St. John’s wort: growing, pruning & uses

St. John’s wort (Hypericum) are popular perennials that can be found in many home gardens. Here is our helpful introduction to this ancient medicinal plant as well as tips on cultivation, care and use.

St. John’s wort is a widely known garden and medicinal plant. Read on to learn all about the properties of this plant as well as how to successfully cultivate St. John’s wort.

St. John’s wort: origin and properties

The genus St. John’s wort (Hypericum) consists of 500 – 700 species that are distributed worldwide. They are part of the St. John’s wort family (Hypericaceae). Several species are native to our latitudes, such as Hypericum perforatum, which is simply called St. John’s wort. The plant has been associated with Christianity for many centuries because its name was derived from John the Baptist, whose blood is said to have flowed into the flowers of St. John’s wort after his beheading. If you rub the yellow petals between your fingers, the sap that comes out is tinged red.

St. John’s wort is a perennial herb that, depending on the species, is evergreen or dies above ground in autumn and grows again in spring. The plant grows to an average height of 60 – 80 cm but there are also low-growing, ground-covering species and much taller ones up to 150 cm. St. John’s wort usually forms several branched stems that can be round, angular or winged and are green to brown in colour. The oval to lanceolate blue-green to green leaves of St. John’s wort often have many transparent or dark spots – these are oil glands. The five golden-yellow petals can also appear perforated; this is particularly striking in the case of spotted St. John’s wort (Hypericum maculatum).

Bees and other pollinating insects like St. John’s wort flowers as they provide food in midsummer and into autumn. The flowers also have numerous stamens that protrude from the centre as thin filaments, bestowing pollinators with their pollen. The flowering period of St. John’s wort usually begins around St. John’s Day in June and can last until October. After pollination, either green-brown capsule fruits or brightly coloured fleshy berries form.

Please note: a plant similar to St. John’s wort is the poisonous ragwort (Senecio jacobaea). If you look closely at the small ragwort flowers, you will notice they have a different structure to St. John’s wort flowers and lack protruding stamens. Ragwort flowers look a bit like daisies and the plant has an alternate leaf arrangement with pinnate leaves.

How to grow St. John’s wort

Depending on the species, St. John’s wort has different requirements for its planting site but generally, it is undemanding and tolerates many locations. A good choice for St. John’s wort is a sunny to semi-shady spot with humus-rich, well-drained soil. Some species prefer acidic soil, while others like calcareous soil and water levels vary from moist to dry.

You can either buy St. John’s wort plants in perennial nurseries or sow and grow your own. They are light and cold germinators, meaning that the seeds need a long cold period at the beginning. Afterwards, cover them with little to no soil so they receive plenty of light to germinate. You can pre-treat the seeds in the fridge for 6 weeks and then sow them. Sow the elongated, red-brown seeds on low-nutrient growing soil, such as our Plantura Organic Herb & Seeding Compost. Press the seeds down lightly and only slightly cover them with soil. Place the seed tray in a bright but not sunny spot at around 20°C and keep the soil moist. The first St. John’s wort seedlings will appear after 2 to 3 weeks. Alternatively, sow the seeds outdoors in autumn and leave them out in the cold. St. John’s wort has a high germination rate, so some seeds will certainly emerge in the following spring. The seedlings can be pricked out or transplanted after a few weeks.

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The best time to plant hardy perennials is in late autumn between October and late November. Alternatively, they can be planted in early spring before the leaves emerge at the beginning of March. Young perennials that have not yet been able to form roots will need regular watering in summer. In the garden, St. John’s wort can be planted in groups or individually, and dwarf varieties can be planted as a ground cover. The planting distance for groups is about 40 cm, which is about 6 – 8 plants per square metre. For hypericum ground cover, use low-growing St. John’s wort species such as Aaron’s beard (Hypericum calycinum) and plant 12 – 15 per square metre. Larger growing varieties such as Golden Cup St. John’s wort (Hypericum x patulum or hypericum hidcote) need to be spaced 1.5 – 2 metres away from other plants. Here is how to plant St. John’s wort:

• Loosen the soil and work in some mature compost if necessary
• Dig a sufficiently large and deep planting hole
• Place St. John’s wort in the hole, fill with soil and press down lightly all around
• Give the plant plenty of water

St. John’s wort in a pot: St. John’s wort can be cultivated in a pot as long as the pot volume is at least 5 litres. It is important to have good water drainage and a 5 cm drainage layer of sand, gravel or expanded clay at the bottom of the pot. If kept outdoors in winter, provide the pot with insulation.

