I bought some Begonia tubers from a nursery , 2-3 inches wide , rounded one side and dried up what look like roots on the other where it dips in the centre. How are these planted . Have been told the rounded bit at the bottom and the top ( dinted , hollow at the top) and not to cover completly with compost . -On 2 of them some pinky soots coming from the hollowed out centre. Is this the top ? and do I need to soak the night beforeplease ?