Five years ago, under the cloak of darkness, New York–based floral designer Lewis Miller packed his team and 2,000 dahlias and carnations into a van, and headed for the John Lennon Memorial in Central Park. Working swiftly, they arranged the blooms around the perimeter of the circular black-and-white mosaic, and fled—leaving behind an anonymous highlighter-hued halo that quickly drew a crowd. The altruistic act stood in contrast to Miller’s typical work for private events, high fashion brands, and museums; he later called the guerilla installation one of the most rewarding he’d ever produced.