Summary: Planting St. John’s wort

• Sowing: indoors with cold treatment or outdoors in autumn
• Habitat: sun to partial shade
• Soil: humus-rich and well-drained; acidic or calcareous depending on species, moist to dry
• Time: October to November or beginning of March
• Planting distance: 40 cm (in groups), 1.5 – 2 m (individually), 12 – 15 plants/m2 (ground cover)

St. John’s wort plant care

St. John’s wort is a low-maintenance ornamental and medicinal plant. It will need watering most in the first year after planting and in hot, dry summers.

If you would like to make the most out of the benefits of this perennial herb, avoid over fertilising it – a high nitrogen supply reduces the content of beneficial substances. An annual application of compost or mainly organic slow-release fertiliser such as our Plantura All Purpose Plant Food in spring at budbreak is sufficient for St. John’s wort.

In addition to pruning at harvest time, St. John’s wort is also cut back in spring. With deciduous St. John’s wort, remove all dead parts of the plant before budding to give it space to grow. With evergreen St. John’s wort, remove frostbitten or old and injured shoots should be in spring.

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St. John’s wort propagation

St. John’s wort can be propagated by seeds and by cuttings. To collect St. John’s wort seeds yourself in autumn, gather the capsules or berries in October and leave them to dry at room temperature for a few weeks. Once the capsules are dry, the seeds will come out easily. St. John’s wort berries need to be broken open to release the seeds. The seeds can be stored in a dry, cool and dark place for several years without losing their germination capabilities.

To propagate from cuttings, take 10 cm long cuttings from the young shoot tips before flowering in May. Defoliate these shoots down to the tip and placed in low-nutrient growing soil with added sand. Place the planted cuttings in a well-lit room at about 20 °C and keep the soil moist. The first roots will form after a few weeks. Hypericum cuttings can be planted out in autumn of the same year.

Tip: the rootstock of deciduous perennials can also be divided. To do this, simply cut off a piece of the rootstock with a spade in autumn and transplant it.

Is St. John’s wort hardy?

Yes, St. John’s wort is hardy in our latitudes. Waiting to cut back dead above-ground parts of the plant in spring will provide additional protection for the perennial. St. John’s wort in pots need some extra protection in winter – you can insulate potted St. John’s wort with jute bags, needle twigs or fleece.

Harvesting and using St. John’s wort

Only the Hypericum perforatum St. John’s wort is used for medicinal purposes. The above-ground parts of the plant are collected when St. John’s wort flowers from June onwards. It is best to harvest St. John’s wort in the early morning, which is when the amount of active beneficial ingredients such as hypericin is at its highest. Cut either the whole plant or just the flowers and individual leaves. After harvesting St. John’s wort, make sure to use it quickly to preserve the beneficial ingredients. You can prepare tinctures with it or dry the leaves and flowers for St. John’s wort tea. To make St. John’s wort oil, fill a bottle with St. John’s wort blossoms and high-quality vegetable oil and store it in a sunny and warm place for about six weeks. The red oil can be used for several months.

St. John’s wort uses

St. John’s wort preparations such as capsules, extracts and oil are used to treat depression, anxiety and nervousness. Used externally for skin care, St. John’s wort oil relieves muscle pain and skin irritations. The oil also promotes wound healing and has an anti-inflammatory effect. However, always speak to your doctor first before using St. John’s wort to avoid drug interactions. One of the side effects of St. John’s wort is increased sensitivity to light – light-skinned people therefore need to avoid sunbathing when taking St. John’s wort.

Is St. John’s wort poisonous?

St. John’s wort is classified as slightly toxic, as its consumption can make the skin sensitive to sunlight. Grazing animals with white coats such as horses, sheep and goats can suffer from Hart’s disease after excessive consumption of St. John’s wort in combination with exposure to the sun.