We recommend avoiding the summer because there is a risk of heavy rain at this time of year. The trails are so slippery and therefore dangerous; we refuse to organize any walk at this time of the year. In winter (December to March), it will not be possible to hike in the Tibetan region of Shangri-la as it’s too cold. If you can choose your month to come trekking in Yunnan, then we recommend April and May as well as October and November.