It will bloom when it is ready. The buds on many Hoya sp. develop slowly, and nothing you do will speed up the process. It is just the nature of how they grow.

You should be feeding your hoyas, regardless. I use the tomato food (MiracleGrow) because:

1. It's cheap

2. It has all the macro- and micro-nutients

3. It comes in handy formulations (water soluble, time release, and liquafeed, which I can just attach the liquageed sprayer on my hose)

4. It works for me