St. John's Wort

Hypericum perforatum

herb

St. John's wort (Hypericum perforatum) is a wiry, upright perennial, 1 to 3 ft tall, that bursts into bright golden-yellow, five-petaled flowers around midsummer - traditionally around St. John's Day, hence the name. Hold a leaf to the light and you see tiny translucent dots (the perforatum of its name), and the flowers and buds yield a deep red pigment when crushed. It is among the most famous of traditional herbs, harvested as the flowering tops, and a tough, drought-hardy, sun-loving plant. But it spreads vigorously by runners and prolific seed and is toxic to grazing livestock, so it is a listed noxious weed across much of the western US, where it should not be planted.

✅ Plant alongside

Good neighbors that attract beneficial insects or deter pests

• Yarrow — A drought-hardy companion that draws beneficial insects to the same lean, sunny bed
• Purple Coneflower — Shares the full-sun, well-drained conditions and extends the pollinator season

🛡️ Pest & disease prevention

Proactive ways to stop trouble before it starts — tap a name with an arrow for its full guide

• Aphids →

  Hose colonies from the growth; predators usually follow

• Root rot →

  Plant in well-drained soil and avoid waterlogging

• Spreading

  The real management issue - deadhead before seed sets and dig out runners to keep it from colonizing

🌾 Harvest & storage

Harvest the flowering tops at peak bloom around midsummer, when the buds and open flowers are most abundant - the unopened buds and fresh flowers are richest in the red pigment. Cut the top few inches of the flowering stems on a dry morning and dry them in a shaded, airy place, or infuse the fresh flowers in oil, which turns a deep ruby red. Pick over the bloom season, and cut before heavy seed set to limit spread.

🥗 Nutrition & benefits

St. John's wort is grown strictly as a traditional herb, not a food - the flowering tops are dried for tea and tincture or infused in oil (the well-known red oil) in a long folk tradition. Note that it is not eaten as a vegetable, it can make skin more sensitive to sunlight, and it is a regulated noxious weed in several western states, so check local rules before planting it.

⚠️ Toxicity & safety

Use with caution - serious drug interactions. St. John's Wort interferes with many medications, including birth control pills (risk of unintended pregnancy), antidepressants (risk of dangerous serotonin build-up), blood thinners, and more, and it can make skin more sensitive to sunlight. Talk to a doctor or pharmacist before using it if you take any medication.