The pilot of the tailwheel and tundra tire equipped airplane reported that during landing on a soft grass airstrip he conducted a wheel landing instead of a three-point landing. The pilot further reported that during the landing roll, the main landing gear dug into the ground, which resulted in a nose over and substantial damage to both wing struts and empennage. The pilot reported that there were no preimpact mechanical failures or malfunctions with the airframe or engine that would have precluded normal operation. According to the FAA Airplane Flying Handbook FAA-H-8083-3A; SOFT-FIELD LANDING The tailwheel should touch down simultaneously with or just before the main wheels, and should then be held down by maintaining firm back-elevator pressure throughout the landing roll. This will minimize any tendency for the airplane to nose over and will provide aerodynamic braking. The use of brakes on a soft field is not needed because the soft or rough surface itself will provide sufficient reduction in the airplane's forward speed. Often it will be found that upon landing on a very soft field, the pilot will need to increase power to keep the airplane moving and from becoming stuck in the soft surface.