My mother has started collecting succulents (taking her on a greenhouse tour of the twin cities was how I ended up getting interested in Stapelias). Anyway, she's boughten two Black Aeoniums (they have fancy cultivar names but I dn't recall them both were about the same) and both have had their leaves dry up crispy and fall off from the bottom up. Once you water the whole plant falls apart and the stem turns to mush. This has happened with two different black Aeoniums from two different greenhouses. Any ideas on what she's doing wong?