Agapanthus (Agapanthus praecox )

Family: Liliaceae

Growth Habit: This species does not have any aboveground stems, except for the long flowering stalks. These are green, round in cross-section and hairless. They are quite thick and have hollow centres. The very large and strap-shaped leaves are produced in clusters of up to 20 glossy leaves, 20-70 cm long and 3-5 cm wide, at the base of the plant. These leaves are relatively thick and somewhat fleshy or leathery in nature, with veins running lengthwise. 

Type of Plant: A large and long-lived (i.e. perennial), clump-forming, herbaceous plant growing up to 1 m tall.

Flowers: The flowering stems, up to 1.2 m tall, bear a single large, dense, and almost spherical cluster of numerous (i.e. up to 100) blue to mauve or white flowers at their tips. The flower cluster is 9-12 cm wide. Flowers appear in November and December.

Mature fruit and seeds

Fruits/Seeds: The fruit is a relatively large, 50 mm long,  and somewhat elongated three-sided capsule . These fruit turn from green to pale brown or straw-coloured as they mature, and split open to release their numerous (20-100) seeds. These seeds are black, flattened, and have a wing-like projection.

Dispersal: This species reproduces via large numbers of tiny seeds. Seeds are spread by wind or water.  It can also reproduce vegetatively via its short creeping stems (i.e. rhizomes). Also spread into natural areas through dumped vegetation or contaminated soil.

Distribution: Known to invade roadsides, bushland and waterways throughout Tasmania. 

Status: Not declared in Tasmania, it is actually regarded as one of the worst environmental weed species in some parts of the state. Areas infested include the coastal areas in the north-west of the state (i.e. in the Cradle Coast Region), the Latrobe municipality west of Launceston, and the Greens Beach/Kelso Coastal Reserve on the central north coast of Tasmania.

Weed Impacts:

  • Dense clumping roots are capable of displacing other native understorey species and can prevent the regeneration of trees and shrubs. 
  • Can dramatically change species diversity and eliminate habitat for native fauna. 
  • Relatively fire retardant and so may change fire regimes in infested areas. 
  • Spreads quickly down drainage lines and can cause localised flooding.
  • The leaves and roots of this species are considered poisonous to humans and its sap is a skin irritant.

Control Methods:

  • Plant alternatives in your garden. For example: Tasmanian Falx-lily  (Dianella tasmania), Lomandra longifolia, Liriope  (Liriope muscari ‘Evergreen Giant’)  or Kangaroo Paw ( Anigozanthos species). 
  • Do not dump garden debris or soil.
  • At a minimum, dispose of all flower heads before the set seed.
  • Dig out clumps and all root and rhizome material.
  • Agapanthus is relatively resistant to herbicides. A permit is available in Tasmania until 2022 for Metsulfuron-methyl,  600 g/Kg (cut and paint, weed wipe and spot spray) and glyphosate (cut and paint or use of weed wiper on leaves). 
  • Mowing and slashing will stop the spread of Agapanthus via seed but not necessarily stop the spread vegetatively. If you do this frequently and keep new foliage from growing, over time, it may reduce the vigour of the plant and kill it.
    Agapanthus spreading through a mown lawn

N.B. Always check the herbicide label before use.