square Greenmarket. “I grow for flavor, not size,” she adds. It takes the watermelons nearly three months to ripen, hence their late-summer arrival, timed conveniently to the hottest days of the year. And while many customers are initially shocked at the vibrant canary hue, Blew says, more often than not, they come back for seconds: “Every year we grow more and more, and there are never enough,” she says. “People tell me they eat the whole thing themselves—they don’t like to share.” Grab two (one for you, one for a pal) while the temperature still soars—come September, these sunshine-colored beauts will have gone the way of the heat wave. Available at Oak Grove Plantation, Norwich Meadows and Hodgson Farm stands at the Union Square Greenmarket (Union Square Park); Mon, Wed, Fri, Sat; $1–1.50/lb; or at the Brooklyn Kitchen (100 Frost St at Meeker Ave, Williamsburg, Brooklyn; 718-389-2982), $2.29/lb.