BY TOVAH MARTIN / Roxbury, Connecticut, USDA Zone 5
ON THE WEB
Invasive Plant Atlas of New England
Want to know if a plant is becoming a problem in your area? Go online to the Web site of the Invasive Plant Atlas of New England (IPANE), a joint project with the University of Connecticut, the New England Wild Flower Society, and the U.S. Fish and Wildlife Service, operating under a grant from the USDA. Its goal is to provide up-to-date information about invasive plants in New England in order to educate the public and support early detection of potentially invasive plant species. For more information about IPANE, visit http://invasives.eeb.uconn.edu/ipane.
Beware the Barberry
Following a backbreaking binge spent ridding my woods of Japanese barberry, I occasionally cast a suspicious glance over at the purple-leaved cultivars of Berberis thunbergii planted wholesale in nearby shopping mall parking lots and wonder if they could be blamed for the population explosion on my side of the fence. According to a recent study, the answer is pointing toward the suspicious side—handsome though they might be, several ornamental cultivars of Japanese barberry seem to have the potential for contributing to the spread of the species.
Like many invasive nonnatives, Japanese barberry was originally welcomed into this country. According to John Silander, professor of ecology and evolutionary biology at UConn and active with the IPANE (Invasive Plant Atlas in New England) program, when the Japanese native Berberis thunbergii hit the nurseries around 1900, it was warmly embraced as a replacement for our native B. vulgaris, which was blamed for spreading a cereal rust that damaged agricultural crops. Easily propagated and tolerant of a range of conditions, it seemed the answer to any nurseryman’s or landscaper’s prayers. But there was a glitch: Japanese barberry sets a super-abundance of viable seeds that are stripped by birds and broadcast throughout the landscape. By 1910, Japanese barberry had already begun escaping from cultivation; it wasn’t until 50 years later, though, that a concerted eradication effort was initiated. By that time, the damage had been done.
In the meantime, Japanese barberry was flexing its substantial muscle on the commercial front. Forms with colorful foliage and dwarf growth habits burst onto the scene and were scarfed up by gardeners eager to plant something both good looking and easy to maintain. According to Mark Brand, professor of ornamental horticulture and co-head of the plant biotechnology facility at UConn, in Connecticut alone, Japanese barberry cultivars currently account for at least $5 million in annual sales, placing it among the top ten most popular landscape shrubs. So these “horticulturally useful but potentially problematic plants,” as Dr. Brand calls them, have a substantial following in the trade.
Everyone would have liked to hear that the cultivars did not do dirty deeds similar to the nonnative species. Unfortunately, according to the study now in its third year at UConn, some fancy-leaved and dwarf cultivars also set viable seeds, which are dispersed hither and yon. So far, Berberis thunbergii f. atropurpurea (pictured) and the cultivar ‘Rose Glow‘ are clocking in as the most prolific seed setters, forming fruit with a gusto that equals the species. The dwarf variety ‘Crimson Pygmy’ doesn’t bear as prolifically. And the yellow form, ‘Aurea’, also produces a reduced quantity of offspring. There were a few mitigating factors, however. In UConn’s trials, seed production might have been stifled by the fact that the barberries were being grown in shaded, unmanaged areas, compared to the sunny, cultivated situations that cultivars generally enjoy.
So, is there any hope for barberry? Dr. Brand and the UConn team are working to create reliably sterile cultivars that won’t be fruitful and multiply. But that’s in the distant future. For now, it’s wise to beware of barberry in all its guises. H
Caroline Donnelly Richardson, manager of horticultural information at the Arnold Arboretum, recommends cotoneaster as a low-growing, low-maintenance alternative to barberry. Although it isn’t a dead ringer, many of the smaller mounding varieties have compact dimensions similar to Berberis thunbergii. Cotoneaster dammeri and its cultivar, ‘Coral Beauty’ (pictured), have persistent foliage, while the deciduous varieties display excellent autumn color. Although many cotoneasters can tolerate partial shade, they prefer full sun.
Tim Wood, of Spring Meadow Nursery in Michigan, suggests Weigela ‘Midnight Wine’–with its dwarf stature, dark burgundy foliage, and tolerance of partial shade—as another good alternative. “Plus, it has flowers and no thorns,” he adds. He also recommends Buxus ‘Green Velvet’. “It’s the hardiest, best-looking boxwood,” Tim offers, “and it’s so shade tolerant that it will survive under a dense tree canopy. Not many shrubs will do that.” Sources, page 77.