Winterthur occupies a virgin tract of hardwoods, and my count of the rings of a white oak on the lawn (sawed down in 1997) showed that it was more than 300 years old. As historian Margaret Lidz describes (1999), Colonel du Pont played an important early role in saving the majestic trees, laying out the road system, and installing the Pinetum (1918). His son, Henry Francis, established March Bank (1902) and consulted Coffin as early as 1910. She was a close friend of the family, had trained at Massachusetts Institute of Technology when Henry Francis was at Harvard, and had afterward traveled with him in Europe. In 1928, following the enlargement of the house, Coffin designed the circular drive at the new front door; the Boxwood Scroll Garden (northeast corner of the house, 1930); the terrace with its existing tulip poplar trees (then sixty feet tall, today closer to 100 feet); and the long stairway to the swimming pool (with James M. Scheiner). In 1955, she was summoned back to turn the tennis courts into a Sundial Garden.
Coffin's designs were executed with plants chosen by Henry Francis du Pont himself. Several garden structures came from the country house Latimeria (1815, E. I. du Pont with William Warner), which once stood on Newport Pike near the foot of Broom Street, Wilmington. From Latimeria, du Pont acquired for the Winterthur garden (1929–1930) an octagonal summerhouse, beehives, a mushroom-top circular bench, latticed Chinese pagoda, and double gates (most have been heavily rebuilt). Near the end of his life, du Pont created a Quarry Garden (1962). Uphill from the museum, a wall from Mansion Farm, south of New Castle, with “1750” set in glazed bricks in the gable, is incorporated into a modern structure (1964) formed from an old water tower.