Most Tea Olives need to reach maturity before they will bloom well, 5-6 feet is the standard height for the more hardy varieties of Osmanthus to begin blooming. Are your leaves serrated heavily or have they started to become more smooth. The smoother leaves tend to imply maturity. There are 4 varieties of Osmanthus and all but one need to reach maturity before blooming reasonably well, and that variety is much less hardy than others. If they're growing well just realize that they do have to reach at least a certain height/maturity. I prefer Osmocote which has a nice slow release and includes all the 11 micronutrients as well. Besides just treating it well there's nothing you can do to hurry it up.