The surname is a fairly common one in Germany. In my branch of the family, it originated in Napoleonic times (late 18th/early 19th centuries) when Jews, traditionally known as A-the-son-of B, were required to adopt surnames. Originating in France, the policy was widely adopted in neighbouring countries.
My great-great-grandfather worked as a gardener in a small castle, Schloss Schoenbusch in southern Germany. He adopted the name of his occupation, Gaertner, as his surname. My father anglicised it to Gardner when he migrated to Australia.