This happens sometimes with roses and lilies - usually, the cause is a new hybrid of something, which then reverts to whatever it was bred from - its as if the new genetic information doesn't hold... Are yours new hybrids, or varieties? Or old, well known ones?

Hello amjsj! Is is possible your agapanthus has a virus which can cause colour distortion in the flower? Are the flowers totally white or did they start blue but now have stripes of white in them? If the latter, then I believe this is a virus, and your only resort is to replace the plants. As bamboo suggests the age of the plants may be important, and the older the plant the more likely it is to be a virus. Sorry. Hope this helps.

Also, did you plant a few white ones with the blue, and/or let seed set. Most white forms of Agapanthus are more vigorous than the blue ones, and will eventually out-compete them.

Whatever they are quite lovely, I have a very small clump that only increases by one extra flower every year!!

I agree! Beautiful Agapanthus! I notice that they aren't so much white as light blue. What have you been feeding them? I prefer a formula with 3-1-2 proportions, and the extra potash helps encourage deeper color. If it is in extremely sandy soil, it may also be missing aluminum, which also encourages the blue color. If so, try scratching in some generic brand, untreated kitty litter to provide aluminosilicates--it will also reduce your watering needs.

Thank you tugbrethil - your response to the above has made me realise what my blue hudrangeas need next spring/summer ... aluminium sulphate! Thank you so much. In case you don't pick up this message I will broadcast ...