Family: Rhamnaceae
Common Name: Buckthorn

This is a genus of some 150 species of mainly deciduous, small trees and shrubs, mostly found in northern hemisphere temperate zones, although a few species are natives of Brazil and South Africa. Grown for their foliage and fruit, rather than their insignificant, green flowers, some species are also grown for their commercial value, as a source of dye, or used medicinally. In the US, they are grown in shrub borders or in woodland gardens. Some, such as R. fransuula and the spiny R. cathartica, both deciduous, make excellent hedges.

Species

R. alaternus, Italian buckthorn, zone 7, from the Mediterranean, is a large, evergreen, multi-stemmed shrub, 4-6 m (13-20 ft) high. It has small, dark, glossy, green leaves and blue-black fruits. It makes an excellent hedge or screening plant. Cultivar 'Argenteovariegata' has narrow leaves, marbled with gray, and edged with creamy white.

R. californica, coffee berry, zone 7, is an evergreen shrub, to 2 m (6 ft). The red fruit turns black on ripening. This species adapts to a wide range of growing conditions.

R. cathartica, zone 3, from Europe and parts of Asia, is a deciduous species with spines at the ends of the branches, and black fruit.

R. purshiana, cascara sagrada, zone 7, is a tall, deciduous shrub, to 6 m (20 ft), native to the north-western United States, where it grows as an understorey plant in tall forests. The bark is the source of cascara sagrada, a medical drug. The common name is from the Spanish word for 'sacred bark'. Early Spanish missionary priests came to learn its uses from the American native tribes in California. It has been used since the end of the 19th century as a laxative.

Cultivation

Rhamnus will grow in any well-drained yet moisture-retentive garden soil, from poor to reasonably fertile. They can be grown in full sun or in a position with partial shade. Very little pruning is required, but if they are being grown as a hedge, then trim annually, in late winter or early spring. Propagate from semi-ripe cuttings in summer, or by layering in spring.

Climate

There are species suited to various climatic zones.