With mild winters, beautiful beaches, majestic mountains and friendly people, who would turn down the chance to visit the South? Unfortunately, some botanical visitors have overstayed their welcome and set down roots. For the following species, things that started off as a garden trial have turned into a forest invasion. These imported ornamentals have escaped the backyard and are now out-competing many of our Southern plants. As landscapers and gardeners, beware: These species aren’t just pretty – they’re prolific.
Chinese Tallow Tree
Perhaps none other than Benjamin Franklin himself sowed the first seeds of a Chinese tallow tree (Sapium sebiferum) in American soil. In 1772, he scribbled the following lines to a friend in Georgia: “I send also a few seeds of the Chinese tallow tree, which will I believe grow & thrive with you. 'Tis a most useful plant.” But even wise old Benjamin Franklin couldn’t foresee how well the Chinese tallow tree would, in fact, grow and thrive. Over 200 years later, this “most useful plant” is a noxious weed throughout much of the South.
Season temperature shifts cause Sapium sebiferum to display a beautiful array of colors. However, don't be fooled by its beauty. It is highly invasive with a single tree able to produce up to 100,000 seeds every year and remain productive for 100 years. 1
With unique diamond-shaped leaves and beautiful multi-colored fall foliage, it’s no wonder the tallow tree was a popular ornamental. Unfortunately, a single tallow tree can produce thousands of wax-coated seeds each year, which has led to its quick spread throughout Southern forests where it out-competes and displaces native species. Once established, the Chinese tallow tree is difficult to control in large areas, but herbicides and chainsaws are effective on a small scale. For ornamental planting, our native sassafras (Sassafras albidum) has equally beautiful fall foliage.
First introduced in the 1800s as an ornamental hedge, various cultivars of Chinese privet (Ligustrum sinense) still frequent garden centers and nurseries. Nevertheless, it’s much easier to find privet along roadsides and in woodlands, since long ago this exotic shrub escaped cultivation to become a major pest.
Chinese privet grows quickly from both root suckers and seed, and that, along with its small, evergreen foliage, are good qualities for a hedge. Unfortunately, privet thickets are commonplace in bottomland forests, where they offer little nutritional value to native wildlife. On a small scale, both mechanical and chemical controls of Chinese privet are effective. If using mechanical means, like mowing or cutting, dig up roots to prevent resprouting. For native alternatives, waxmyrtle (Myrica cerifera) and yaupon (Ilex vomitoria) are good choices.
During my childhood, honeysuckle grew up and down a chain-link fence in my backyard. I pulled stamen after stamen through the cream-colored petals to taste those single drops of nectar. Although coral honeysuckle (Lonicera sempervirens) is indeed native, when most people say “honeysuckle” they mean its invasive relative, Japanese honeysuckle (Lonicera japonica), the one that grew on my backyard fence.
Introduced in the early 1800s for dual purposes, Japanese honeysuckle provided a sweet-smelling fragrance for gardens and a fast-growing ground cover for hillsides. Like kudzu, Japanese honeysuckle was widely planted to prevent and alleviate erosion. However, the vine can literally choke the life out of native plants and leave behind a tangled mess instead. If you’re ever tempted to plant or propagate Japanese honeysuckle, remember our many beautiful native alternatives: coral honeysuckle (Lonicera sempervirens), Carolina jessamine (Gelsemium sempervirens) and crossvine (Bignonia capreolata), among others.
During the seasons of Thanksgiving or Christmas, you might find Oriental bittersweet (Celastrus orbiculatus) hanging on one of your doors or windows. With lots of orange and red berry-like fruit produced in the fall, Oriental bittersweet is a twining vine that crafters frequently weave into Thanksgiving and Christmas wreaths. The berries also find favor among birds, which help spread this invasive species. Like Japanese honeysuckle, bittersweet can choke and smother native trees and shrubs, and you'll often find it draped up and down forest edges.
Although yet to spread to the Deep South, Oriental bittersweet is a major problem in North Carolina, Tennessee and Virginia, especially in the mountains. Like many invasive species, bittersweet thrives in the full sunlight along roadsides, and each year it travels to new territory. To lessen its spread, be sure to check those wreaths before you buy them, and plant native alternatives like our native bittersweet (Celastrus scandens), trumpet creeper (Campsis radicans) or any natives mentioned above for Japanese honeysuckle.
Admittedly, Chinese wisteria (Wisteria sinensis) is strikingly beautiful and fragrant, and it’s easy to understand why it was introduced in the 1800s as an ornamental. As one of the first signs of spring, the purple and often ubiquitous flowers of Chinese wisteria seem nearly at home in Southern forests, but beneath those flowers are thick, heavy vines that can weigh down native trees, breaking trunks and limbs.
If you have Chinese wisteria growing on an arbor, consider replacing it with American wisteria (Wisteria frutescens), which blooms later, in July and August, but has equally beautiful purple-white flowers. As with many invasive species, Chinese wisteria can persist and resist control, but repeated cuttings of a wisteria vine near the ground should eventually deplete energy stored in the roots.
1 Fall trees public domain. Other two Chinese tallow photos CC BY SA 2.0 Tatiana Gerus.
2, 3 Photos courtesy of Stephen Bishop.
4 Photo by Leonora Enking. Inset photo by Esteve Conaway.
5 Photo by Hunter Desportes.