Here's a summary of info from an agapanthus question on the "Ask a Question" forum:
Agapanthus bloom best if they get full sun and adequate water. After they are well established, they are fairly tolerant of drought and high temperatures. They do like to be root bound, whether in a pot or in the ground. It does not like to be divided or moved, and will sulk for a year after a move.
Wait until they are almost busting the pot before you move them up, and you'll get more blooms from them.
I have found some are hardy in my zone 6 garden in the ground if planted up next to the house and kept dry in the winter.