The 10th lunar month or around September is the period when farms yield the biggest amount of crops. So, in the past the local people decided to offer their products to the spirits. The people believed that the time between the 1st to the 15th day of the waning moon in the 10th lunar month is when the spirits of their ancestors, particularly ones that have not yet reincarnated, will be released from the underworld. On this occasion, those still alive make merit by giving food offerings to Buddhist monks and dedicate merit to the dead.
The merit making starts on the first day of the festival. Fifteen days from this day the spirits of the dead will go back to the underworld. The people then arrange a merit making ceremony again on the last day of the festival, to which most people attend.