Ziegler and his wife were great lovers of the arts, particularly paintings. Karl and Maria would present each other with paintings for birthdays, Christmases, and anniversaries. They amassed a large collection of paintings, not necessarily of one particular period, but of paintings they enjoyed. Maria, being an avid gardener, particularly enjoyed flower paintings by Emil Nolde, Erich Heckel, Oskar Kokoschka, and Karl Schmidt-Rottluff. Karl enjoyed pictures of the places that he and his wife called home, including pictures of Halle and the Ruhr valley. Forty-two images from their shared collection were incorporated into a foundation, bequeathed to the Mülheim Ziegler Art Museum.