St. John's Wort Plant Profile

St John's Wort

The Spruce / Adrienne Legault

Common St. John's wort was so valued for its medicinal qualities in its native Europe that settlers brought it over with them to the New World. But if you are not interested in herbalism, you will probably find greater value in relatives of the same genus. These types of St. John's wort are known for features such as showy berries and two-toned foliage.

Botanical Name Hypericum perforatum
Common Name Common St. John's wort, Klamath weed, goatweed, tipton weed, devil's scourge, rosin weed, god's wonder plant, perforate St. John's wort
Plant Type Herbaceous plant with a perennial life cycle
Mature Size 1 to 3 feet tall and not quite as wide; upright growing habit
Sun Exposure Full sun to partial shade
Soil Type Rich, well-drained, with average moisture content
Soil pH Acidic, neutral, or alkaline
Bloom Time June through September
Flower Color Yellow
Hardiness Zones 3 to 8
Native Area Europe, Asia, and North Africa; has naturalized in North America
closeup of St John's Wort
The Spruce / Adrienne Legault 
St. John's Wort used as a groundcover
The Spruce / Adrienne Legault

Origin of the Names

The primary common name (alternate spellings, "St. Johnswort" and "St. John's-wort") refers to the fact that the flowers were traditionally harvested on the Catholic Saint's Day honoring the nativity of St. John the Baptist, June 24. After harvesting the flowers, the believer would hang them over a painting or statue of St. John in the home. This practice was thought to protect the believer from evil spirits. The word, "wort" (most often found as a suffix) is simply Old English for "plant" and is frequently found in common plant names, other examples being:

The genus name refers to the same religious practice. Hypericum is made up of two Greek words: hyper (above) and eikon (image). The species name of perforatum refers to the see-through (when held up against the light) dots on the leaves that give them a "perforated" appearance.

How to Grow St. John's Wort

St. John's wort is an easy plant to grow, being tolerant of a number of challenging conditions. Thus its status as a weed in the opinion of many gardeners. If it has any Achilles heel at all, it is an overly wet soil. You may have to baby young plants for a while, but, once established, St. John's wort will survive on its own. In fact, your main maintenance chore with established plants will be keeping them in check.

Light

Grow St. John's wort in full sun in the North for best flower production. In the South, however, the plant profits from having a bit of shade.

Soil

Although the plant prefers a well-drained soil, it will tolerate compacted ground.

Water

Keep this perennial well-irrigated when you are first trying to establish it. Once mature, it is reasonably drought-tolerant.

Fertilizer

St. John's wort performs best in fertile soils, although it tolerates poor soils. Amend its soil with compost annually for best results.

Medicinal, Toxic, and Invasive Nature of St. John's Wort

St. John's wort has been used medicinally in many ways over the centuries, including:

  • For kidney ailments, insomnia
  • As an antidepressant
  • For lung ailments
  • As a vulnerary (herb that promote the healing of wounds)
  • For insomnia

But the plant does have its drawbacks. When taken as a medicine, it does have side effects, such headache, dizziness, and nausea. If eaten in sufficient quantities, it is poisonous to livestock. It is hard to contain this perennial, since it spreads in two ways:

This helps account for why it is considered an invasive plant in some regions. Deadheading will stop the plant from going to seed, while the spread of the stolons can be stopped by installing barriers, as you would for bamboo control.

St. John's Wort as an Ornamental

Although more famous as a medicinal plant, St. John's wort does have some ornamental features. Its flowers are not only a bright yellow color, but they also sport showy stamens (the long, slender flower parts that carry pollen). Nonetheless, Hypericum perforatum is not the most ornamental member of its genus for use in the landscape. The Hypericum genus has cultivars and shrubby species that are prettier, including:

  • Hypericum x inodorum 'Elstead': zones 6 to 9; 4 feet tall, 5 feet wide; red berries
  • Hypericum x moserianum 'Tricolor': zones 6 to 9; 1 to 2.5 feet tall, with a slightly greater spread; variegated leaves (green, pink, and creamy-white)
Hypericum x inodorum