St John’s wort (common) Hypericum perforatum
St John’s wort (common) (Hypericum perforatum) is an evergreen perennial herb in the Hypericaceae family, native to Europe, western Asia and North Africa. It grows 30–90 cm (12–35 in) tall and 30–60 cm (12–24 in) wide, wants full sun and low water, and is hardy to about -30 °C (-22 °F). Space plants about 40 cm (16 in) apart.
Plan St John’s wort (common) in your garden →
Free. Draw your beds, then watch it grow through the year in 2D and 3D.
St John’s wort (common) at a glance
| Type | Perennial herb, evergreen |
|---|---|
| Family | Hypericaceae |
| Mature height | 30–90 cm (12–35 in) |
| Mature spread | 30–60 cm (12–24 in) |
| Spacing | 40 cm (16 in) centre to centre |
| Sun | Full sun, at least 6 h of direct sun a day |
| Water | Low; drought tolerance moderate, waterlogging tolerance none |
| Soil pH | 5.5–8 |
| Cold hardiness | About -30 °C (-22 °F) once established (roughly USDA zone 4) |
| Heat stress | Likely above about 34 °C (93 °F) |
| Flowering | from about June for 4–9 weeks (northern hemisphere; later in cold climates, earlier in warm ones) |
| Wind tolerance | Low |
| Pollinator value | Moderate |
| Edible | Not grown as food |
| Native to | Europe, western Asia and North Africa |
| Common in gardens of | 🇩🇪 Germany, 🇬🇧 United Kingdom, 🇫🇷 France, 🇵🇱 Poland, 🇷🇺 Russia, 🇺🇸 United States, 🇹🇷 Turkey, 🇮🇹 Italy |
| Invasive in | western USA and Canada (Klamath weed), Australia, New Zealand, South Africa, Chile, Argentina: check local rules before planting |
Is St John’s wort (common) toxic?
- People: moderately toxic
- Cats: mildly toxic
- Dogs: mildly toxic
- Parts: all parts
Hypericin causes sunburn-like photosensitivity in grazing animals; the ASPCA lists it for cats and dogs. As a medicine it interacts dangerously with many drugs (the contraceptive pill, anticoagulants, antidepressants, transplant drugs).
If a child or pet may have eaten part of a plant, call a poison centre or vet straight away.
Companion planting: what to grow with St John’s wort (common)
No well-documented helpful pairing. Group it with plants that like full sun and low water.
Questions about St John’s wort (common)
- How far apart should I plant St John’s wort (common)?
- About 40 cm (16 in) apart, centre to centre. A mature plant spreads 30–60 cm (12–24 in).
- Does St John’s wort (common) need full sun?
- Full sun: at least 6 hours of direct sun a day.
- How much water does St John’s wort (common) need?
- Low water. Drought tolerance is moderate and waterlogging tolerance none.
- How cold-hardy is St John’s wort (common)?
- It tolerates about -30 °C (-22 °F) once established, roughly USDA zone 4.
- When does St John’s wort (common) flower?
- From about June for 4–9 weeks (northern hemisphere; later in cold climates, earlier in warm ones).
- Is St John’s wort (common) poisonous to cats and dogs?
- For cats it is mildly toxic; for dogs mildly toxic; for people moderately toxic. Hypericin causes sunburn-like photosensitivity in grazing animals; the ASPCA lists it for cats and dogs. As a medicine it interacts dangerously with many drugs (the contraceptive pill, anticoagulants, antidepressants, transplant drugs).
- What grows well with St John’s wort (common)?
- There is no well-documented companion pairing for St John’s wort (common). Group it with plants that like the same sun (full sun) and water (low).
Sources and evidence
Evidence grade A (A: strong evidence).
- Plants of the World Online (taxonomy, native range), Royal Botanic Gardens, Kew
- CABI Invasive Species Compendium, CABI
- Herbal monographs (European Union herbal monographs and assessment reports), European Medicines Agency, Committee on Herbal Medicinal Products
Notes and assumptions
- Hold a leaf to the light to see the translucent oil dots ("perforatum"). Flowers around St John’s Day (24 June). Spreads by seed and runners; beetles (Chrysolina) were released in California and Australia to control it.
Reference values for planning, not horticultural, veterinary or medical advice. Varieties, soils and local climates differ: check with a local nursery or extension service.
Related plants
- Tiew (pink mempat, phak tiu) Cratoxylum formosum
- Basil Ocimum basilicum
- Rosemary Salvia rosmarinus
- Thyme Thymus vulgaris
- Mint Mentha spicata
- Parsley Petroselinum crispum
- Coriander (cilantro) Coriandrum sativum
- Dill Anethum graveolens