Japanese Barberry: So Beautiful Yet So Harmful

To be placed in this less than desirable category, a plant must be "determined to be injurious to public health, crops, livestock, agricultural land or other property." This listing allows nurseries and propagators time to decrease inventory. In one year (Fall 2022), warning letters will be issued to anyone selling Japanese barberry. Finally, Stop Sale/Destruction orders will be issued in Fall 2023.

Japanese barberry, Berberis thunbergii, was introduced into the U.S. in the mid-1800s as an ornamental plant. The plant was and still is popular as its attributes are numerous, especially with decades of plant selection and breeding. While the foliage of the straight species is green, the cultivars have brought a rainbow of color to the landscape. The spectrum ranges from purple ('Crimson Pygmy') to yellow ('Aurea') to many color combinations ('Rose Glow' – new foliage is rose-pink, mottled with deeper red-purple blotches).

Figure 2. (Left) The availability of barberry foliage in various colors adds interest and variety to the landscape. 'Rose Glow' with red-purple blotches. (Right) The availability of barberry foliage in different colors adds interest and variety to the landscape. 'Crimson Pygmy with purple foliage. Photos: Michael Masiuk, Penn State

Figure 3. The availability of barberry foliage in various colors adds interest and variety to the landscape. A hedgerow of 'Aurea' with yellow leaves. Photo: Michael Masiuk, Penn State

Beyond the colorful foliage, it has several other seasonal interests. While the individual flowers are small, the numerous blooms in April and May add some beauty, especially plantings close to pedestrian areas. Bees, wasps, ants, flies, and beetles are all-important visitors. Fruits soon follow when adequately pollinated. Once mature, the berries turn bright red in fall and persist well into winter. The literature states that it is not a preferred food source for birds and will bypass until other foods are unavailable. At that point, numerous species (mockingbirds, blackbirds, cedar waxwings, etc.) will feast upon the berries in late winter.

Figure 4. Small yellow flowers hang under the leaves of Japanese barberry Photos: Tom Butzler, Penn State

Spines run up each stem serves several functions. It can be used as a barrier plant along paths or between yards to keep foot traffic contained. Throw in the dense, twiggy habit, and it is almost impenetrable. But those spines also serve as a detriment to deer browsing. It's a great addition to a landscape that is a busy thoroughfare for deer.

While some of our landscape plants are on the picky side of site conditions), barberry is highly adaptable to growing zones (USDA 4-8), range of soil characteristics, varying light levels, and rural and urbanized conditions. With its toughness and beauty, it is a landscaping favorite.

Figure 5. (Left) A dense thicket of Japanese barberry off the Pine Creek Rail Trail in Lycoming County. (Right) Spines on Japanese barberry stems make for an excellent living hedge and deer deterrent. Photos: Tom Butzler, Penn State

However, many of those attributes have allowed it to thrive in disturbed and naturalized areas. Its prolific berry production and allure to birds have followed with excellent seed dispersal. It can grow in a sunny location but feel just at home in the forest's understory. The same dense growth that makes it an excellent living fence prohibits native vegetation from growing underneath. Deer provide no control as they refuse to browse on Japanese barberry and concentrate on native vegetation of our forests.

But research is also showing that barberry is a problem to our natural ecosystems and our health. Researchers at the Connecticut Agricultural Experiment Station discovered that stands of barberry harbor many more times the number of Lyme disease-carrying black-legged ticks than those free of barberry.

The increased humidity under that dense barberry stands is less stressful for young ticks (they will dry out in the more open areas) and allows their population to flourish. In addition, dense, spiny growth is an excellent habitat for mice as they can easily avoid predators. Those two combinations create the perfect storm.

While deer are a vital host late in the Lyme disease life cycle, mice play a critical role in the early stages. Upon hatching, young ticks (nymphs) don't carry the bacteria that cause the disease. The hungry nymphs latch onto the mice, reservoirs for the disease-causing bacterium. After feeding and acquiring the bacteria, the nymphs drop off the mice. They are ready to feed on larger animals, such as humans. But now, they carry the bacteria that contribute to Lyme disease.

Figure 6. Small rodents, like mice, play an essential role in the spread of Lyme disease. Image: Penn State