On Governors Island, just a five-minute ferry ride from Manhattan, art professor Sam Van Aken plots his fantasy orchard. He plans on opening a public park with 50 blossoming trees that bloom into a mosaic of pinks, reds, purples, and whites. Come summer and fall, after the flowers have faded, visitors will be able to leisurely pick among 200 rare varieties of peaches, plums, apricots, cherries, and apples. Van Aken is a master at grafting, an agricultural practice that involves transplanting one type of tree stem onto another, forming a…