St. John’s Wort (Hypericum perforatum L.)

This plant is a perennial forb that grows up to 1 metre high. It has bright yellow flowers in flat-topped clusters. The leaves are oval-shaped covered in transparent dots and has prominent veins. It reproduces by seed and vegetatively from roots. Each plant can produce between 15 and 30,000 seeds. It flowers from June to September.


Habitat & Ecology

It grows a variety of environments including open forests, grasslands, coastal and low to mid elevations. It grows the best in dry gravelly or sandy soils.


St. John’s Wort can displace native species especially in disturbed areas. It can reduce forage for both livestock and wildlife. It has a toxin that can cause skin irritation in some livestock when they are exposed to sunlight.


Infestations can be managed in pastures with tillage. It is best to maintain healthy plant communities that contain perennial grasses and forbs. There are 5 biocontrol agents that have been released on infestations. There are 3 beetles, a moth and an aphid that are the natural enemy of this plant. Please contact LRISS for more information on management.


Province of British Columbia. 2002. A Guide to Weeds in British Columbia.