Details and Information

Common Names

 St. John's-wort, Common St. John's-wort, Klamath weeds, tipton weed, perforate St John's-wort,  


St. John's Wort is a perennial that can grow from 1-2 feet in height. This plant has a long taproot and shallow rhizomes which extend from the root crown. The stems are reddish in color and can be single or multiple with two opposite longitudinal ridges and the stems can branch many times towards the tip of the plant. The leaves are lance-shaped, opposite on the stem and 1-2 inches long with smooth margins. Each leaf contains tiny pinpoints of holes which are visible when held up to the light. Flowers are yellow and star-shaped with 5 petals and have tiny black dots that can be found along the edges of the petals. Seeds are in 3 sectioned pods filled with many dark brown seeds and each plant can produce up to 100,000 seeds and will reproduce by the aggressive root system and by the seeds. The blooming occurs in mid-summer and lasts about a month. 

Key Features

The leaves contain tiny pinpoint holes that are visible when held up to the light. Also there are black oil glands along the margins of the yellow petals that are a sure sign it is St. Johnswort. 


St. John's-Wort prefers poor dry, gravelly or sandy soils in full sun. It can be found in right-of-ways, meadows, dry pastures, rangelands, open woods and disturbed areas. 


 There are herbicides and other control methods that commonly control St. John's-Wort. Herbicides include Milestone, Tordon, 2,4-D, Triclopyr, and glyphosate. For more information on these herbicides and other control methods contact the Weed and Pest office. 

Other Facts

Animals will not seek out Common St. John's-wort as it is toxic to livestock when consumed in quantity. In herbal medicine the chemical produced by St. John’s-wort is hypericin, which is the antidepressant ingredient in St. John's-Wort remedies. Hypericin is a photo-reactive pigment that is readily absorbed by the digestive tract and can cause photo-sensitivity.