A Japanese barberry, Berberis thunbergii, is an ornamental plant in the barberry, or Berberidaceae, family. The plant has a sharp thorn under each cluster of leaves, so it is ideally suited as a barrier plant. Also known as Thunberg’s barberry or red barberry, the shrub is frequently grown as a hedge or in parking lot islands. A number of different cultivars have been produced, including red chief, red pillar, and rose glow. In many places, this barberry has become an invasive weed and out-competes native vegetation.
This deciduous shrub grows 3 to 6 ft (0.9 to 1.8 m) tall and can spread to 7 feet (2.1 m) wide. The plant blooms in the spring, producing small yellow flowers that give rise to 1/3-inch (1 cm) elliptical or round red fruit, each containing one seed. The fruit stay on the plant and attract birds. The stems of this shrub are reddish, and the leaves can be green or purple and turn red in the fall. Part of the attraction of growing Japanese barberry is the fall and winter color provided by its red leaves, stems, and fruit.
This shrub grows under a wide range of conditions, in full sun or shade. It can tolerate a wide array of soil types and has moderate tolerance to drought. The plant has a low tolerance for salt, however. Japanese barberry can grow in warm climates, such as that of Florida, and northern climates, like those of Nova Scotia, Canada. It is not eaten by deer.
Japanese barberry was promoted as an alternative to common barberry, or Berberis vulgaris. The latter plant serves as a host for part of the life cycle of a devastating pathogen known as wheat stem rust. It has served as a reservoir to spread the deadly fungus to wheat crops.
There were huge eradication programs in the U.S. during the 20th century to rid the country of the common barberry, particularly in the northern states. The wheat rust cannot over-winter without the barberry, so eliminating the shrub kept the pathogen at bay. In the U.S., wheat stem rust does not live on Japanese barberry. Canadian researchers have found that some varieties of this barberry do harbor the fungus, and it is illegal to grow the shrub in Canada.
A large problem with Japanese barberry is that it has a tendency to spread into areas of local plants and establish itself as large thickets. It can crowd and shade out the native plants and change the pH and nitrogen levels of the soil, reducing the amount of habitat available for local wildlife. This is a particular problem in forests. Birds spread this shrub by eating the fruit and then dispersing the seeds. Also, branches that come in contact with the ground can root, creating new plants. Thus, this barberry can spread to form giant thickets.
Japanese barberry can be controlled manually by pulling the young plants. Also, it is sensitive to several herbicides. Being one of the first shrubs to produce leaves in the spring, it is easily spotted. Thus, the barberry can be specifically treated with herbicide, so there is only minimal damage to the surrounding native plants. In areas prone to wildfires, it is thought to be easy to control, since it appears to be killed by fire.
This shrub contains the alkaloid berberine. The nitrogen-containing compound has been used in traditional medicines. A number of claims are made for its therapeutic uses, but those remain unsubstantiated.