Best known for being the Superintendent of the Minneapolis Park system from 1906-1935, Wirth spent his life in horticulture and park administration, planning, and development. Born in Switzerland, he grew up in Winterthur where his father was a schoolteacher. He was the second of four children of Johann Conrad and Martha Wiget Wirth. His father helped create summer camps and other outdoor activities for children, and Theodore loved accompanying his father on walks and adventures in the beautiful countryside and mountains. He showed an early interest in horticulture and became apprenticed to a horticultural firm for three years as a young man then he took a course in engineering at the Technicum in Winterthur, which enabled him to become a professional gardener. After working for a time in Zurich for the National Exhibition, he traveled to both London and Paris to broaden his perspectives. He was employed by a grower and florist in London, where he went to the Covent Garden flower market each day. He also worked in the Jardins des Plantes in Paris and when he returned to Switzerland he first worked at a large estate, but because he wanted to study English in night school, he took a job as the City Gardner of Zurich.