Common St. John’s wort (*Hypericum perforatum*) is a plant species that is native to Europe and Central Asia. Common St. John’s wort is considered poisonous to livestock and can cause problems for humans if consumed. This dense, fast-growing plant has been introduced to North America and Australia, where it is often viewed as an invasive species.
I. Appearance and CharacteristicsÂ
Hypericum perforatum, commonly known as St John’s wort, is a flowering plant in the family Hypericaceae. It is a perennial plant that grows up to one meter tall, with many yellow flowers that have clearly visible black glands around their edges, long stamens (male reproductive organs), and three pistils (female reproductive organs). Probably a hybrid between the closely related H. attenuatum and H. maculatum that originated in Siberia, the species is now found worldwide. It is native to temperate regions across Eurasia and North Africa, and has been introduced to East Asia, Australia, New Zealand, and parts of North and South America. In many areas where it is not native, H. perforatum is considered a noxious weed. It densely covers open areas to the exclusion of native plants, and is poor grazing material. As such, methods for biocontrol have been introduced in an attempt to slow or reverse the spread of the species.
Hypericum perforatum is an herbaceous perennial plant with hairless (glabrous) stems and leaves. The root of each plant is slender and woody with many small, fibrous small side roots and also extensive, creeping rhizomes. The central root grows to a depth of 0.6–1.5 meters into the soil depending on conditions. The crown of the root is woody.
Its stems are erect and branched in the upper section, and usually range from 0.3 meters to 1 meter in height. The stems are woody near their base and look like they have segmented joints from the scars left behind after the leaves fall off. The stems of H. perforatum are rusty-yellow to rosy in color with two distinct edges and usually have bark that sheds near the base. The stems persist through the winter and sprout new growth with flower buds in the following year; first year growth does not produce flowers.
It has leaves that attach on opposite sides of the stems without a stalk (sessile). The leaves vary in shape from being very narrow and almost grass-like (linear), to a rounded oval slightly wider at the base with a rounded tip or not much of a tip (elliptic), or even narrow with the widest portion towards the end of the leaf like a reversed lance point, but still long and narrow (oblanceolate).
The principal leaves range in length from 0.8 to 3.5 centimeters and 0.31–1.6 centimeters in width. Leaves borne on the branches subtend the shortened branchlets. The leaves are yellow-green in color, with scattered translucent dots of glandular tissue. The dots are clearly visible when held up to the light, giving the leaves a perforated appearance. The edges (margins) of the leaves usually have scattered black dots, often called dark glands, though sometimes they will appear away from the edges. The odor of the plant is faint, but aromatic, resembling that of resins like balsam. The taste of the plant is bitter and acrid.
- Flowering characteristics
The flowers are conspicuous and showy, measuring about 1.5–2.5 cm across, and are bright yellow with black dots along the edges of the petals. Each of the flowers normally has five large petals and five smaller leaf-like sepals below them. The sepals are about 4–5 mm in length, green in color, are shaped like the head of a spear (lanceolate shape) with a pointed tip, and the same clear and black glands as the leaves. The petals are significantly longer, 8–12 mm in length, and have an oblong shape. They completely hide the sepals from the front side of the flower. The many bright yellow stamens are united at the base into three bundles. The stalk portion of the stamens, the filaments, vary in length and stick out in every direction from the center of the flower. The pollen grains are pale brown to orange in color.
The flowers are arranged along one side of each flowering stem with two flowers at each node (a helicoid cyme) at the ends of the upper branches, between late spring and early to mid-summer. Each flowering stem bears many flowers, between 25 and 100, and also is quite leafy.
The fruit of Hypericum perforatum is a capsule 7–8 mm in length containing the seeds in three valved chambers. Seeds that are separated from the capsules have a much higher germination rate due to an inhibiting factor in the capsule itself. The black and lustrous seeds are rough, netted with coarse grooves. Each seed is about 1 millimeter in size. Each plant may produce an average of 15,000 to 34,000 seeds.
- Similar species
Hypericum maculatum is visually similar to Hypericum perforatum; however, its stems have four ridges instead of two and are also hollow. In addition, its leaves have fewer translucent glands and more dark glands. H. maculatum is native to the Old World but has also been introduced to North America.
In North America several native species may be confused with Hypericum perforatum. Hypericum anagalloides is a low-growing creeping plant with rounder leaves and fewer stamens. Hypericum boreale is a smaller plant with more delicate flowers. Hypericum canadense has smaller flowers with sepals that show between the petals. Hypericum concinnum has flowers with petals that bend backward at the tip and also has much narrower, gray-green leaves. Growing in riparian areas along rivers, Hypericum ellipticum has wider leaves with a more elliptic shape. Hypericum scouleri has leaves that are broader at the base and also thicker. All except for H. concinnum grow in environments that are generally more moist than where H. perforatum is found.
- Toxicity
Hypericum perforatum is toxic to numerous domestic animals such as cows, sheep, and horses. When these animals come into contact with the plant, usually through grazing, they develop serious symptoms. The first signs are reddening of the skin accompanied by swelling, which is followed by necrosis and sloughing of the skin. Non-pigmented, white skin is most affected by the poisoning, such as the nose and ears of certain breeds of sheep. Young animals are more susceptible to H. perforatum poisoning, and the plant is most toxic in spring (when it is the most palatable to herbivores) and retains its toxic effects when dried in hay.
Additionally, affected animals will become highly photosensitive, and exposure to sunlight can exacerbate their symptoms. As such, they should be moved to a dark area; administering antihistamines or anti-inflammatory medicines may also help alleviate the symptoms.
II. How to Grow and Care
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.
Planting Instructions
Plant common St. John’s wort in the early spring or early fall. Choose a cool, shaded place, such as within tree shade. Remember to clear the soil first and remove weeds. Dig a planting pit slightly shorter than the diameter of the root ball and 3 times wider. If you’re planting more than one sapling, avoid planting them too close, or low light and poor ventilation may result in powdery mildew. Pile some soil around the root collar (the juncture of trunk and roots) to form a gentle slope, and this helps disperse water. After planting, press the soil firmly and water thoroughly. Note the distance between each.
Some plants in the Hypericum genus have subterraneous rhizomes that tend to expand in all directions. To prevent excessive expansion, it’s a good idea to fence the planting spots or set brick perimeters around them to control their growth.
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.
Pests and 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, 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.
- Common Pests
There are no persistent garden pests that affect the growth of this plant.
- Common Disease
In addition to having few pests, Hypericum perforatum is relatively disease resistant also.
III. Uses and BenefitsÂ
- Ornamental uses
Common St. John’s wort is an attractive garden ornamental with ornate, star-shaped flowers. It is often viewed as a weedy plant, but is grown in prairie and meadow landscapes where it is useful in attracting pollinators. Common St. John’s wort is also grown in herb gardens, wildlife gardens, as borders and woodland margins.
- Traditional medicine uses
Dried Hypericum perforatum for use as an herbal drug called “herba hyperici”
Common St John’s wort has been used in herbalism for centuries. It was thought to have medical properties in classical antiquity and was a standard component of ancient concoctions called theriacs, from the Mithridate of Aulus Cornelius Celsus’ De Medicina (c. 30 CE) to the Venice treacle of d’Amsterdammer Apotheek in 1686.
One folk use included the oily extract known as St John’s oil, a red, oily liquid extracted from H. perforatum that may have been a treatment for wounds by the Knights Hospitaller, the Order of St John. Another part of the plant that is used is the dried flower structure, which is turned into a product known as “herba hyperici” by crushing.
