August Haarstick did an apprenticeship in gold and gold. Silversmith and passed his master's examination in 1911. After the death of his father in 1905, he took over the family business and continued it as a silversmith.
August Haarstick was a staunch opponent of the war and got to know the Worpswede art nouveau artist Heinrich Vogeler in a pacifist association, with whom he had a long friendship. August Haarstick was a member of the Deutsche Werkbund and took part in many exhibitions at home and abroad, e.g. 1930 in Rio de Janeiro.