Council has called on residents growing the common plant to remove the seed heads before they open and release their potentially invasive seeds.

A native plant of southern Africa, agapanthus have rapidly become one of the Highlands' most common garden plants, enjoyed by many residents for their pretty purple flowers and year-round green leaves.

However, at this time of year when the flowers die back, the plant has the potential to spread beyond the neighbourhood garden and threaten the shire's diverse bushland, wetlands and other natural areas.

Council's waste education projects officer Esther Landells said it was important for residents to not dispose of the seeds in their garden organics bin.

"The seeds of the agapathus plant are very robust," Ms Landells said.

"When we receive green waste at the Resource Recovery Centre it's sorted, shredded, pasteurised, monitored and checked over many months before being reused in parks and gardens."

"Despite all these processes, there is still a slim chance that some agapanthus seeds may survive."

Instead, council recommends residents bag the spent seed heads and dispose of them in their red-lidded domestic waste bin.

"If gardeners are trimming or removing an entire agapanthus plant, the leaves and stems can still be placed in the green organics bin," Ms Landells said.

"However it's really important that if gardeners wish to get rid of the seed pods they don't place them in their green bin."

Council's open spaces team leader Jen Slattery said while many people saw agapanthus as a plant which required no maintenance, that perception "couldn't be further from the truth".

"It's really important that owners get out into the garden and cut the seed heads off before they open and the seeds get blown around in the autumn winds," Ms Slattery said.

Agapanthus is listed by council as an environmental weed that has the potential to spread readily into bushland and along creeks, together with the likes of English Ivy, Privet and Willow trees.

Council has produced a full-colour environmental weeds brochure which is available online at www.wsc.nsw.gov.au/environment or through garden clubs and Bushcare groups throughout the Highlands.