"St. John's Wort" conjures up the image of a brown-cowled monk, bent over a worn wooden mortar and pestle in a darkened herb shed leaning by his cloister's physic garden. While St. John's Worts were highly valued in medieval England for use in a variety of folk medicines, they should not be restricted to the herb garden. The variety of forms that Hypericums (St. John's Worts) bring to today's gardens can offer delightful beauty throughout the landscape.
The genus Hypericum includes a large number of species originating from a broad spectrum of climates stretching from Europe, through the Meditteranean, China and other parts of Asia, and across the Atlantic to North America, including the southeast. A number of species, and their hybrids and cultivars, are lovely garden plants. They range in character from evergreen and deciduous medium-sized shrubs to ground-covers and herbaceous perennials, but they all have in common a display of bright, sunny yellow flowers reminiscent of incredibly generous buttercups which develop into warm brown, capsule type fruits in the fall.
One of the best Hypericums for the southeast is the native Hypericum frondosum, Golden St. John's Wort. This deciduous shrub is hardy throughout the southeastern U.S. and is covered with 1-2 inch diameter butter gold flowers in June and July. The flowers of Golden St. John's Wort are unique compared to its other Hypericum cousins because the flowers' numerous stamens are densely clustered and form a lovely little tufted cushion in the center of each flower. Golden St. John's Wort gives one of the best floral displays of the Hypericums but it also has other special traits. The foliage is an especially handsome blue-green that makes a beautiful contrast with the golden flowers and, as the shrub reaches its mature height of 3-4 feet, the bark will peel to reveal an attractive red-brown color. There is a cultivar of H. frondosum, 'Sunburst' which is somewhat more compact and lower growing than the species.
Named for Peter Kalm of Sweden, Kalm's St. John's Wort, Hypericum kalmianum, is a 2-3 foot high, loose and open shrub with lemon yellow flowers in early July. It is hardy as far north as Michigan and Canada and may be evergreen in protected areas of the southeast. Kalm's St. John's Wort has somewhat fragrant flowers and the leaves are whitish on the undersides.
Hypericum patulum, Golden Cup St. John's Wort, is another handsome shrub form of St. John's Wort. It is somewhat shorter than the others, reaching a maximum of 3 feet, and has the added quality of semi-evergreen to evergreen foliage in the southeast.
Other good shrub forms of Hypericum include the hybrids H. x moseranum (Moser's St. John's Wort) and H. x 'Hidcote'. 'Hidcote' is hardy throughout the southeast. It reaches about 3 feet in height and sports very dark green foliage. 'Hidcote's flowers are somewhat larger than those of Golden St. John's Wort but they do not have the latter's delightful central tuft and they are more orange-gold in color than the clear butter of Golden St. John's Wort's flowers. Moser's St. John's Wort is a hybrid bred in Moser's Nursery of Versailles in the late 1800's. It is a compact and rounded shrub reaching 2-3 feet in height with a spread of about 3 feet. The foliage is blue-green and the golden yellow flowers are quite large, 2-3 inches across, with interesting pinkish-purple heads on the stamens. It flowers late in the season, from July through fall and is not as hardy as the other Hypericums so should be treated as a herbaceous perennial and cut back to the ground each winter. There is a white and rose variegated cultivar of Moser's St. John's Wort called 'Tricolor' grown at the famous Wisley Gardens in England but while the variegation is interesting, the habit of the plant is somewhat sparse and rangy.
Aaronsbeard St. John's Wort, Hypericum calycinum, is a woody groundcover form that only grows 1-1.5 feet tall but spreads to 2 feet. The large 3 inch wide flowers are an exceptionally bright and clear yellow set against dark green foliage. This lovely groundcover deserves greater attention in the landscape. While it may suffer some winter die back in mountain areas, flowers are formed on new wood so the flower display should remain unharmed. One way to handle this plant is to cut it back to the ground in late winter each year to stimulate a new flush of growth. Since growth is rapid, recovery and display will be improved.
A relatively new Hypericum, Hypericum forrestii, is a 3 to 4 foot tall deciduous shrub with golden yellow flowers set against smaller, finer textured foliage than the other St. John's Wort. Hypericum forrestii can have handsome, wine red fall color which adds to the seasonal interest of this shrub. It has not been planted out in trial at The NCSU Arboretum (now the JC Raulston Arboretum) but has been distributed through the Arboretum's introduction program for testing and evaluation in the field.
Culture of Hypericum varies a bit depending on the species or cultivar you are growing. All St. John's Worts prefer dry soils in full sun to partial shade but many will perform well in the clay soils of the southeast if placed in full sun. (MORE)
Best choices for long term performance in the humid south include H. frondosum, H. calycinum, and H forrestii. Many of the other St. John's Worts will be wonderful additions to the landscape for 2 years or so but may ultimately succumb to the hot, wet summers. St. John's Worts are easily propagated by softwood cuttings taken in the summer and rooted under mist in a light medium (like sand) or from seed which requires no special treatments.
The incredible array of St. John's Worts offers a delightful palette of sunburst golds for summer gardens. They make wonderful massed groupings along drives and walls as well as special accents in both mixed shrub borders and small scale landscapes. In the display beds of the Shade House, the Mixed Shrub Border and the West Arboretum, Hypericums bring a special kind of golden wealth to The NCSU Arboretum (now the JC Raulston Arboretum). Come out to the Arboretum to see how they can bring that richness to your own garden.