To develop Grifola frondosa as a new commercial product, we investigated the optimal primordium formation method for bottle cultivation. Primordium formation was initiated on the sixth day in all treatments, but in the T7 treatment, which consisted of removing old spawn and turning the bottle upside-down, was initiated on the ninth day. The ratio of primordium formation was at its highest value, 98.9%, in T3 and T7. Among the treatments, T7 produced the highest quality fruiting bodies and a mushroom yield of 112.8 g in each 850 mL bottle, but its crop cycle time was somewhat longer than those of the other treatments. These results indicate that appropriate methods for primordium formation in bottle culture could enhance mushroom quality and productivity