Common St. Johnswort
Hypericum perforatum
Common St. Johnswort, known for its bright yellow flowers, is a hardy perennial native to Europe and North America. It is valued for its medicinal properties and vibrant blooms, making it a popular choice in gardens.
Everything it needs
9 essentials at a glance
Watering
Common St.
Johnswort prefers well-drained soil and should be watered when the top inch of soil feels dry. During the growing season (spring and summer), water every 1-2 weeks, adjusting frequency based on rainfall and temperature. In fall and winter, reduce watering to once every 2-3 weeks. Signs of over-watering include yellowing leaves and root rot, while under-watering may cause wilting and leaf drop.
Light
This plant thrives in full sun, requiring at least 6-8 hours of direct sunlight daily.
Ideal placement includes sunny garden beds or borders. It can tolerate partial shade but may not flower as profusely. Avoid placing it in full shade, as this can lead to leggy growth and reduced vigor.
Soil
Common St.
Johnswort prefers sandy or loamy soil with good drainage. The ideal pH range is between 6.0 and 7.0. A potting mix that includes perlite or sand can enhance drainage, preventing root rot.
Humidity
This plant prefers moderate humidity levels but is quite adaptable.
To increase humidity, mist the leaves or place a humidity tray nearby. Signs of low humidity stress include browning leaf tips and wilting. If humidity is too high, it may lead to fungal issues.
Temperature
Common St.
Johnswort thrives in temperatures ranging from 60-75°F (15-24°C). It is hardy in zones 5-9, tolerating cold temperatures down to -20°F (-29°C). In extreme heat, ensure adequate watering to prevent stress.
Fertilizing
Use a balanced fertilizer with an NPK ratio of 10-10-10, applying every 4-6 weeks during the growing season.
In fall, reduce fertilization as the plant enters dormancy. Signs of nutrient deficiency include stunted growth and yellowing leaves.
Pruning
Prune in early spring to remove dead or damaged stems and to shape the plant.
Use sharp, clean pruning shears to make cuts just above a leaf node. Deadheading spent flowers throughout the blooming season encourages more blooms and prevents self-seeding.
Repotting
Repot every 2-3 years or when the plant becomes root-bound.
Signs include roots growing out of the drainage holes or stunted growth. Choose a pot 1-2 inches larger in diameter. Carefully remove the plant from its pot, loosen the roots, and place it in fresh potting mix.
Propagation
Propagation can be achieved through stem cuttings or seeds.
For stem cuttings, take 4-6 inch cuttings in early summer, remove lower leaves, and place them in moist potting mix. Keep the soil consistently moist until roots develop. For seeds, sow in spring or fall, covering lightly with soil and keeping moist until germination.
When it's unhappy
Yellow leaves
Why it happens
Usually caused by over-watering or nutrient deficiency.
How to fix it
Check soil moisture and reduce watering frequency. Fertilize with a balanced fertilizer if nutrient deficiency is suspected.
Wilting
Why it happens
Often due to under-watering or extreme heat.
How to fix it
Increase watering frequency and ensure the plant is in a shaded area during the hottest part of the day.
Root rot
Why it happens
Caused by overly wet soil and poor drainage.
How to fix it
Ensure proper drainage and reduce watering. If root rot is severe, consider repotting into fresh, dry soil.
Fungal infections
Why it happens
High humidity and poor air circulation can lead to fungal issues.
How to fix it
Improve air circulation around the plant and reduce humidity. Use a fungicide if necessary.
Leggy growth
Why it happens
Insufficient light can cause the plant to stretch towards the light source.
How to fix it
Move the plant to a sunnier location to encourage bushier growth.
Care through the year
Spring
In spring, prune back any dead stems and apply a balanced fertilizer to encourage new growth. Monitor for pests as the weather warms.
Summer
During summer, ensure consistent watering, especially in hot weather. Deadhead spent flowers to promote continuous blooming.
Fall
In fall, reduce watering as the plant prepares for dormancy. Consider cutting back the foliage to tidy up the garden.
Winter
In winter, protect the plant from extreme cold by mulching around the base. Water sparingly, only if the soil is dry.
Toxicity & Safety
Common St. Johnswort is generally considered non-toxic to pets and children. However, ingestion of large quantities may cause gastrointestinal upset. The plant can interact with certain medications, so caution is advised.
Good to know
How often should I water my Common St. Johnswort?
Water your Common St. Johnswort every 1-2 weeks during the growing season, allowing the top inch of soil to dry out between waterings.
Why are my St. Johnswort leaves turning yellow?
Yellow leaves can indicate over-watering or nutrient deficiency. Check the soil moisture and consider fertilizing if the soil is dry.
What type of soil is best for Common St. Johnswort?
Common St. Johnswort prefers sandy or loamy soil with good drainage and a pH between 6.0 and 7.0.
Can I grow St. Johnswort indoors?
Yes, St. Johnswort can be grown indoors if provided with adequate sunlight, ideally at least 6-8 hours of direct light each day.
Is Common St. Johnswort invasive?
In some regions, Common St. Johnswort can be invasive. It's best to check local regulations and manage its growth accordingly.
When should I prune my St. Johnswort?
Prune your St. Johnswort in early spring to remove dead stems and shape the plant for better growth.
How do I propagate Common St. Johnswort?
You can propagate Common St. Johnswort through stem cuttings or seeds. For cuttings, take 4-6 inch stems in early summer and root them in moist soil.
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