To get help I think this question needs a bit more info Guest? Such as what compost are you growing it in, where you are growing it and how are you feeding it?

Drc's right - could give you the simplistic answer that it needs acid soil, but for all we know, if its in a pot, for instance, it could be potbound, or the leaves turning yellow could just be older leaves which are about to fall, or it could be short of magnesium, or it could be its one that needs shade and gets too much sun..