Callas are finicky, so I understand your delema. Whatever you do remember these 3 things when dealing with callas.

1.Full Sun
2.Standing Water
3.Time release fertlizer

If you do this correctly you will have a nice clump to seperate in about a year. Callas can be tricky for the novice. If you are dealing with developmentally disabled you might want to "get thier confidence up" with elephant ears, there are some attractive species out there, plus they can be difficult to kill.

P.S Make sure there is adequate air circulation inside the greenhouse, otherwise the plants will be most unhappy this christmas.