Spring (March to May) is the best time to visit Mount Heng: the mountain flowers — azaleas and magnolias particularly — are in bloom, the weather is cool, and the light is good for walking. The spring flower season draws large Chinese crowds, especially on weekends, but the mountain is big enough that the trails never feel dangerously packed.
Summer brings heavy humidity and frequent cloud. The mountain is often above the cloud layer, which can create dramatic effects, but visibility from the summit is unreliable. Autumn (October to November) is a quieter and pleasant alternative to spring. Winter brings genuine cold to the upper elevations, and the summit temple can be iced over. The cable cars operate year-round but may suspend service during severe weather.
The major pilgrimage festivals bring the largest crowds: the Spring Festival period (Chinese New Year) and the Mid-Autumn Festival are both very busy. If you want a quieter mountain experience, a weekday visit outside peak periods is notably different from a weekend in high season.