Here are the specifications of the conditions that made Hoya yuennanensis flower for me. Potting substrate was coconut husk mixed with 20% large sponge rock (Perlite). Went outside in June to increasing day length hours, and flowered as the day length shortened in late August. Temperature ranged from day time highs of up to 85 F to night time lows down to around 50 F. Watered with nutrient solution once per week.