St. John’s wort
Also known as
Common St. John’s wort, Perforate St. John’s-wort, Klamath weed, Goatweed
Keep this plant’s care guide close at hand.
Get the appAbout St. John’s wort
Hypericum perforatum is a hardy, rhizomatous perennial herb prized for its bright, starry yellow blooms and dotted, translucent leaves that appear “perforated” when held to the light. Plants typically reach 30–90 cm tall, with opposite, narrow leaves and clusters of five-petaled flowers bearing numerous prominent stamens from late spring through summer. Native to Europe and parts of Western Asia and North Africa, it has naturalized widely and can become invasive in disturbed sites. It thrives in well-drained, low-fertility soils and full sun, tolerating drought once established. Historically, it has been used as an herbal remedy, though it can interact with medications and cause photosensitivity. In gardens or containers, it is valued for resilience, pollinator support, and long bloom. Control spread by deadheading and limiting root expansion. Provide sharp drainage to avoid winter wet, and prune annually to maintain compact growth. In containers, occasional light feeding and periodic division keep plants vigorous.
Taxonomy
Properties & Requirements
How to care for St. John’s wort
Water
Keep evenly moist during the first growing season to establish a deep root system. Thereafter, water deeply but infrequently, allowing the top 3–5 cm of soil to dry between waterings. In containers, water when the top inch is dry and ensure excellent drainage; never let the pot sit in a saucer of water. Reduce watering significantly in winter dormancy, especially outdoors. Overwatering and poor drainage are the main causes of decline, promoting root rot and weak, sappy growth.
Light
Full sun (6+ hours direct light) produces the best flowering and compact growth. In very hot regions, provide light afternoon shade to reduce stress and leaf scorch. It will tolerate light shade, but expect fewer flowers and leggier stems. Indoor or balcony culture requires the brightest possible exposure—south or west-facing—with supplemental grow lights if needed in winter. Avoid deep shade and low-light corners, which promote weak growth and sparse blooms.
Nutrients
Hypericum perforatum prefers lean soils and generally needs little to no fertilizer in the ground. For container-grown plants, use a balanced, low-strength, slow-release fertilizer or a half-strength liquid feed (e.g., 5-5-5 to 10-10-10) once monthly from spring to midsummer, then stop. Avoid high-nitrogen formulas that encourage lush, floppy growth over flowers. Flush containers with plain water occasionally to prevent salt buildup, and refresh potting mix or top-dress with compost annually rather than overfeeding.
Temperature
Best growth occurs in cool to warm conditions around 15–25°C (59–77°F). Once established in the ground, it is cold-hardy to roughly USDA Zones 4–9, tolerating winter lows near −30°C (−22°F) if soil drains well. Prolonged heat above 32°C (90°F) may reduce flowering; provide afternoon shade and consistent moisture in hot climates. Container plants are less cold-hardy: protect roots from hard freezes and avoid waterlogged media in winter. Good air flow helps prevent foliar diseases.
