Most members of the Hypericum genus are weeds and are often classified as being an invasive species. Before growing members of this genus in your garden you should carefully consider how the selected species will thrive in your local area; only grow if it is not considered a risk.
Plants of this genus are poisonous to cattle and their invasiveness can cause major issues; especially in humid areas.
As a fairly large genus (490 species) it has numerous different growing habits, commonly as annuals, perennials and shrubs, but it can even grow as single stemmed tree, with the species Hypericum bequaertii being able to reach a height of 33 feet (10 m).
Many plants belonging to the Hypericum genus are hardy perennials that range in height from 6 inches to 6 feet (15 to 180 cm), and they come into bloom in the summer or autumn. They are shrubby in nature, carrying wonderful yellow, saucer shaped flowers.
Shrubs and perennials differ greatly in that the latter produces root from horizontal nodes that touch the ground. Annuals have taproots.
Leaves are opposite and are marked by distinctive pale or dark glandular dots. These contain chemicals known as naphthodianthrone and hypericin. When a leaf is crushed they produce a red secretion from these secretions. Flowers are generally yellow with four or five sepals and asymmetric petals. The colour of the flower varies from shades of lemon to deep yellow through to orangey yellow; the petals may are also often tinted or lined with a deep crimson red.
Hypericum perforatum is better known as Common St John’s Wort and has long been used in traditional medicines to help treat depression. Even today it is often used as a replacement for expensive and over powerful prescription medications.
It has been noted that St John’s wort may interact in a negative way with prescription drugs, so if you intend to take it be sure to have a chat with your doctor beforehand.
Though most members of this genus are noxious weeds some species have had cultivars developed for use as an ornamental plant in gardens. Well Known Species include:
Hypericum androsaemum (Tutsan), this deciduous bushy shrub reaches about 3 feet (90 cm) in height and spread. It grows well in USA zones 5 to 9; UK Hardiness H5. It blooms in the summer with showy yellow flowers and is often used as an hedging plant in shady areas.
Hypericum calycinum (Rose of Sharon). Hardy in the US in Zones 5 to 10: UK H6. Small shrub to about 18 inches (45 cm) with a slightly larger spread to 24 inches (60 cm). Often used as groundcover and in areas with erosion. Bright yellow flowers in summer. Drought tolerant.
Hypericum Hidcote (St. John's wort ‘Hidcort’). Shrub of two to four feet (60 cm to 1.2 m). Golden saucer shaped flowers in the summer; three inch (7.5 cm diameter. USA zones 5 to 9; UK Hardiness H5.
Depending on species type, they can be used in different parts of the garden: small species are great for rock gardens, whereas larger ones are good to use in garden borders. Names for Hypericum plant genus members include St John's Wort (St John’s wort), Aaron's Beard, and Rose of Sharon.
Common Names: St John’s Wort (Hypericum perforatum), Tutsan, Aaron’s Beard, Rose of Sharon.
Life Cycle: Hardy perennial. Hardy Annual.
Height: 3 to 72 inches (8 to 180 cm); shrubs and small trees may reach heights of 470 inches (1200 cm).
Native: Worldwide apart from Antarctica.
Growing Region: Zones 5 to 9. UK Hardiness: H5 to H6
Flowers: Species dependent: Summer and/or autumn.
Flower Details: Yellow. Saucer shaped. Fluffy Stamens. Usually five petals.
Foliage: Herbaceous. Evergreen. Opposite. Ovate.
Sow Outside: Seeds: cover. Start of spring or the beginning of autumn. Spacing 6 to 36 inches (15 to 90 cm) dependent upon species size.
Sow Inside: Germination time: three weeks to three months. Temperature: 50 to 55°F (10 to 13°C). Two months in advance. Transplant three weeks in advance of the expected last frost or at the start of autumn.
Requirements and care: Full sunlight or partial shade. Can grow in many soils but good drainage and a pH of 5.5 to 7.0 for best results. Prune at the beginning of spring. Propagate: by dividing in the autumn following flowering, or by taking cuttings in the spring and summer.
Miscellaneous: An invasive weed in many areas. Can cause photosensitivity. Used in traditional medicine as an anti-depressant and as an antibiotic. St John’s wort is thought have abortive effects and should not be taken by pregnant women, nor by people seeking suntans. As it interacts badly with many medicines, especially those involved in the treatment of cancer and HIV, Hypericum use should only be used under the advice of a doctor.
You can grow St John's Wort and other Hypericum outdoors from seeds. These should be sown out in either early on in spring or towards the beginning of autumn. Once sown lightly cover the St John's Wort seeds. Hypericum plants can grow in either a sunny area of the garden, or one that receives part shade. They prefer a well drained slightly acidic soil of pH 5.5 to 7, but the type is not overly important.
If you first plan to grow Hypericum indoors then the growing process should start about two to two and a half months before they are due to be put out, either before th last frost of spring or at the beginning of autumn. Hypericum will take from three weeks to three months to germinate at a temperature of about 10 to 12 degrees Celsius.
Hypericum basically look after themselves once established in the garden. They require a good prune at the start of spring however. If you require more plants then cuttings can be took in the spring or summer; or you may prefer to divide the plants; this can be done in the autumn once flowering has finished.
I hope that you enjoyed this guide on how to grow Hypericum plants. Updated September 2020.