Why are agapanthus so popular? It must come down to them being so tough and the attractive blue (or white) flowers. Their toughness and ability to survive without water for long periods also makes them have great weed potential. If you have ever tried to dig one out you will see they have a good grip on life.
If you have them planted and live in an area with lots of native vegetation then one way to prevent them spreading is at least to remove the flower heads before they set seed. Take care disposing of the heads send them to the tip.
You may have guessed that agapanthus growing in the bush or grasslands are not my favourite plants so it was interesting to see these plants at the Cressy Cemetery recently. I wonder if they will survive the fire.