Bradley's Idle Hour farm was also known as the "Lucky B" because he named most of his horses with "B" names. Blue Larkspur raced in Bradley's silks, white with green hoops and cap, and was by Black Servant. Black Servant was a son of Black Toney, who also sired Kentucky Derby winner Black Gold). Black Servant was second in the 1921 Kentucky Derby, right behind his Idle Hour stablemate, Behave Yourself.

Bradley also won the 1926 Kentucky Derby with Bubbling Over (sire of Baby League, who was the dam of Busher), the 1932 Derby with Burgoo King, and finally the 1933 Derby with Broker's Tip. But his loss in 1921 with Black Servant badly rankled him, even though another of his horses took home the roses. He was furious with Black Servant's jockey, Charles Thompson, who had apparently defied orders to take back. (Rumors flew that Bradley had a lot of money riding on Black Servant, as did many Idle Hour employees.)

Blue Larkspur's dam was Blossom Time, by North Star III. Blossom Time's dam was Vaila, an influential mare imported by Bradley.