St. John’s-wort

Identification & Biology
Alias' : Klamath weed, goatweed
Latin Name : Hypericum perforatum
Category : Terrestrial Plants
Description :
  • Perennial with short rhizomes
  • Grows up to 1.0 m tall
  • Stems are 2-sided, rust coloured with numerous branches
  • Oval-shaped opposite leaves are covered with transparent dots
  • Bright yellow flowers with five petals that have black dots


St. John’s-wort seeds can germinate in the spring or fall, and new stems emerge from woody root crowns in the spring. Flowering occurs over the summer. One plant can produce over 100,000 seeds per year that spread by wind, water and animals. Seeds also have a gelatinous coating that aids long-distance dispersal and can survive in the soil for up to 10 years. Plants dry up in the fall and dead stems can remain standing for many months. St. John’s-wort is widely known for its reported anti-depressant properties. It has been used for centuries to treat mental disorders and nerve pain. In ancient times, herbalists wrote about its use as a sedative and a treatment for malaria, as well as a balm for wounds, burns, and insect bites.


In British Columbia, St. John’s-wort grows at low- to mid-elevations in coastal, grassland, and open forested regions. It is commonly found on rangeland, pasture, meadows and along roadsides and disturbed areas. It has adapted to dry, gravelly, or sandy soils.

Impact & Risks
  • Toxic compounds in St. John’s-wort can cause photo-sensitivity in grazing livestock (cattle, sheep, goats, horses), loss of weight and even death in rare circumstances if consumed in sufficient quantities.
  • It can reduce the productivity of pastures for livestock and threaten the ecological health of natural areas.
Prevention & Mitigation

The most effective way to ensure that your lands do not become infested with St. John’s-wort is by prevention. Here are some recommendations to prevent St. John’s-wort from invading your property:

  • Maintain your crops and natural lands in a healthy, vigorous condition to ensure a competitive plant community; competitive perennial grasses and forbs utilize water and nutrients that would otherwise be readily available to St. John’s-wort.
  • Regularly patrol your property for St. John’s-wort plants and immediately control or remove infestations before seed set. Do not leave plants to compost as they may still produce viable seed.
  • Cooperate with adjacent landowners and encourage them to prevent St. John’s-wort spread.
  • Immediately re-vegetate disturbed, bare soils with a suitable seed mixture that provides dense, early colonization to prevent weed invasion.
  • Do not move contaminated soils to a new area.
Treatment & Disposal
  • For small infestations, a combination of herbicide treatment and seeding can be effective.
  • Tillage followed by seeding of perennial grasses and legumes is another method of control.
  • Removal of the stems by any means (grazing, fire, defoliation) stimulates re-sprouting.
  • Hand-pulling/digging cannot effectively remove the extensive root system.
  • Foliage feeding Chrysolina beetles have proven very effective at controlling this weed, and is considered the first success story of B.C.’s biological control program dating back to the 1950s.
  • Before applying herbicides, read the label for full use and precautionary instructions.
  • For further information on the selection and application of chemicals to protect your crop, contact AgriService BC at 1-888-221-7141 or email
Okanagan Distribution

Priority Level Definitions

Watch For - Poses a significant threat (very high risk) and does NOT presently occur in the region OR is relatively new to the region and is very limited in extent.
High - High risk/impact; limited population with significant potential to spread in the region.
Medium - Medium risk/impact; limited distribution – broader population distribution with potential to spread further in a region.
Low - Low risk/impact; may be widespread or not, may be of concern in specific situations with certain high values – e.g. specific agriculture crops. Some species may be treated primarily with biological control agents.