Agapanthus will eventually grow into quite a big plants so plant them about 30cm apart. It does depend on the look you want to achieve - do you want a border of agapanthus - in which case plant them 30cm or less apart. If you want them spaced out use 45cm spacing. Good luck!

Agapanthus are more likely to flower if they are congested. I achieved this by taking a plastic flowerpot, cutting the bottom off it and burying it in the garden. I then planted three agapanthus inside it and they flowered in their second year