In 1920, Hugh Landon and his second wife, Jessie Walker Landon, began to develop Oldfields' landscape and gardens. Inspired by a garden they visited in Maine that had been designed by Percival Gallagher, an associate of the famed landscape architecture firm Olmsted Brothers, the Landons hired Olmsted Brothers, working with Gallagher to refine their property. It was Gallagher's vision that transformed Oldfields into a fully developed American country estate, anchoring the house firmly in the landscape and providing dramatic views and pleasant garden walks.

Among Gallagher's designs for Oldfields were the tree-lined Allée at the front of the house, the estate entrance and redesign of the Formal Garden. The Ravine Garden, spread upon a hillside between the house and the Indianapolis Water Company Central Canal, was one of Gallagher's most significant contributions to the Oldfields landscape.