they naturally grow in areas of ristricted root run apparently. Have you replanted them into an open space.

I read that if planted in a pot they like to be crowded and then they will flower.

I have just replanted mine (probably far too late I know) from the garden to pots because they were not growing at all. I've seen wonderful ones in pots in neighbouring gardens.

i dont think its true about being restricted maybe you should split them up and then feed them now for next year

Copy and paste the link below for the RHS info on growing agapanthus

http://bit.ly/rsC8AT

Youngalistai most folk seem to think they grow best when slightly crowded.