Contact: Jil Swearingen, National Park Service | Jil_Swearingen@nps.gov
ANNAPOLIS, MD (December 1, 2006) – As its name implies, Japanese barberry (Berberis thunbergii) is native to Japan. It was introduced to the U.S. and New England as an ornamental plant in 1875 in the form of seeds sent from Russia to the Arnold Arboretum in Boston, Massachusetts. In 1896, Japanese barberry shrubs grown from these seeds were planted at the New York Botanic Garden. Many cultivars of Japanese barberry have been developed, all of which are considered to have invasive potential unless proven otherwise. There are two native species – American or Allegheny barberry (B. canadensis) which occurs in the East and Midwest and is endangered or extirpated in many states, and Colorado barberry (B. fendleri), a native to several western states. Because Japanese barberry fruit is highly visible in the woods during this season, MISC has chosen it as the December Invader of the Month.
Japanese barberry is a deciduous, spiny shrub that grows to about 8 feet. Its branches are brown, deeply grooved, somewhat zig-zag, and bear a single very sharp spine at each node, where the leaves meet the stems. The leaves are small (½ to 1 ½ inches long), oval to spatula-shaped and can be green, bluish-green, or dark reddish purple. Flowering occurs from mid-April to May in the northeastern U.S. Pale yellow flowers about ¼” across hang in clusters of 2-4 flowers each along the length of the stem. The fruits are 1/3“ long bright red “pips” (juiceless fruits) borne on narrow stalks. They mature during late summer and fall and persist through the winter.
Japanese barberry poses a threat to our native flora and fauna because it can form dense stands in wild areas including mature forests, open woodlands, wetlands, pastures, and meadows. Once established, barberry displaces native plants and reduces wildlife habitat and forage. It is shade tolerant, drought resistant, and adaptable to a variety of open and wooded habitats, wetlands and disturbed areas. It grows well in full sun to part shade but will flower and fruit even in dense shade. Changes in pH, nitrogen levels, and biological activity have been documented in soils infested by Japanese barberry. White-tailed deer appear to avoid it and prefer to feed on native plants, giving Japanese barberry a competitive advantage.
Japanese barberry spreads vegetatively and by seed. It produces large numbers of seeds with germination rates estimated to be as high as 90%. Turkey, quail, rabbits and other wildlife eat the fruits of Japanese barberry and disperse the plant to new locations by passing the seed. Vegetative spread is through root creeping, resprouting of root fragments, and rooting of branch tips that touch soil.
Photos: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
Effective control strategies for Japanese barberry are available for homeowners, professional landscapers, and managers of parks and preserves. Small plants can be pulled by hand when the soil is damp and loose, using thick gloves to avoid injury from the spines. The root system is shallow, making it easy to pull plants from the ground. Young plants can be dug up individually using a hoe or shovel. It is important to get the entire root system because Japanese barberry can resprout from root fragments. Repeated severe cutting or mowing will eventually kill the plants. Clipping, bagging and disposing of fruits will prevent dispersal from gardens into natural areas. For large infestations, herbicides containing glyphosate or triclopyr can be applied in late summer either to the foliage or as basal bark or cut stump applications, to further reduce potential impacts to native plants.
Choose attractive native shrubs for ornamental plantings as substitutes for Japanese barberry. Some examples include bayberry (Myrica pensylvanica), inkberry (Ilex glabra), winterberry (Ilex verticillata), arrow-wood (Viburnum dentatum), mountain laurel (Kalmia latifolia), ninebark (Physocarpus opulifolius) and hearts-a-bustin' (Euonymus americana). Check with the Maryland Native Plant Society, www.mdfloraorg for additional suggestions appropriate to our area.
For more information about other Invasive Species of Concern, visit the Maryland Invasive Species Council.