St John's Wort

(Hypericum perforatum)

St John's Wort 

What is St John's wort?

  • St John's wort is a weed of pastures, open bushland and roadsides.
  • St John's wort is a declared weed in Tasmania under the Tasmanian Weed Management Act 1999. The importation, sale and distribution of St John's wort are prohibited in Tasmania.

How to identify St John's wort

  • St John's wort is a perennial (long-lived) herb growing to between 30 and 70 cm and occasionally to 1.2 metres high. The reddish stems arise from the rootstock or woody crown.
  • St John's wort has a main root extending to 1 metre deep and horizontal rhizomes (underground stems) just below the surface producing buds from which new above-ground growth develops each year.
  • The leaves are stalkless and hairless and have numerous small oil glands that give the leaf a perforated appearance when held up to the light. The flowers are bright yellow with black glands dotted along the margins of the petals, and grow in numerous clusters at the end of the branches. The fruit is a sticky capsule containing numerous, dark brown or black cylindrical seeds.
  • A related weed, square-stemmed St John's wort (also called St Peter's wort) is similar to St John's wort, but stems are almost square in cross-section, and the leaves are oval to oblong, often heart-shaped, and stem clasping at the base.
  • For further help in identifying St John's wort, search the Dennis Morris Weeds and Endemic Flora database for St John's wort illustrations. If you are still in doubt about the weed you are dealing with, contact Biosecurity Tasmania on 03 6165 3777 for help.
St John's Wort St John's Wort
Image top: St John's wort flower, © K Stewart, DPIPWE.
Images above L-R: St John's wort in flower & infestation, © K Stewart, DPIPWE.

St John's wort in Tasmania

  • St John's wort occurs as a localised weed of roadsides, poorly managed grazing land, neglected areas and disturbed bushland areas of Tasmania, particularly in the northern Midlands, north-east, central north coast and the south east.
  • St John's wort is a threat to the grazing industry due to its toxicity to stock, and its ability to compete with desirable pasture species in poorly managed pastures.
  • St John's wort is also an environmental weed and can out-compete native species, with open grassland-woodland communities most affected.

What is the legal status of St John's wort in your area?

  • The legal responsibilities of landholders and other stakeholders in dealing with St John's wort are laid out in the Statutory Weed Management Plan for St John's Wort.
  • Use Table 1 (Zone A municipalities) in the Statutory Weed Management Plan to find out whether your area falls in an eradication or containment zone.
Detailed management and control guidelines for St John's wort can be found in the St John's Wort Control Guide. Refer also to Herbicides for St John's Wort Control. For further information see Weed Links and Resources.

See also
Herbicides for St John's Wort Control
Statutory Weed Management Plan for St John's Wort
Weed Links and Resources

Other useful links
Pest Genie
Weeds in Australia - Weed Management Guide for St John's wort

St John's Wort Control Guide


  • Plan your control program, this will save time and money in the long-run;
  • Consider the impact of your control methods on off-target species, especially if herbicides are used;
  • Ensure machinery and equipment is washed down between sites or prior to contractors leaving site;
  • Get in early - For new infestations, eradicate before the plants reach the flowering stage: once plants begin seeding, control becomes more difficult and expensive;
  • Carefully time your use of herbicide for best results (see Herbicides for St John's Wort Control for more information);
  • Coordinate your control program with neighbouring landholders where your weed problem crosses property boundaries;
  • Revisit and regularly inspect the site and ensure follow-up is undertaken;
  • Use a combination of different control methods; and
  • Establish vigorous pasture (or native species) after removal to reduce re-infestation.


  • Don't introduce St John's wort to St John's wort-free areas (e.g. by failing to wash down machinery and equipment between sites);
  • Don't start your control program without first planning your approach;
  • Don't allow St John's wort to flower and set seed before treatment;
  • Don't rely on one attempt at removal - follow-up is essential;
  • Don't rely on just one control method.

Spread of St John's wort

  • St John's wort spreads by seed and by vegetative means (crown and rhizomes).
  • Seed is the main means of spread. A mature plant can produce between 15,000 and 30,000 seeds. St John's wort seed may remain viable for at least up to 20 years.
  • Seed is spread by wind, in water and soil, and as a contaminant of agricultural produce. The sticky capsule attaches to animal wool and fur, clothing and can also survive the digestive systems of most stock.
  • Cultivation, earthworks and roadside machinery can spread pieces of the crown or rhizomes to clean areas where the fragments produce new plants.

Avoid the introduction of St John's wort

  • Preventing the introduction of St John's wort to clean areas is the best means of control. Good hygiene practices are vital.
  • St John's wort is easy to identify when in flower, and small isolated infestations should be removed as soon as possible, preventing further spread.
  • See the Washdown Guidelines for Weed and Disease Control for detailed information on how to wash-down equipment and personnel to reduce the chance of spreading St John's wort.

Physical removal

  • Isolated plants and small infestations can be removed by hand, preferably before seeding.
  • Remove as much of the root system as possible as St John's wort can sucker from roots left in the ground.
  • Follow-up will be required to deal with any further germination or suckering.


  • St John's wort can be set back by cultivation which exposes and dries out the roots, then sowing to pasture.
  • The developing pasture should be left un-grazed for the first year to allow the subterranean clover maximum chance to smother the St John's wort.
  • Over-grazing will favour the weed as it reduces the competition from the pasture plants.
  • Grazing programs need to be well planned and carefully managed to ensure stock do not suffer poisoning.


  • Burning should not be used to control St John's wort. Burning stimulates reshooting and suckering and can worsen an infestation.

Chemical control

Herbicides for St John's Wort Control

Herbicides for St John's Wort Control

Important Disclaimer
To the extent permitted by law, the Department of Natural Resources and Environment Tasmania (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using information or material (in part or in whole) contained on this website.​