The pilot reported that he departed from a soft grass runway and used the entire runway length. During the takeoff roll, the airplane accelerated much slower than what he was used to in the soft grass, but still believed he would have enough airspeed to climb. After clearing a fence at the end of the runway, he reported the flight controls felt "mushy," the right wing dropped, and the airplane entered an aerodynamic stall. During the stall the right wing impacted the terrain and the airplane came to rest in a field upright. The pilot stated there were no mechanical malfunctions or failures with the airplane that would have precluded normal operation. During a post-accident inspection, a Federal Aviation Administration Aviation Safety Inspector reported the airplane sustained substantial damage to the right wing.