Autumn (late September to November) is the best season: the rice harvest turns the terraces golden, the weather is cool and clear, and festivals are more likely. The Dong New Year — celebrated in the eleventh lunar month, typically November — brings singing, drum tower gatherings, and the best chance of catching a genuine Dong Grand Song performance.
Late May to early June is the second good window: the paddies are newly flooded for planting and reflect the sky in silver sheets. The humidity climbs after mid-June.
Winter can bring mist and cold that is atmospheric rather than pleasant, though the light on the bridge in the early morning fog is remarkable. July and August are hot and crowded with domestic tourists.
The terraces look their best in the golden hour before 9am and after 5pm on any clear day, regardless of season. Stay overnight in the village rather than day-tripping from Guilin to experience this.