Hypericum perforatum
Midwest Noxious Weed: Do Not Plant

Common Name: common St. John's wort 
Type: Herbaceous perennial
Family: Hypericaceae
Native Range: Europe to central China, northern Africa, western Himalyans
Zone: 3 to 8
Height: 1.00 to 3.00 feet
Spread: 0.75 to 2.00 feet
Bloom Time: June to August
Bloom Description: Yellow
Sun: Full sun to part shade
Water: Medium
Maintenance: Low
Suggested Use: Naturalize
Flower: Showy
Tolerate: Drought
This plant is listed as a noxious weed in one or more Midwestern states outside Missouri and should not be moved or grown under conditions that would involve danger of dissemination.

Culture

Easily grown in medium moisture, well-drained soils in full sun to part shade. Species plants prefer sandy or gravelly soils in sunny areas. They tolerate some drought once established. They develop extensive root systems, and spread by both runners and often prolific self-seeding. A single plant may produce up to 100,000 seeds per year. Seeds buried in soil may last for 10 years. Species plants are listed as noxious weeds in California, Colorado, Montana, Nevada, Oregon, South Dakota, Washington, Wisconsin and Wyoming.

Noteworthy Characteristics

Hypericum perforatum, St. John’s wort (sometimes commonly called perforate St. John's wort, goatweed or Klamath weed) is an upright, many-branched, stoloniferous, yellow-flowered, herbaceous perennial (some say perennial weed) that is native to Europe, western Asia and northern Africa. Plants were first brought to North America by settlers in 1696, and have naturalized over time throughout much of the continent. In Missouri, this species is now found in scattered locations throughout the State primarily in fields, waste ground, pastures, railroad right-of-ways and along roads (Steyermark). It typically grows from a woody, branched rootstock to 1-3’ tall, and features a showy display of star-shaped, yellow flowers (1 1/2” diameter) that bloom in pyramidal compound cymes in summer (June-August). Each flower has 5 yellow petals peppered with black dots, a pistil with 3 styles and a center boss of bushy yellow stamens. Stem-clasping, elliptic to oblong leaves to (1 1/4” long) have translucent dots and black marginal punctations. Foliage has an unpleasant aroma when bruised or rubbed.

Since ancient times, hypericum plants have been used as herbal treatments for a variety of medical problems including externally for wounds, inflammations, burns, skin disorders, and nerve pain and internally for anxiety, depression and insomnia. The flowers were at one point gathered and displayed to ward off evil spirits. Flowers are typically in bloom on the birthday of St. John the Baptist (June 24). Wort is a name often given to a healing plant. The active ingredient in the leaves and flowers is hypercin.

Genus name comes from the Greek words hyper meaning above and eikon meaning picture in reference to the practice of hanging flowers from this genus above images, pictures or windows.

Specific epithet is in reference to the perforated appearance of the leaves (from the translucent dots).

Additional common names include goatweed or Klamath weed (plant was first discovered growing in the wild in California near the Klamath River).

Problems

No serious insect or disease problems. Invasive spread can displace native species.

Garden Uses

Borders, woodland margins or slopes. Naturalized areas. Wild gardens. Medows. Herb gardens.