On May 6, 1993, at 0830 eastern daylight time, an Extra 300, N694DM, collided with a tree on a private airstrip near Ridge Springs, South Carolina. The local personal flight operated under 14 CFR Part 91 with no flight plan filed. Visual weather conditions prevailed at the time of the accident. The commercially rated pilot, with private single engine land privileges, received serious injuries, and the airplane sustained substantial damage. The flight departed Trenton, South Carolina, at approximately 0800 hours. According to the pilot, he departed Trenton en route to Barnsville, South Carolina, but encountered weather conditions and decided to divert to his airstrip in Ridge Springs. Reportedly, he established a 90 knot approach speed and touched down on his normal spot. After landing the pilot experienced difficulty stopping the airplane on the water soaked sod runway. The airplane rolled off the departure end of the east runway and collided with a tree. According to the pilot, the normal landing distance for this airplane is 1500 feet; the pilot did not report computing the required landing distance for a landing on the wet sod runway. No mechanical problems were reported.