PA25 tow pilot with glider in tow reports NMAC with another glider at 50 feet landing opposite direction.

Narrative

I caused an NMAC at a grass strip glider operation with occasional GA traffic. Normal operation is tow out on Runway 18 and land Runway 36 to minimize occupied runway time. Wind was 6-8 kt from ~ 330; broken cirrus skies with bases ~ 4000 AGL. I was unaware that Glider 1 was on left base or final for Runway 36 while the PA25 (me) and Glider 2 began departure roll on Runway 18. When the PA25 became airborne Glider 1 became visible and appeared to be at approximately 50' to 80' fully committed. Both PA25 and Glider 1 altered course to increase separation. Rate of closure was ~ 100 mph and the estimated 1450 feet remaining between the two aircraft would have been consume in less than 9.8 seconds had altered courses had not been initiated.I towed Glider 1 to 3000' AGL; returned; refueled; and taxied into position to connect to Glider 2. Glider 1 released northwest of the field. The PA25 was angled at 45 degrees to the active to minimize prop wash on the glider; maximize view of downwind; and complete checklist. Wing runner ran to tell me of Glider 2 intentions as radio was INOP. I picked up an announcement from Glider 1 and simultaneously removed one headset to hear wing runner. I assumed from the partial that Glider 1 was at the north IP in lift; our standard announcement prior to entering downwind. I looked thoroughly toward the northwest for Glider 1; did not see it and proceeded to take up slack rope. PA25 received standard Soaring Society of America take off signals from wing runner and Glider 2 PIC. Returned rudder waggle and departed Runway 18 announcing we were rolling on 18. The PA25 became airborne and Glider 1 became visible on final for Runway 36.Critical misses: The announcement from Glider 1 was a partial - he announced downwind not at the IP. Wing runner waited until slack was taken up to clear the area. I cleared the northern quadrant not knowing that Glider 1 was in the southern quadrant. I convinced myself of a false position for Glider 1 I failed to confirm Glider 1 position & intentions via radio. Avoidance action: I initiated a left turn toward the alternate runway. Glider 1 altered course slightly toward left side of Runway 36. Glider 2 followed me and released west of the field. Lessons Learned: Avoid letting distractions disrupt the safe routine. Make confirmations - not assumptions clear the area all the time - not just prior to departure. One announcement may be missed - additional announcements don't cost anything. Announce position more often. Take inventory - know which aircraft are in the air. Our safety training was invaluable and both pilots reacted promptly with correct decisions and reactions.