St. Johns Wort Plant: Growing Devil’s Scourge

The St Johns wort plant is a useful garden shrub providing multi-season visual interest in garden design, especially from early summer to fall when its bright yellow flowers bring cheeriness to a shady corner.  St. John’s wort may be one of the most adaptive plants you will come across in horticulture, growing well in most types of soil and exposed locations, even tolerating drought conditions.  Once established, this pretty plant will look after itself, but don’t be fooled by its unassuming nature! St. John’s wort can become a bit of a thug in the garden if not managed.

Many folklores and traditions are associated with the St. John’s wort, Hypericum perforatum.  The name Hypericum comes from the Greek hyper meaning above and eikon meaning image and originates from the plant’s use to adorn houses around the feast day of St. John the Baptist, celebrated on 24^th June.  The yellow flowers of Hypericum perforatum were placed above images of the saint to help ward off evil spirits and even death itself.  Perforatum comes from the translucent dots on the leaves visible when held up to the light.

Other folklore beliefs include grinding the flower buds and leaves of Hypericum perforatum to secrete a red juice believed to heal cuts and wounds. Young girls throughout Europe wore a flower around their necks as a love charm. Today the many species and cultivars of St. John’s wort are used in gardening as a ground cover and shade tolerant plant. In modern times the plant is used medicinally in integrative health to treat melancholy, anxiety, mild to moderate depression, and nerve pain. Still, as with all traditional medicines, it is best to consult a doctor before use.

Quick Care Guide

All About St. John’s Wort

The botanical name for St. John’s wort is Hypericum perforatum.  The common names in addition to ‘St. John’s wort’ are extensive and reflect the folklore traditions of this plant.  They include common St. John’s wort, perforate St John’s-wort, herb John, devil chaser, devil’s flight, devil’s scourge, God’s wonder plant, penny John, Klamath weed, rosin rose, and goat weed.

There are over 400 varieties of the Hypericum genus in the Hypericaceae family of plants, originating in Europe, southwestern Asia, and North Africa. It has naturalized in North America, Nova Scotia, and Australia. Hypericum perforatum is the true St. John’s wort in the genus Hypericum and is a small to medium-sized herbaceous shrub with yellow flowers, growing to 1.5-3ft (50-100cms) in height and around 1.5ft (50cm) across. 

Plants have red/brown upright ribbed stems with small, ovate deciduous blue-green foliage with translucent dots, growing in opposite pairs to around 1.25 inches (3cm) long.  New leaves sprout in yellow-green clusters. Flowers grow in abundance and are star-shaped, five-petalled, yellow, and up to 1inch (2.5cm) across.  The fruit consist of small, grooved dark red berries or seed capsules containing tiny brown/black seeds.  

Although St. John’s wort is a relatively small shrub, it can develop extensive rhizomatic root systems which are difficult to remove from the garden once established.  Plants also self-seed, adding to maintenance issues – which is why in some countries, the plants are classified as noxious weeds.  

Planting St. John’s Wort

Grow St. John’s wort plants from seed, cuttings, or shop-bought plants and transplants.  Sow Perforate St John’s wort seeds indoors 6-8 weeks before the last frost for planting out when all risk of frost has passed.  As fully hardy shrubs, mature St. John’s wort plants can be planted at any time of the year except when the ground is frozen. 

To help plants establish quickly and to reduce the risk of frost damage to roots, plant from early spring to fall.  Transplants produced from seed or cuttings taken in mid to late summer should be planted out when strong roots have developed.

Hypericum perforatum plants will adapt to almost any location and soil type in the garden but perform best in full sun to partial shade in fertile, well-drained soil.  Plants will do well in containers with lots of good quality compost added but may need to be watered more frequently.  St. John’s wort makes lovely shrub borders and works well in wildlife and naturalistic rock gardens, along pathways, and in shaded spots where most other plants won’t thrive. The added bonus of its deer-resistant nature means they are seldom severely damaged. You can grow St. John’s Wort almost anywhere. 

There are other species to choose from too, like creeping St. John’s Wort plants (Hypericum calycinum) that work well as ground cover. Or, try Hypericum kalmianum, the bushier version.

To plant Hypericum in the garden, simply dig a hole double the size of the root ball or a container at least 1ft (30cm) in diameter and fill with lots of fresh organic compost to add nutrients and improve moisture retention.  Set the plant into the space, ensuring the stem is at the same level as the ground surface as in the pot.  

Hypericum Perforatum Care

St. John’s wort is a low-maintenance, extremely adaptable plant to grow in your own garden.  Once established, it requires very little aftercare, although a watchful eye is necessary to contain its spread.

Sun and Temperature

Sun and temperature requirements when growing St. John’s wort are dependent on your location.  Provide partial shade in southern/hot climates during the hottest time of day and grow in full sun in northern/cooler climates.  Generally, St. John’s wort tolerates both full sun and almost full shade. However, plant health will begin to deteriorate when daily temperatures are consistently above 75ºF (24 ºC).  

Similarly, too much shade can stunt plant growth. Grow St. John’s Wort in USDA zones 5-10 for full hardiness. In colder zones, give your plant roots plenty of protection to see if they will perennialize.  Plants will benefit from winter mulch, especially if grown in wet soil.

