Posted: 23/07/2016 at 17:45
Perhaps you used ericacious compost after seeing references to L. auratum and L. speciosum, which the RHS list among acid-lovers?
The only thing I can add to what you've already been told is that black tips on lily leaves can be caused by over-watering, but I don't see any significant blackness on your photo. As long as their pots are not soggy, your lilies should be fine. The leaves will still feed the bulb after the flowers are gone, as they normally do.