St Johns Wort

Hypericum perforatum
Family: Hypericaceae

Growth Habit: An erect plant which grows up to 1.2m in height, averaging 0.6 to 0.9m. The plant tends to be woody near the base. Leaves are a paler green on the underside and have visible oil glands.

Type of Plant: St Johns Wort is a perennial, which usually dies down over winter and re-emerges from underground stems in spring.

Flowers: The five petalled yellow flowers grow in clusters. Each flower is approximately 15 to 25mm in diameter and appears to have black dots that are actually glands.

Fruit/Seed: Seeds are released in late summer.

Dispersal: Reproducing from underground stems and seeds.

Distribution: Several small infestations of St Johns Wort occur throughout Tasmania. These are usually roadsides and run down grazing land.

Status: Secondary and Prohibited in Tasmania.

Weed Impact:

  • St Johns Wort contains substances known to cause illness in livestock, such as photosensitisation of unpigmented parts of the animals skin.
  • It is also a valued medicinal plant by some herbalists.
  • It is capable of infesting large areas of grazing land, particularly in drier climates.

For further information contact the Department of Primary Industry, Water and Environment, Tasmania.

Control Methods:

  • Grubbing. Isolated plants and small infestations can be removed using hand tools, ensuring the root system is also removed.
  • Herbicides. Spot spray for smaller patches and boom spray for larger areas. Herbicides registered in Tasmania include 2,4-D, triclopyr and glyphosate.

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