BY C. COLSTON BURRELL/Free Union, Virginia, Zone 7
The allure of exotic plants is inescapable. In spite of a rich and beautiful native flora, we are invariably drawn to plants from distant shores. As a result, our gardens rely heavily on plants native outside our region. Most of the plants we introduce into our gardens are not problematic, but from time to time a plant adapts too well to its new home and spreads beyond the garden. These invasive exotic species compete with native plants for a place in the sun, altering the structure and function of the ecosystems they invade. The American Lands Alliance has identified nearly 500 invasive species across North America, with 57 percent still sold for ornament, erosion control, or forage. In Virginia 115 species are documented as invasive.
When a plant escapes cultivation and settles into a native ecosystem, problems arise. Simple physics dictates that two plants cannot occupy the same spot, so when an exotic gets in, it displaces a native. Once a plant is entrenched it begins to proliferate, growing faster, taller, or wider, and shading out smaller plants. Many stay green later into the season or leaf out before other species, which gives them an advantage over natives. Alien plants can change the vertical and horizontal structure of ecosystems, alter hydrology, and corrupt nutrient cycles, all to devastating effect on native plants and animals.
Not every invasive species acts the same in all parts of the country, or in all ecosystems within a region, however. The hedging shrub buckthorn (Rhamnus cathartica) is a major problem on glacial and calcareous soils, but not on acidic soil. It is not established in most of Virginia, but is rampant in the Shenandoah Valley on limestone bedrock. Purple loosestrife (pictured), on the other hand, has become the poster child for invasive exotics in many different regions of the United States. It may be too late to control this and other firmly entrenched species, but you can help by removing them from your property. Unbelievably, some known invasives in the Middle Atlantic region—Norway maple (Acer platanoides), Asian bittersweet (Celastrus orbiculatus), elaeagnus, euonymus, ivy (Hedera spp.), honeysuckle (Lonicera spp.), privet (Ligustrum spp.), nandina, and Rosa multiflora—are still being sold, despite their documented ability to degrade ecosystems.
In addition to the thugs we know, the next wave of emerging invasive plants also needs to be scrutinized and eliminated from our gardens. Some popular ornamental plants that are becoming all too familiar in Virginia's meadows, hedgerows, and woodlots include lesser celandine (Ranunculus ficaria), Japanese silver grass (Miscanthus sinensis), sweet autumn clematis (Clematis terniflora), golden rain tree (Koelreuteria paniculata), and kousa dogwood (Cornus kousa).
The way to stop the spread of an invasive plant is not to buy it. If you want more information on invasive alien plants, contact the Virginia Native Plant Society (www.vnps.org/invasive.html). H
American elderberry (Sambucus canadensis)
Elderberry is as useful as it is beautiful. Creamy flowers borne in broad flat clusters impart a unique flavor when added to savory corn fritters or steeped in syrup for use over fresh fruit. The purple berries make luscious jam, but be sure to share them with the mockingbirds and others who also relish them. Arching stems clothed in pairs of elegant, pinnately divided leaves form a broad-crowned shrub to 12 feet tall and wide. ‘Aurea’ is stunning, with glowing yellow leaves. Hardy in USDA Zones 3 to 8.
To do in the garden
- Now is a good time to survey your property for invasive species. Mark plants with flagging tape or a blaze of spray paint. Eradication is often a long process, so start now.
- Pull or dig out invasive herbaceous species and dispose of the roots and seeds.
- Small shrubs such as honeysuckle and burning bush are easy to pull or dig in late summer.
- Cut down larger invasive trees and shrubs before the seeds ripen and drop or are carried away by wind or birds. You can remove the roots as time permits.