This hoya has always seemed to want more than do most of its hoya brethren; mostly more water and more space. Soon after he first arrived in his 3-inch pot (7.6cm) there were roots coming out of every bottom opening of the pot and the medium was always dry. He clearly needed a larger pot, and I wanted to move him to my standard bark/sphagnum mix. With that accomplished, it wasn’t long before there were roots visible in the new mix.
He set buds on an existing peduncle, but they soon blasted. I finally realized that he wanted quite a bit more water than he was getting. Now I give him a thorough watering once a week, and a mid-week touch-up. The extra water had made the difference. There are now two more peduncles and they flower regularly, very regularly. It seems that this plant is almost always in bloom for me.
In my setting, Hoya multiflora seems fine with standard household humidity. He likes a well draining and airy mix, but I include just a very little bit more long-fiber sphagnum moss. Given the right conditions, he develops a very extensive root system, very quickly, so plant it in a container that is slightly larger than what you think appropriate for a hoya. That root system is looking for water, so make sure that you water regularly. If it’s blasting buds and not blooming, increase the water frequency little by little.