Hoya serpens seems to be one of those plants that fall into the category of plants I could grow well at one time, but not any more. I have flowered this plant a number of times, and it really is spectacular especially when you compare the size of the blossom to the small size of the leaves. It really requires conditions that are very hard for me to achieve to do it’s best. Ideally temperatures in the high 60′s to low 70′s with lot of humidity will grow this plant like a champ. I can give it humidity and high temperatures, which will produce lots of new growth, but it will not flower. I can give it cooler temps with low humidity;the leaves yellow and fall off under this scenario. Tough plant to have success with unless you live in the right area of the country. I do however recommend that everyone try this Hoya, because a well grown specimen is a sight to behold!
Here is a link to a time-lapse video of Hoya serpens blooms in motion: http://youtu.be/R7HeGY9hbYs