Common St. John’s Wort
Common St. John’s Wort is also known as:
- Common Goatweed
- Klamath Weed
- Tipton Weed
Flowers: The bright yellow flowers have five petals that are 8 – 10 mm long. The flowers are inflorescences with 25 – 100 flowers per cluster.
Stems: Mature plants are rusty red and can be 0.3 – 1.0 m tall. The stems are erect and smooth with multiple stems per plant. The base of the stems are woody and become branching and leafy in the upper half.
Leaves: The leaves are thin and elliptical with a rounded base and distinctive transparent dots that can be seen when held up to the light.
Seeds: Are housed in membranous capsules that re 5 – 8 m long. The seeds are dark brown and 1.0 – 1.3 mm long with pitted in longitudinal rows.
Roots: Common St. John’s Wort has a rhizome root system that develops just below the soil surface and can extend over 45 cm.
Habitat and Origin
Common St. John’s Wort is native to Europe, western Asia, and North Africa. It is thought to have been introduced to North America as an ornamental and medicinal herb.
Common St. John’s Wort prefers dry, sandy soil in full sun and can be found in low- to mid-elevation areas on the coast, in grasslands, and forested areas in BC. It can also be seen along roadsides, rail lines, grazing areas, and disturbed sites.
Propagation & Vectors of Spread
Common St. John’s Wort can reproduce via seed production and through its root system. One plant can produce over 100,000 seeds every year, and the seeds can survive in the soil for up to 10 years. The seeds have a gelatinous coating which aids in long-distance dispersal, allowing the seeds to survive harsh conditions. It also aggressively spreads using its lateral root system which forms new buds that are separated from the parent plant.
Common St. John’s Wort spreads aggressively by vegetative reproduction through its root system. Long-distance dispersal occurs through the transport of seeds. The seeds are spread by water, wind, animals, and human activity.
Ecological, Economic, & Health Impacts
- Reduces biodiversity.
- Toxic to livestock.
- Reduces crop quality and quantity.
- Toxic sap causes skin irritation when exposed to the sun.
What Can I Do?
Common St. John’s Wort is found in communities of the Sea to Sky Region, so PREVENTION of further spread is key.
Learn to identify Common St. John’s Wort: use the images presented in this profile page to learn how to identify Common St. John’s Wort.
What to do if you spot it: You can report any Common St. John’s Wort sighting by clicking here.
- Regularly monitor properties for weed infestations.
- Minimize soil disturbances and promptly revegetate disturbed areas to prevent the growth of Common St. John’s Wort.
- Check wildflower mixes to ensure that they do not contain Common St. John’s Wort.
- Ensure all flowering heads or buds are bagged or covered to prevent spread during transport to designated disposal sites.
- Do not unload, park or store equipment or vehicles in infested areas; remove plant material from any equipment, vehicles or clothing used in such areas and wash equipment and vehicles at designated cleaning sites before leaving infested areas.
- Do not plant Common St. John’s Wort in a garden, no matter how well-contained its enclosure may seem.
- Do not move soil, gravel, or fill that has been contaminated with Common St. John’s Wort.
- Do not compost any flowering heads or buds. Instead, dispose of Common St. John’s Wort in the general/household waste stream at the landfill as the seeds will be able to persist the composting process.
- Tillage followed by the sowing of perennial grasses and legumes can potentially be effective. However, removal of the stems by any means (grazing, fire, defoliation) stimulates re-sprouting.
- Hand pulling/digging cannot effectively remove the extensive root system and can also leave roots to re-sprout.
- Several herbicides have been effective against Common St. John’s Wort. Herbicide treatments of 2,4-D, aminopyralid, glyphosate, metsulfuron and picloram are the most effective post emergence and before bloom.
- However, picloram is not suitable for wet, coastal soils.
- We recommend that any herbicide application is carried out by a person holding a valid BC Pesticide Applicator Certificate. Before selecting and applying herbicides, you must review and follow herbicide labels and application rates; municipal, regional, provincial and federal laws and regulations; species-specific treatment recommendations, and site-specific goals and objectives.
- There are numerous biocontrol agents available for Common St. John’s Wort.
- However, plants may continue to spread when treated with biological control agents.
- The most effective are the foliar feeding beetle Chrysolina hyperici, the foliar feeding beetle Chrysolina quadrigemina, and the root feeding beetle Agrilus hyperici.
Alberta Invasive Species Council, St John’s-wort, https://abinvasives.ca/wp-content/uploads/2017/11/FS-StJohnsWort.pdf
Coastal Invasive Species Committee, St. John’s Wort, https://www.coastalisc.com/st-johns-wort/
Invasive Plant Atlas of the US, common St. Johnswort, https://www.invasiveplantatlas.org/subject.html?sub=4411
Invasive Species Council of BC, St John’s Wort, https://bcinvasives.ca/invasive-species/identify/invasive-plants/st-johns-wort
Invasive Species Council of Manitoba, St. John’s Wort, https://invasivespeciesmanitoba.com/site/index.php?page=st-john-s-wort
University of California, Weed Control in Natural Areas in the Western United States, https://wric.ucdavis.edu/information/natural%20areas/wr_H/Hypericum_perforatum.pdf
US Department of Agriculture, St. Johnswort, https://www.invasivespeciesinfo.gov/terrestrial/plants/st-johnswort
Washington State Noxious Weed Control Board, Common St. Johnswort, https://www.nwcb.wa.gov/weeds/common-st-johnswort