St. John’s Wort
Hypericum perforatum
PhotosCurtesy of Collin G. Wilson
Origin. Europe.
Distribution in Canberra Region. Widespread in disturbed and open areas including woodlands, grasslands, pastures, riverine areas, and roadsides.
Dispersal. Seeds dispersed by wind and animals; vegetative growth from roots (rhizomes).
General Description and Biology
An erect perennial herb or small shrub with a creeping rootstock.
Usually multiple stems to 80 cm high, emerging from a crown.
Leaves, when viewed against light, show characteristic oil glands.
Flowers bright yellow with 5 petals in numerous clusters on ends of stem-branches, in spring/summer;
later the dead brown flower stalks are clearly visible.
Readily invades unimproved overgrazed pastures.
Reproduces both from crowns and roots and by seed that germinate in autumn, winter and spring.
Seeds are dark-brown or black, 1mm long, cylindrical and pitted. Up to 33,000 seeds per plant per season. Dense seedling growth occurs after fires.
Roots are stout, growing up to 100 cm deep, with lateral rhizomes growing horizontally, producing buds that form new aerial growth. Slashing promotes such new growth.
St John’s Wort is extremely invasive and competes strongly with native vegetation.
Control Methods
a. Manual.
Rosettes (springtime) can be pulled out including roots, preferably when soil moist.
If already in flower, remove and bag whole plant including roots.
b. Chemical
Glyphosate spray can be effective at the seedling stage or during flowering but before the fruit turns brown. Repeated applications needed for larger plants. Specific sprays also available.
Seek advice of CNP/CUPP. Only trained staff of CNP/CUPP or qualified contractors can use the sprays and specific herbicides.
See notes at the end of section on Herbaceous plants: General methods of control.
See also CRC Best Management Guide #7 for more details.