St John's Wort – Harvesting, Processing and What to Watch For
St. John's wort (Hypericum perforatum) blooms bright yellow around St. John's Day (June 24th). It's one of the best-researched medicinal plants in Europe. What those studies looked at, though, were standardised extracts in controlled doses – not self-foraged herb, where neither the active compound content nor the amount can be pinned down.
Active Compounds and Their Traditional Uses
St. John's wort contains:
- Hypericin – mood-lifting, antiviral; turns the red oil dark red
- Flavonoids – anti-inflammatory, calming
- Tannins – wound-healing, for external use
Traditional uses: low mood, inner restlessness, sleep problems, nerve pain (external), wounds and burns (external).
⚠️ Interactions – Please Read in Full
St. John's wort is not a harmless little herb: it is the medicinal plant with the most known interactions of all. In the liver it speeds up the breakdown of numerous medications and thereby weakens their effect.
Affected are, among others:
- Hormonal contraceptives – up to and including loss of contraceptive protection
- Anticoagulants (e.g. Marcumar/warfarin)
- Immunosuppressants
- Certain HIV, cancer and heart medications
- Antidepressants – here it works the other way round: combined with serotonin reuptake inhibitors (e.g. sertraline, paroxetine), it can very rarely cause serotonin syndrome according to the EMA (including sweating, racing heart, fever, agitation, tremor)
St. John's wort can also make the skin more sensitive to light. When taking it internally, avoid intense sun exposure and tanning beds – especially with fair skin.
If you take medication regularly, do not use St. John's wort without talking to your doctor or pharmacist first.
Depression Belongs in Medical Care
Depression is a serious illness and belongs in medical care – St. John's wort is no substitute for that. The same goes for low mood, restlessness or sleep problems that last: get them looked at rather than treating them on your own.
What to Look For
Two features are typical:
- Rub a petal between your fingers – it turns dark red to violet. That's the hypericin.
- Hold a leaf up to the light – it shows light dots (oil glands) and sometimes dark dots along the edges.
Both features together point to St. John's wort. Even so, always check several features and take your time: the same dry, sunny sites are home to yellow-flowering ragwort, which contains liver-toxic pyrrolizidine alkaloids and has no place in tea or oil. Anything you can't place, leave standing.
When & How to Harvest
Best harvest time: June to August, around St. John's Day – when the plant is just coming into bloom and still carries buds. That's when the active compound content is highest.
What to harvest: The top 10–15 cm with flowers, buds, and leaves. Only from plants at dry, sunny sites – roadsides, embankments, poor grassland.
Do not forage: On fertilized meadows, roadsides, or shady damp spots.
Making St. John's Wort Oil Yourself – the Classic
Red St. John's wort oil takes little effort to make yourself.
Preparation:
- Put freshly harvested flowers and buds into a clean jar (don't dry them – use fresh!)
- Cover with high-quality olive oil or almond oil, all plant parts must be under the oil
- Seal the jar and let it sit 4–6 weeks on a sunny windowsill – shake gently every day
- The oil slowly turns dark red – that's a good sign
- Strain, fill into dark bottles
Shelf life: 1–2 years stored cool and dark.
Traditionally used: externally for muscle tension, nerve pain, bruises, minor burns, and scars. Not on facial wounds before sun exposure.
Internal Use
Tea – 1–2 tsp dried flowers and leaves, steep covered for 10 minutes.
Tincture – steep fresh flowers in 40–50% alcohol for 4–6 weeks, then strain.
Drying & Preserving
Dry flowers and leaves spread loosely at max. 40°C – don't layer too thickly, they mold easily. Store dark and dry.
Shelf life: 1 year. After that, the dried herb loses significant potency.
Sources
- European Medicines Agency (EMA): European Union herbal monograph on Hypericum perforatum L., herba (Revision 1), as of 23 Nov 2022, accessed 5 Oct 2026
The sources support individual statements in this article. The organisations named have neither reviewed nor endorsed it.