Hoya serpens will be blooming any day now and is covered with buds! H. serpens has not bloomed for me in three years, and it will be the first time for this particular plant that I started from cuttings also 3 years ago. I got so mad at the mother plant, that this one was started from, I gave it away! When serpens goes downhill, it really goes downhill in a big way. Leaves turn yellow almost overnight and removing them becomes a daily reminder of your failings as a plant keeper!
I will give you some hints about this plant that I have picked up after keeping it for over eight years. If it is growing OK, do not transplant it – you will regret it! It will grow like crazy in a warm humid atmosphere – it will be very unlikely to bloom under those conditions. It does not want to grow in too light and porous a mix – my first one grew and bloomed in regular peat based potting mix. It will grow well under lights, but will never bloom there unless you can find a timer that will increase the day length by 2-3 minutes a day for months. It likes humidity and will drop leaves if grown in too dry an atmosphere. If the air is dry, mist it as much as possible. Keep it cooler, but don’t go crazy – mine bloomed with temperatures ranging from 65°F – 75°F (18°C – 23°C).