We are unable to say why your double white Camellia drops its buds as you describe. You say you water the border regularly, that the drainage seems good, and the plant healthy. These conditions, and the temperature you keep the conservatory at, should induce a fine display of bloom. The only suspicion we have is, that as your border is only 1 foot wide, and the hot-water pipes pass near it, the roots, that are no doubt matted against the brick-work, may get very dry at times, even though the general mass of the soil may be all right; and in this way a check is given to the plant, resulting in the dropping of the flower-buds. You should examine this part of the case, and give more water if required, and syringe overhead till the blooms open.