that's not actually the case, David85 - what they like is lime free soil, which isn't quite the same thing as acid soil, though the presence of lime means alkalinity, certainly. They will grow perfectly well in neutral soils too, and the fact that yours has healthy leaves means its happy with the growing medium as it is. I'd try raking in some sulphate of potash around the base during June, though you may find, as its the third year, that it produces flowers this time round anyway. Applying the potash will increase the chances of flowering for next year.