Agapanthus have never flowered

i had this same problem up until 2years ago.
i was puzzled why mine did not flower
i started feeding mine with chicken manure pellets twice a year and now they flower.
dont know if the pellets helped or it was just their time but now they flower strongly.

I repotted mine and then they flowered quite well. I'm wondering if 12-13" is bit enough for 3 plants? Also how deep is the pot? Is it in sun or shade? Do you feed them? I went to Madeira a few years ago and they grow wild there along the sides of the roads in great swathes - very beautiful.