St. John's Wort
Hypericum perforatum
St. John's wort is a hardy yellow-flowered perennial famed as a traditional remedy for low mood. Tough and drought-tolerant, it is also a noxious weed in many grazing regions.
- Light
- Full sun
- Water
- Low to moderate; drought-tolerant
- Difficulty
- Easy
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Overview
St. John's wort is a hardy, upright perennial in the family Hypericaceae, producing masses of bright yellow, five-petaled flowers in summer. It is best known as a herbal remedy for mild depression and anxiety, with extracts widely sold as supplements.
The name refers to its traditional flowering around St. John's Day (24 June). The species epithet perforatum describes the translucent oil glands that dot the leaves, looking like tiny perforations when held to the light. It is a tough plant that has become an invasive weed of rangeland in parts of North America and Australia.
How to identify it
- Leaves: Small, oval, stalkless, opposite; held to the light they show translucent dots (oil glands), a key diagnostic feature
- Flowers: Bright yellow, five-petaled, about 2 cm across, with many stamens and black dots along the petal edges
- Habit: Erect, branching perennial 30-90 cm tall
- Stems: Two raised ridges run lengthwise along the stem
- Sap: Crushed flower buds release a reddish pigment (hypericin)
Care & growing
- Light: Full sun for best flowering
- Water: Low to moderate; well established plants are drought-tolerant
- Soil: Tolerant of poor, dry, well-drained soils
- Temperature: Very hardy, roughly zones 3-8
- Feeding: Rarely needed; thrives on lean ground
- Propagation: From seed, division or cuttings; can self-seed and spread readily, so site it carefully or grow ornamental Hypericum cultivars instead
Habitat & origin
St. John's wort is native to Europe, western Asia and North Africa, growing in dry meadows, roadsides, pastures and disturbed ground. It has spread widely and is now naturalized across North America, Australia and elsewhere.
In many grazing regions it is classed as a noxious weed because it crowds out pasture and is toxic to livestock; biological control insects have been used to manage it. It is also cultivated commercially for the herbal supplement trade.
Uses & benefits
The flowering tops are used to make supplements, teas, tinctures and infused oils traditionally taken for mild to moderate depression, anxiety and nerve pain, and applied topically for minor wounds and burns.
Important caution: St. John's wort interacts with many medications (including antidepressants, birth control pills, blood thinners and others) by speeding their breakdown, and can cause photosensitivity. It should not be combined with other drugs without medical advice. In livestock it can cause sun sensitivity and is considered toxic.
Frequently asked questions
Does St. John's wort really help depression?
Several studies suggest standardized extracts can help with mild to moderate depression, but it is not a substitute for medical care and carries serious drug interactions.
What medications does it interact with?
Many, including antidepressants, oral contraceptives, blood thinners, immunosuppressants and HIV drugs. Always consult a doctor or pharmacist before using it.
How can I identify true St. John's wort?
Hold a leaf to the light to see the translucent dots, look for bright yellow five-petaled flowers with black-dotted edges, and note the two ridges on the stem.
Why is it considered a weed?
It spreads aggressively in pastures and rangeland, displaces forage and is toxic to grazing animals, causing photosensitivity, so it is a regulated noxious weed in many areas.
St. John's Wort guides
In-depth guides for identifying, growing, and caring for St. John's Wort.
