Well its that time of year when the seed heads of Agapanthus are forming. The plants by themselves are not too bad as they hold the soil together so in some instances where the soil is unstable they are best left and deheaded.
On the other hand the seed can travel down creeks into the areas of bushland and take root on creekbanks and unusual places like gutters. The root fragments can be spread in the movement of soil and dumped plants can survive for years and take root where they are left.
Agapanthus are tough plants so they have been used extensively on edges and next to drains. All of these drains and run off lead into the bushland. So if we remove the seeds the plants can not move into the surrounding bushland.