St. John’s Wort

St. John’s Wort

Fact Sheet


Latin Name: Hypericum perforatum 

Origin:  Eurasia

Physical Description: it is a perennial herb from a rhizome. Reddish stems are erect, highly branched and grow up to 1m tall. Leaves are yellow-green in colour, 5-3 cm long, and 1.5-5 mm wide, elliptic or linear, with rounded bases, and smooth margins. Flowers are bright yellow with 5 petals, and have pronounced stamens in the center.

Habitat: it inhabits a wide range of dry to moist environments, and prefers gravel or sandy soils. It can commonly be found growing in grasslands, pastures, rangeland, waste areas, roadsides, and other disturbed areas.

Impacts: it is toxic and if consumed in sufficient quantities, can cause photosensitivity, loss of weigh and, in rare cases, death, in grazers. It also out-competes native plants, reducing biodiversity.

Reproduction: it reproduces by seed and by vegetative growth. One plant can produce up to 33,000 seeds that can remain viable in the soil for up to 10 years. It also reproduces vegetatively by rhizomes, root fragments or lateral root sprouts.

Management Options

Mechanical: hand pulling or digging small populations can be effective as long as the entire taproot and all underground runners are removed. Mowing is not recommended because plants can re-sprout rom underground root reserves. Tilling is also effective in crops.

Chemical: Several herbicides with the following active ingredients can control St. John’s Wort: glyphosate, 2,4-D, aminopyralid, picloram, and metsulfuron.  For available products, contact your local agri-supply store. Prior to any herbicide application, read and follow the label instructions.

Biological: Several biological control agents are available either in mass or limited distribution:

Additional Resources:

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