Invasive Species Council of British Columbia
Invasive Plant

Common St. John’s wort

Hypericum perforatum
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Common St. John’s wort contains a poison that can cause light-coloured farm animals that eat it to have skin burns or blisters when exposed to sunlight.

About This Species

Common St. John’s-Wort is a perennial invasive plant that was introduced as an ornamental and medicinal herb from its native range of Europe, Asia and North Africa. It grows in dense patches which can crowd out natural plants and reduce the grasses that animals feed on. Common St. John’s-Wort spreads by lateral roots and can produce up to 100,000 seeds per plant. 

How to Identify

Common St. John’s wort grows from 0.3–1 m in height. 

It has dark green, opposite leaves which show tiny transparent dots when held up to the light.  

Flowers are bright yellow, with 5 petals each, and grow in clusters at the top of branches. It turns a rusty red colour after finishing flowering late in the summer and autumn. 

Take Action

Hand pulling or digging St. John’s wort before the flowers go to seed can reduce the spread of this plant. Remove as much of the root system as possible to help prevent regrowth.

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