Robert served as park superintendent at Minneopa State Park from 1936 to 1939, supervising Works Progress Act projects and planting many trees that still thrive today. Frieda operated a concession stand in the park in a building that is now a visitor center. Robert and Frieda hoped the Ulmen Homestead would be included within the park's boundaries, and after Robert's death in 1995, the land was sold to the park so the public could also enjoy its beauty.