Known as Bunny and born to a wealthy family, Mellon attended Miss Fine’s School in Princeton, New Jersey, and Foxcroft School (a girls’ preparatory school) in Middleburg, Virginia. Although she received no formal training in horticulture, it proved a lifelong avocation. Inspired by the work of Andre Le Nôtre and modern artists such as Piet Mondrian, the hallmark of Mellon’s gardens was her eye for detail, both in the plantings and the construction. At the request of Jacqueline Kennedy (to whom she was a confidant), and working with landscape architect Perry Wheeler, she redesigned the White House Rose Garden in 1961, and also worked on the White House East Garden (dedicated as the Jacqueline Kennedy Garden in 1965). She designed plantings for the John F. Kennedy Presidential Library and Museum in Boston, collaborating with the firm Kiley, Tyndall, Walker, and architect I.M. Pei. Her planting design can also be seen at the President John F. Kennedy Gravesite. One of her most significant designs was that for her own private garden at her 4000-acre estate, Oak Spring Farms, near Upperville, Virginia. There, Mellon amassed an extensive collection of rare botanical prints and horticultural volumes, which now comprise the Oak Spring Garden Library. She garnered many awards for her horticultural designs, including the Conservation Service Award from the Department of the Interior in 1966 for her work at the White House.