Longwood Gardens, founded by Pierre S. du Pont in the early 1900s, is about to get another dose of du Pont. The Kennett Square, Pennsylvania, gardens and The Conservation Fund will acquire and operate the longtime du Pont estate Granogue located in New Castle County. The 505-acre private estate includes the long-time residence of the late IrĂ©nĂ©e âBripâ and Barbara …