Gaertner exhibited in 27 Cleveland May Shows and his paintings hang in galleries throughout the country, including the CLEVELAND MUSEUM OF ART, Metropolitan Museum, Chicago Art Institute, and Whitney Gallery. He painted the fresco in the Cleveland Greyhound bus station. Gaertner is best known for his Ohio landscapes, with their dark, dramatic skies. He traveled frequently to Cape Cod, Hudson River Bay, the Allegheny Mts., and the Monongahela Valley to find variety in landscapes, but always returned to the Chagrin Valley and his farm in Willoughby. Gaertner won the Natl. Academy of Design Award in 1953 for an oil painting entitled "Barge Men." His portrait hangs there in tribute to him. He was president of the CLEVELAND SOCIETY OF ARTISTS and the Carl Gaertner Memorial Prize in painting is offered at the Institute of Art.
Gaertner's subject matter varied, but certain themes recur in his work, including industrial subjects, with Cleveland as his model in the early part of his career. Other themes were Provincetown, West Virginia watercolors and oils, and Chagrin Valley paintings. After 1935, Gaertner bought a farm in Chagrin Valley and began his series of paintings of that subject.
