Rhamnus — Buckthorn and Coffeeberry
The genus Rhamnus includes about 125 species, but only two are grown with frequency in Sonoma County gardens: Rhamnus alaternus, Italian buckthorn, and Rhamnus californica, coffeeberry. Although these two species are fully evergreen, require little water once established, and grow in full sun but are tolerant of shade, they have completely different looks and growth habits.
Both can be used as a screen or wide hedge or in a habitat shrub border. Planted individually where there is ample space all around, they make a striking specimen. As a bonus, they are relatively free of pest and disease problems and are unattractive to deer. Both have flowers insignificant to gardeners but are highly favored by various pollinators; some varieties have showy berries in autumn.
These two Rhamnus species are amenable to pruning for controlling size and structure and can be elegantly shaped or left in their natural forms. When given plenty of space, they provide a backdrop for flowers and perennials as well as adding year-round interest to gardens. They remain green and lush through dry summers and cool, wet winters.
Italian buckthorn, Rhamnus alaternus, bears glossy, small, deep green pointed leaves. It is slow to get started—a five-gallon is usually the most satisfying size to plant—and takes a few years to fill out and develop girth. Where space allows, a row makes a privacy screen or windbreak. Its mature size is approximately 15 ft. tall and nearly as wide, not a small shrub. It’s important to keep these numbers in mind at planting time. Once pruning begins to control size, it becomes a never ending process to rein in annual growth.
Rhamnus alaternus ‘Variegata’ foliage has cream margins and deep green centers, beautiful markings sought after for informal floral arrangements. The structure and shape of the plant is the same as its green cousin but the leaf variegation results in an overall very light-colored shrub, a somewhat rare element in landscape shrubs. It is especially striking when planted against a darker background.
Coffeeberry, Rhamnus californica, is very different from Rhamnus alaternus although its cultural requirements are essentially the same. As the name suggests, this species is native to California and is found primarily in coastal regions as far north as southern Oregon. The leaves are much darker, larger—nearly 3 in. long—rounder and somewhat leathery with pale undersides. Berries decorate plants for several months as they ripen from pale green to orange-red to burgundy before turning black and eaten by birds and small animals.
Species plants found in the wild grow larger and lankier than most of the named cultivars, some reaching over 12 ft tall. ‘Mound San Bruno’ grows to about a 5 ft. high and wide and features narrower light green leaves and a dense form. It is considered to be the most adaptable coffeeberry for gardens.
‘Eve Case’ is sought after for its attractive large, showy berries and size—5-10 ft., key for including in a habitat shrub border. Leaves are a bit larger, darker and coarser than ‘Mound San Bruno’, but equally attractive. It is not quite as amenable to shaping, however, as is ‘Mound San Bruno’ and is best planted only in spots that are able to accommodate the mature size. In contrast, ‘Seaview’ rambles as a groundcover under 2 ft., spreading 6-8ft. wide.
Another variety with distinctive berries, ‘Leatherleaf’ is smaller than ‘Eve Case’ and a better choice for smaller gardens. It tops out around 5-6 ft. and has darker foliage with leaves that may reach 4-6 in. long.