Water and Humidity

When you grow St. John’s Wort in the garden, keep the soil moist until young plants have established.  St. John’s wort will tolerate periods of drought and will even survive occasional flooding.  Water in the morning or early evening with water directed at the soil.  Regular irrigation is not necessary except during long periods of drought and is not required over winter.

Soil

St. John’s wort will adapt to all garden soil types, sand, silty, clay, loam, acidic or alkaline, and even poor soil and compacted ground, but like the plant prefers best in rich, well-drained soils with average moisture content. If you want to adapt a lighter soil type, provide St. John’s Worts with additions of compost and agricultural sand. Overall, as long as the soil is well-drained, Hypericum shrubs will flower and thrive.

Fertilizing

A good organic mulch in fall and/or spring is enough to keep St. John’s wort plants going throughout the growing season. Fertilize Hypericum shrubs planted in poor soils to help them bloom in summer through fall. 

Pruning

It isn’t necessary to prune when you grow St. John’s wort plants unless they become untidy and need re-shaping.  The yellow flowers develop on old wood so pruning back any new growth in early to mid-spring will provide shape and stimulate growth whilst still ensuring the Hypericum shrubs still flower in June.

Propagation

There are three ways to successfully propagate and grow St. John’s wort.  The first method is to start seed indoors in module cells from early spring for planting outside in the garden after the last frost date.  

Seeds can also be sown directly outside once all risk of frost has passed.  Sow seeds into a drill prepared with lots of fresh compost, pressing them gently to make good contact with the soil and water well.  No need to cover as light exposure helps with germination, which can take 10 to 20 days.  Thin seedlings to 1ft (30cms). Hypericum seeds can also be sown in fall for transplanting the following spring.

Take softwood cuttings from new, non-flower growth in July/August.  Cut 4ins (10cms) of the stem just above a leaf bud and remove the lower leaves.  Dip the cut end into some rooting hormone and stick the stem cutting into a pot filled with a mix of compost and perlite.  When roots have formed in a few weeks’ time it is ready to go into the garden.

St. John’s wort can also be propagated by division in spring or fall.  Carefully dig around the plant and gently tease the root ball from the ground. Using two forks back-to-back or a sharp knife/saw, divide the root ball in two.  Replant the divisions into their new garden locations or into a pot as soon as possible and water well until established.

Troubleshooting

St. John’s wort looks after itself, sometimes too well, which is when it can become a problem.  On a positive note, Hypericum plants are rarely affected by pests or diseases. 

Growing Problems

St. John’s wort is a very hardy and extremely adaptable shrub that can tolerate most growing environments making it a great shrub to grow in difficult soils and conditions.  However, its tendency to bloom flowers, self-seed, and spread through the garden via its extensive rhizome root system has resulted in it being classified as a noxious weed/invasive species by many countries worldwide.  St. John’s wort left to its own devices may render land non-viable for other crops.  The rhizomes can be difficult to remove once plants take hold, so it’s important to keep on top of plant maintenance. Rhizomes can lie dormant in the ground for years before making an appearance. 

It’s not all negative news! St. John’s wort is easily managed to reduce the risk of plants becoming invasive.  Simply remove new seedlings as they pop up and before they become established, and prune seed heads when flowers have finished.

Pests

There are no persistent garden pests that affect the growth of this plant.

Disease

In addition to having few pests, Hypericum perforatum is relatively disease resistant also.

Frequently Asked Questions

Q: Is the plant St. John’s wort poisonous?

A: Common St. John’s wort flower is used as a dietary supplement for the treatment of anxiety disorders. However, it is important that a medical doctor is consulted before the consumption of herbal medicines.  Misuse and side effects include diarrhea, dizziness, and skin disorders, and it may interfere with the action of other medications.  

The St. John’s wort plant contains a toxin called hypericin which can be dangerous and, in some cases, fatal to dogs, goats, horses, and sheep.  Symptoms include weight loss, photosensitized skin irritations, and generally poor health.

Q: Is St. Johns wort easy to grow?

A: Once established, St. John’s wort is very easy to grow. It spreads via berries that develop after each flower fades.

Q: Is St. John’s wort a perennial?

A: The St. John’s wort plant is a deciduous perennial herb shrub, meaning it loses it leaves in fall/winter to regrow in spring.

Q: Is St. John’s wort the same as basil?

A: Sweet basil is sometimes referred to as St. John’s wort in a few English-speaking countries, although not in the US. However, the two plants originate from completely different families.  Sweet basil is a highly aromatic leafy annual herb from the mint family, Lamiaceae, and common St. John’s wort is a perennial shrub from the family Hypericaceae.

Q: What happens if a dog eats St. John’s wort?

A: Dogs may be prescribed St. John’s wort herbal remedies for the treatment of anxiety or separation disorder which should be managed by your dog’s veterinarian.  A dog that has accidentally ingested the vegetative St. John’s wort plant may become unwell and develop photosensitized skin irritations.  Seek medical advice if you have any concerns.

Q: Is St. John’s wort evergreen?

A: Common St. John’s wort, Hypericum perforatum, is a deciduous shrub, losing its leaves in fall/winter.  There are lots of ornamental cultivars of St. John’s wort that are evergreen, such as Hypericum frondosum ‘Sunburst’, which has attractive winter berries as well as evergreen foliage.

Q: Does St. John’s wort have berries?

A: Common St. John’s wort, Hypericum perforatum, produces small deep red oval berries after flowering.