Hoya sulawesiana is an exceptionally slow growing plant in my experience, and if I had to guess why I have had so much difficulty with it, I would guess it is because I’ve watered it too much. Having hard waxy leaves, and in nature growing primarily epiphytically, it would require very little water. I finally after two years grew a decently looking specimen using mostly coconut husk chips as a substrate, and watering much less. This is a plant that can easily go two weeks without water.