Exotic---also known as non-native or alien---plants are those that have been transported, deliberately or otherwise, to regions outside of their natural habitats. Their new homes are free of the insects and diseases the control the plants' spread, giving them an advantage over the local vegetation. They may become invasive, choking out other plants and depriving wildlife of critical food and shelter. Many of New Jersey's exotic plants and shrubs, says Herbert Ling of the state's Native Plant Society, are frequently used in home landscapes.
Japanese barberry (Berberis thunbergii) is one of 69 plants on the National Park Service Plant Conservation Alliance's (NPSPCA) Least Wanted list. A densely branched, spiny flowering shrub between 2 and 8 feet high, drought and shade-tolerant Japanese barberry came to the United States in 1875 promoted as a landscape ornamental. It now grows wild in open woods, wetlands, forests and pastures.
Classified as invasive in New Jersey and 19 other states, the shrub alkalizes soils, making them inhospitable to some native plants. Deer avoid feeding on Japanese barberry. Birds and small mammals, however, eat the shrub's berries and spread its seeds. Branches of the plant that touch the soil will root, producing new bushes. Manual removal of plants and all root fragments is the most effective way of controlling Japanese barberry.
Like Japanese barberry, common buckthorn (Rhamnus cathartica) came to the United States as an ornamental flowering shrub or tree. It's now considered an invasive exotic in New Jersey and 23 other states. Extremely hardy and shade-tolerant, buckthorn can grow up to 22 feet high and survive in a range of soils. It takes over oak woods, open fields and prairies. Common buckthorn produces berries that fall directly beneath them. The seedlings form dense thickets that choke out native plants, says the NPSPCA. Controlled burning is one effective way of eradicating buckthorn infestations. Others are applying herbicide to the plant's freshly cut trunk, and uprooting small seedlings manually or with a weed wrench.
Japanese Tree Lilac
One exotic shrub that has found a welcome in New Jersey---and across the United States---is the Japanese tree lilac (Syringia reticulata). The first of them arrived at the New Jersey Botanical Garden in 1928. Native to northern China, this shrub can grow to 30 feet high. From late spring to early summer, it bears profuse, upright clusters of fragrant, creamy white blooms against a background of dark green leaves. New branches have reddish bark that becomes gray over time.
This easy-to-grow shrub works as a single specimen or in groups. For best results, plant it in full sun and averagely moist, well-drained soil. Remove the spent flower spikes before they set seed. If necessary, prune the plants immediately after flowering.