Mahonia — Oregon Grape
Mahonia is a genus of spiny-leafed, evergreen shrubs that includes approximately 70 species, the majority of which come from the temperate zones of East Asia, the remaining from North and South America. Some botanists maintain that the North American species be classified Mahonia, while others lump them into the Berberis genus despite the fact that the pinnate leaves and spineless branches of Mahonia differ markedly from the barberries in the Berberidaceae family, of which they are both members.
However they are classified, an estimated thirteen Mahonia species are California natives, prized for their handsome foliage, panicles of fragrant yellow flowers, large, leathery leaves with toothed margins, and miniature grape-like berries. Care must be taken when selecting plants for the home garden since some attain large, awkward size in maturity. A few are quite shrubby, while others are branched single-stemmed and form expanding colonies; and still others are groundcovers. The California natives are completely drought-tolerant once established; Asian species require moderate water.
Mahonia aquifolium: Oregon grape is one of the best known of the native mahonias, ascending as single stems or an erect shrub 3-7 ft. tall and spreading by rhizomes to form dense clumps. Its foliage, which is dark green and spiny, often begins as copper-colored in spring and may darken to purple or maroon, depending upon exposure to sun and/or cooler temperatures. M. aquifolium ‘Compacta’ grows 1-2 ft. tall and spreads up to 5 ft. wide or more with age. It is used as an attractive ground cover or low foundation planting. On both forms, yellow flowers provide nectar for hummingbirds; blue berries are a treat for robins, finches, and towhees; and they also make a delicious jelly.
Mahonia repens: Creeping barberry is considered one of the prettiest mahonias when its blue-green leaves turn metallic bronze or soft rose in winter. This low 1-3 ft. shrub is highly valuable as a cover for rocky terrain or slopes as it creeps by underground stems. Short, dense clusters of yellow flowers precede globular blue berries that attract birds. No supplemental water is required in shaded situations once plants are established. In full shade, this mahonia does not bloom.
Mahonia nervosa: Longleaf mahonia grows in colonies of stiff, single stems that bear 1½ -2 ft. long, leathery leaves with 20 or more dark green, red-veined leaflets that deepen to burgundy hues in winter. Fragrant clusters of yellow flowers and frosted dark purple berries complete the form and texture of this lovely woodland ground cover that somewhat resembles a leathery fern.
Mahonia nevinii: Nevin’s mahonia develops into a 6-12 ft. tall, 8 ft. wide shrub with rigid arching stems covered with pointed leaflets that open metallic grey and mature to soft blue-green. Yellow-gold flowers bloom profusely in spring, followed by an abundance of red-orange berries. This native mahonia has adapted well to Bay Area gardens. In the wild, it is fairly rare and is listed as an endangered species.
Mahonia pinnata: Native to coastal bluffs and scrubby inland woodlands along the Pacific Coast to Oregon, this species is valued for its crinkled, wavy, holly-like foliage that emerges with copper and reddish tints. Young shrubs are fairly compact, 4-5 ft. tall, and then begin to spread via underground runners, sending up more thick stems to form a colony. ‘Golden Abundance’ is even taller and wider and produces an abundant crop of large golden flowers followed by bluish-purple berries. ‘Ken Hartman’ and ‘Skylark’ are superior selections for their more compact growth to about 8 ft.
Several species lend themselves to sites where drama or an architectural statement is the foremost feature. Examples are M. bealei and M. lomariifolia , both of which have very long arching, prickly leaves with many leaflets on tall plants that often reach 10 ft. high and wide.