Avoid growing these non-native invaders if you can
Love them or hate them, invasive trees are as much a part of the Austin, Texas landscape as the people from other states who have recently moved here. But, unlike our human neighbors, who are mostly just nice people jamming up MoPac, invasive plant species costs the U.S. an estimated $137 billion each year. When it comes to invasive trees, there are no legal restrictions on their sale and distribution. So they’re easy to buy from nurseries without the gardener ever knowing. Knowing which trees are invasive will help you avoid them and instead make a positive addition to Austin’s tree canopy.
Introduced as an ornamental tree in the late 1700s, Chinaberry trees have been in the nation longer than most of our ancestors. Unfortunately, the tree arrived without any of its natural enemies (pest or disease.) That’s why it was able to grow unchecked wherever it was planted. Wherever chinaberry grows, it takes over, displacing native species. Removal takes persistent effort and may require chemicals.
Another early arrival to the U.S., Americans imported Chinese tallow trees as a source of oil for the soap industry. This tree spreads rapidly and is capable of transforming an area into a tallow forest–eliminating native species. Both manual and chemical methods are necessary to control its spread.
Golden Running Bamboo
Bamboo, often planted in backyards as a screening device, is one of the most infestation-forming invasives. Besides taking over landscapes, bamboo leaf litter disrupts aquatic food webs. Even worse, it attracts roaches in backyards. Plant with caution, installing a barrier three feet deep to prevent spreading. You can control its growth by cutting back bamboo at ground-level often.
Lilac Chaste Tree
The same qualities that make the lilac chaste tree such an attractive landscape plant in Texas also make it a noxious invasive. It can grow in any soil and doesn’t mind heat or drought. While its blooms are fragrant and stunning, it seeds profusely. Its offspring take over areas where they establish and out-compete native species. You can control its spread by cutting the tree back to a few inches every year to maintain it at shrub-size.
This tree’s delicate, visually-pleasing profile and suffocatingly sweet blossoms tempt many in Austin to include it in their yard. But what looks like an innocent tree, is a monster in disguise. This short-lived, messy tree is susceptible to a wilting disease and prone to reproduce where it is least wanted. That’s why you see many along waterways and in abandoned lots. The best policy is never to plant a mimosa on your property.
Once used as an ornamental and shade tree, and now that we know better, it’s too late. Fast-growing paper mulberry grows to a height of 45 feet but is weak-wooded and shallow-rooted. It often blows over during storms, damaging homes and cars. It also spreads far and wide, displacing native plants. Never plant a paper mulberry, and if you have an ancient one in your yard, consider having it removed before it comes crashing down.
Both Japanese and Chinese privet species were introduced to the U.S. in the 1700s as hedge and garden plants. As we see in other invasive species, they easily escape cultivation and run amok in native landscapes. In fact, the privet has proven so invasive that volunteers regularly prowl Austin parks on search-and-destroy missions, ripping out glossy privets wherever they’re found. Controlling privet is possible through mechanical and chemical means, but the best policy is to avoid planting them in the first place.
(Photinia x fraseri)
Photinia comes in many varieties, all Asian in origin and all invasive. Their glossy evergreen leaves add visual appeal, but when they spread, they wreck ecosystems by crowding out the natives. Aside from their invasiveness, they’re also prone to a leaf spotting disease and may give your property a dated look. You can remove them by hand when young or cut to a stump.
Tree of Heaven
The name sounds divine, but this rapidly-growing tree (pictured at top), is closer to a devil when it comes to its ability to take over a natural area. Imported as an ornamental shade tree and prized for its ability to grow under poor soil conditions, it can now be found in at least a third of the United Statesf. Able to reach heights of 70 feet, ailanthus happily grows out of cracks in concrete, edges of forests, and anywhere a seed can find room.
Dr. Morgan Treadwell, assistant professor, and Extension Range Specialist at Texas A&M University, cautions against planting invasive species. “These plants not only disrupt the food web…but have become invasive pests that degrade habitat in remaining natural areas,” Treadwell says. She urges homeowners to look for native plants that are well-adapted, compete with weeds, and require little irrigation. When choosing trees for your yard, you also need to consider the hardiness zone, amount of light, and soil type. For a comprehensive list of native alternatives to invasive exotic plants, check out the City of Austin’s free guide “Native and Adapted Landscape Plants.”