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Common St. John's Wort (Hypericum perforatum), whole plant
  • Common St. John's Wort — close-up of leaves and flowers
  • Common St. John's Wort — seasonal appearance
  • Common St. John's Wort in a garden setting

Common St. John's Wort

Hypericum perforatum

Easy · Beginner friendly

About Common St. John's Wort

Hypericum perforatum, St. John's wort, is a sun-loving Eurasian perennial naturalized across much of North America. It carries small opposite leaves dotted with translucent oil glands and bright yellow summer flowers that stain red when crushed. The plant has a long history in European herbalism and modern supplement culture, especially around mood, which is why it deserves caution: its compounds can interact seriously with many medications by altering liver enzyme activity. In gardens and pastures it can self-seed aggressively and may be toxic to grazing livestock. As a plant it is beautiful and historically fascinating; as a supplement, it belongs in the realm of professional guidance rather than casual use.

  • Medicinal
  • Drought-tolerant
  • Cold-hardy
  • Pollinator-friendly
WATER
Low water
Minimal water
LIGHT
Full sun
6+ hrs direct
HARDY
Hardy to -30°F (-34°C)
USDA hardiness zones 4–8

How to care for Common St. John's Wort

Watering

  • Springevery 5 days
  • Summerevery 4 days
  • Fallevery 7 days
  • Winterevery 14 days

Soil · Well-draining

  • Top dressingPine bark mulch10%
  • Main mixPotting soil + perlite 2:170%
  • DrainageLECA / gravel20%

Never skip the drainage layer — standing water is the top cause of root rot.

FERTILIZER

Balanced Feed 14-14-14

An even feed covers all three needs at once, keeping leaves, roots and blooms moving together with nothing pushed out of balance.

N33%P33%K33%
  • Nitrogen · Leaves
  • Phosphorus · Roots + Blooms
  • Potassium · Strength
  • Springevery 45 days
  • Summerevery 45 days
  • Fallevery 60 days
Get watering reminders for Common St. John's Wort — free on iPhoneDownload on the App Store

At a Glance

  • NativeEurope, Africa, Western Asia
  • Height1–3 ft (0.3–0.9 m)
  • Spread1–2 ft (0.3–0.6 m)
  • Flower colorYellow
  • Foliage colorGreen
  • SoilLoamy, Well-drained
  • LocationsYard

Bloom time

BLOOM CYCLE

Peak bloom

Jun–Aug

J
F
M
A
M
J
J
A
S
O
N
D

Flowers peak around the summer solstice; deadhead to prevent invasive self-sowing.

Fragrance

LIGHT FRAGRANCE

The flowers have a mild herbal scent.

Toxicity

Humans Moderate · Pets Moderate

hypericin and hyperforin

Moderate

  • All
  • Ingestion

EXPOSURE Eating any part of the plant.

EFFECT Photosensitivity, severe drug interactions, and serotonin syndrome risk with SSRIs.

NOTE Documented concern for humans: Photosensitivity, severe drug interactions, and serotonin syndrome risk with SSRIs.

Moderate

  • All
  • Ingestion

EXPOSURE Eating any part of the plant.

EFFECT Photosensitivity dermatitis and severe sunburn and depression, vomiting (per ASPCA).

NOTE ASPCA lists Hypericum as toxic to dogs, cats, horses due to hypericin photosensitization. Major drug-interaction hazard in humans.

Moderate

  • All
  • Ingestion

EXPOSURE Eating any part of the plant.

EFFECT Photosensitivity and depression, vomiting.

NOTE ASPCA lists Hypericum as toxic to dogs, cats, horses due to hypericin photosensitization. Major drug-interaction hazard in humans.

Educational information, not medical or veterinary advice. If exposure is suspected, contact a doctor or veterinarian.

DISTRIBUTION

Common St. John's Wort · Native
  • Native
  • Introduced
  • Europe
  • Africa
  • Western Asia

History

Illustrated historical scene for Common St. John's Wort

Hypericum perforatum is native to Europe, North Africa, and western Asia, and has naturalized widely across North America, Australia, and New Zealand. The common name honors St. John the Baptist — the plant typically reaches peak bloom around June 24, the saint's feast day — and in medieval Christian tradition branches were placed over doorways on St. John's Eve to ward off evil. Paracelsus and other Renaissance physicians documented its use for mental melancholy and wounds.

Modern phytochemistry identifies hypericin and hyperforin as primary active constituents; since the 1990s a substantial body of clinical trial evidence (meta-analyses including multiple Cochrane reviews) has supported efficacy comparable to SSRIs for mild-to-moderate depression, with generally fewer side effects. However, St. John's wort is a potent inducer of cytochrome P450 3A4, causing numerous significant drug interactions — notably with contraceptives, HIV medications, immunosuppressants, and warfarin — leading Ireland and some other jurisdictions to require prescription for high-dose standardized extracts. In Australia and North America it is also a serious invasive weed.

Named for St. John the Baptist because it blooms near his feast day. In 1996, the British Medical Journal published a meta-analysis confirming its antidepressant efficacy, triggering a global sales boom. Germany's Commission E approved it for depression in 1984.

Symbolism & meaning

What It Symbolizes

Common St. John's wort is often read as a flower of midsummer light. Golden blooms open near the solstice, and old villages hung the herb around doors when the year felt brightest and spirits most exposed. Its symbolism is radiance with caution: a sun-colored plant whose history is powerful enough to deserve respect.

  • Light — Blooming at the summer solstice and used against melancholy, St. John's wort symbolizes the triumph of light over darkness
  • Protection — Hung over doors on Midsummer's Eve to repel evil spirits and bring blessings

Where the Name Comes From

Hypericum from Greek 'hyper' (above) + 'eikon' (image/icon), as the plant was hung above religious icons to ward off evil; 'perforatum' for the perforated-looking translucent leaf glands.

Uses & Fun Facts

  • Yellow flowers tinctured as traditional remedy for mild depression
  • Pollen-rich blooms attract honeybees and native bee species

Related plants

More Hypericum plants

Plants with similar care

Frequently asked questions

How often should I water Common St. John's Wort?

In summer, water about every 4 days; in winter, about every 14 days. Adjust for heat, pot size and drainage.

How much light does Common St. John's Wort need?

Full sun: 6+ hrs direct. Watch the leaves — scorching or stretching means the light needs adjusting.

Is Common St. John's Wort toxic to cats or dogs?

Pets Moderate (Dogs Moderate · Cats Moderate) Educational information, not medical or veterinary advice. If exposure is suspected, contact a doctor or veterinarian.

Is Common St. John's Wort easy to grow?

Yes — it is considered an easy, beginner-friendly plant.

When does Common St. John's Wort bloom?

It typically blooms Jun–Aug in the Northern Hemisphere.

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