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St. John’s Wort (Hypericum perforatum)

SWCD Branded Separator

Also known as: St. Johnswort, common St. John’s wort, goatweed, klamath weed, tipton weed

St. John’s wort is found all over the world. It is toxic to livestock, causing livestock’s skin to become hypersensitive to sunlight. A single plant can produce 100,000 small seeds per year which allows it to spread quickly and makes it difficult to control.

Description:

Life Cycle:Perennial (life cycle lasts more than one year)
Early Detection and Rapid Response species:No
Height:Up to 2 feet (0.6 meters)
Leaf Description:Oblong, deep green leaves have small translucent dots that can be seen when held up a light source. They grow opposite along the stem.
Fruit & Flower Description:Bright yellow flowers grow in clusters at the top of the plant. Each flower has five petals with black dots along their edges.

A single plant can produce 100,000 small, black seeds annually. Seeds can remain viable in the soil for 10 years or more.
Bloom Time:June to July

Habitat:

  • St. John’s wort is a sun-loving plant which grows in well-drained soils.
  • It is commonly found in pastures, meadows, roadsides, recently logged areas, and along trails.

Impact:

  • It is toxic to livestock. Overexposure can cause severe skin lesions and make livestock’s skin become hypersensitive to sunlight.
  • It outcompetes native plants, crops, and forage for resources.

What you can do about it:

  • Removing St. John’s wort after seeds have been produced is not recommended. This will spread its seeds to new areas.
  • Small patches can be removed by hand or with hand tools. Pay close attention to removing as much of the root as possible. Place all plant material in a tied plastic bag and dispose of in the trash – not in the yard debris or home compost.
  • Tilling is an effective control for large patches.
  • Seeding an area after any treatment is critical to long-term suppression of this weed. Without competition, it will quickly regrow.

Look-alikes:

St. John’s wort is often confused with tansy ragwort (Jacobaea vulgaris) and common tansy (Tanacetum vulgare). Unlike tansy ragwort and common tansy, St. John’s wort’s flowers have five petals.

Noxious Weed Listing:

State of Oregon:Class B
State of Washington:Class C

More Resources:

Download St. John’s Wort Best Management Practices factsheet

Download Factsheet