Sometimes these guys are slow to wake up in the spring. I know my pink hibiscus haven't started to bloom at all either. My reds and other cultivars are chugging out the blooms.
You could up the fertilizer some, that should nudge them along.
Barb

The hibiscus I have puts out white blooms that look like dinner plates! It grows bigger every year and I have a hard time getting it to stand tall. I now have it tied with string to the rails of my deck to hold it up. Does anybody have a solution for me other than tying it with string?