How to Plant, Grow, and Care for St John’s wort
The yellow, saucer-shaped blooms of St. John's wort are cheery additions to any garden. This medicinal herb is handy addition to the garden. Ann McCarron provides tips for growing it.
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The St John’s wort is a useful garden shrub providing multi-season visual interest in garden design. From early summer to fall, its bright yellow flowers bring cheeriness to a shady corner. It may be one of the most adaptive herbs you will come across in horticulture. It grows well in most types of soil and exposed locations, even tolerating drought conditions. Once established, this pretty herb will look after itself, but don’t be fooled by its unassuming nature! This herb 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. It originates from the use to adorning houses around the feast day of St John the Baptist, celebrated on 24 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 species. In modern times, it 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.
Plant Overview
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Plant
Perennial herb
Family
Hypericaceae
Genus
Hypericum
Species
Hypericum perforatum
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Native Area
Europe, Scandanavia and Eastern Asia
Exposure
Full sun to partial shade
Height
1-3′
Watering Requirements
Low
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Pests & Diseases
None
Maintenance
Low
Soil Type
Well-draining, all types
Hardiness Zone
3-8
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What is St John’s wort?
The botanical name for St John’s wort is Hypericum perforatum. The common names are extensive and reflect the folklore traditions. 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.
Native Area
There are over 400 varieties of the Hypericum genus in the Hypericaceae family. They originate in Europe, southwestern Asia, and North Africa. It has naturalized in North America, Nova Scotia, and Australia, and is classed as invasive in some parts of the world.
Characteristics
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. It grows to one and a half to three feet in height and around one and a half feet across.
They have red/brown upright ribbed stems with small, ovate deciduous blue-green foliage with translucent dots, growing in opposite pairs to around one and a quarter inches long. New leaves sprout in yellow-green clusters. Flowers grow in abundance and are star-shaped, five-petalled, yellow, and up to one inch across. The fruit consists of small, grooved dark red berries or seed capsules containing tiny brown/black seeds.
Although it is a relatively small shrub, it can develop extensive rhizomatic root systems which are difficult to remove from the garden once established. They also self-seed, adding to maintenance issues. This is why in some countries, they are classified as noxious weeds.
Planting
Grow St John’s wort from seed, cuttings, or shop-bought seedlings and transplants. Sow seeds indoors six to eight weeks before the last frost for planting out when all risk of frost has passed. As fully hardy shrubs, they can be planted at any time of the year except when the ground is frozen.
To help them establish quickly and to reduce the risk of frost damage to roots, set out 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 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. They 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 others won’t thrive. The added bonus of its deer-resistant nature means they are seldom severely damaged. You can grow it almost anywhere.
Other species to choose from include creeping St. John’s Wort (Hypericum calycinum), which works 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 one foot in diameter and fill with lots of fresh organic compost to add nutrients and improve moisture retention. Set the herb into the space, ensuring the stem is at the same level as the ground surface as in the pot.
How to Grow
St. John’s wort is a low-maintenance, extremely adaptable herb to grow in your own garden. Once established, it requires very little aftercare. Keep a watchful eye to contain its spread.
Light
Sun 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, this herb tolerates both full sun and almost full shade.
Water
When you grow St John’s Wort in the garden, keep the soil moist until young seedlings 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 it prefers 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, the shrubs will flower and thrive.
Temperature
Health will begin to deteriorate when daily temperatures are consistently above 75°F (24°C). Similarly, too much shade can stunt growth. Grow St John’s wort in USDA zones 3-8 for full hardiness. In colder zones, give your roots plenty of protection to see if they will perennialize. Herbs will benefit from winter mulch, especially if grown in wet soil.
Fertilizing
A good organic mulch in fall and/or spring is enough to keep St John’s wort going throughout the growing season. Fertilize shrubs planted in poor soils to help them bloom in summer through fall.
Maintenance
It isn’t necessary to prune when you grow St John’s wort unless they become untidy and need re-shaping. The yellow flowers develop on old wood. Prune back any new growth in early to mid-spring. This will provide shape and stimulate growth while ensuring the 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 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 one foot. Seeds can also be sown in the fall for transplanting the following spring.
Take softwood cuttings from new, non-flower growth in July/August. Cut four inches 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.
It can also be propagated by division in spring or fall. Carefully dig around the shrub 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.
Common Problems
St John’s wort looks after itself, sometimes too well, which is when it can become a problem. On a positive note, they are rarely affected by pests or diseases.
Growing Problems
St John’s wort is a very hardy and extremely adaptable shrub. It, 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. If left to its own devices may render land non-viable for other crops. The rhizomes can be difficult to remove once they take hold, so it’s important to keep on top of 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 them becoming invasive. Simply remove new seedlings as they pop up and before they become established. Prune seed heads when flowers have finished.
Frequently Asked Questions
Is the plant St John’s wort poisonous?
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.
St John’s wort 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.
Is St John’s wort the same as basil?
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 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.
What happens if a dog eats St John’s wort?
Dogs may be prescribed 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 herb may become unwell and develop photosensitized skin irritations. Seek medical advice if you have any concerns.
Is St John’s wort evergreen?
Hypericum perforatum, is a deciduous shrub, losing its leaves in fall/winter. There are lots of ornamental cultivars that are evergreen, such as Hypericum frondosum ‘Sunburst’, which has attractive winter berries as well as evergreen foliage.
