Born in Chicago and raised in Pittsburgh, Dahl received a B.S. in landscape gardening from Pennsylvania State College in 1917. He spent two years in the Army before returning to Penn State to earn an M.S. degree, and went on to teach there as Assistant Professor of Landscape Architecture for another five years. In 1927 he left to work for the State of Pennsylvania before going into private practice as a landscape architect, engineer and site planner.
Dahl, a Baha’i by faith, traveled to Chicago in 1926 to visit the selected site for the first Baha’i temple in the U.S. Concerned with the lack of a cohesive landscape design for the building, he offered his services as landscape architect. He moved to Chicago in 1936, but it wasn’t until 1938 that he was approached by the trustees of the Baha’i House of Worship to design the temple’s landscape. While continuing work on the project, Dahl relocated to Charleston, West Virginia, where he worked as the Associate Chief of West Virginia State Parks, and later to Louisville, Kentucky, where he was Associate Director of the Kentucky State Parks and partnered with designer and engineer Carl Berg. In Louisville, Berg and Dahl opened the Cloverleaf Garden Center to supply their projects.
Work began on Dahl’s design for the Baha’i House of Worship Gardens in 1951. In retirement Dahl moved to Michigan, where he continued to work on the finer elements of the design and management of the grounds until his death.