Understanding the Dangers of Invasive Plants
Containing the Garden
Careful curation of a property’s landscape is essential to prevent invasive species from being introduced into local areas by spreading from yards into unmanaged and wild environments. In this article, we’ll go over what invasive plants are, how they spread, what negative effects they can have on ecosystems and human communities, as well as how to get rid of them, prevent their establishment, and manage the spread of those invasives already present.
What to Know About Invasive Plants
What Is an Invasive Plant?
An invasive plant is one that is not native to the location where it has been planted and whose spreading causes problems for the local ecosystem. Not all non-native plants are invasive, but those that spread uncontrolled will out-compete native plants and overtake an area, particularly in unmanaged environments.
There are a few reasons that invasive plants may spread from one yard to other yards and wild spaces. Those plants with the highest potential are:
Prolific seeders, whose seeds are distributed by wind and wildlife
Fast growers, growing earlier and more quickly than native plants
Dense growers, taking up lots of space and casting shade
Hardy varieties, able to grow in many conditions, including on both fertile and degraded land
How Do Invasive Species Get Introduced?
Invasive species are generally introduced by accident, either by someone who isn’t aware of their invasive potential or through unintentional transport. The main ways an invasive plant species finds its way into a foreign ecosystem include:
Being planted for ornament in gardens
Being planted for functional purposes, like soil stability
Being spread by international trade in shipping containers, natural resources, or manufactured products (such as seeds being caught in fibers or textiles)
Accidentally hitching onto vehicles like cars, trucks, or boats
How Do Invasive Plants Affect Ecosystems?
Invasive, non-native plants don’t align with the energy of a foreign space, growing faster than native species and causing a host of resulting problems for local ecosystems. Invasive plants cause important issues because they:
Compete with native organisms for limited resources such as nutrients, moisture, light, and space
Reduce plant diversity in an area by suppressing native growth
Encourage soil erosion and reduce flood control when native root systems are disturbed or removed
Affect food sources for native wildlife by suppressing the growth of leaves, berries, nuts, and other foods that native animals like insects (including important pollinators), rabbits, deer, and birds rely on
Affect whole food webs by impacting food sources for both herbivores and carnivores
Remove habitats for native insects, birds, and mammals by preventing the growth of trees, bushes, and other protected spaces where they live
By crowding out native plants and wildlife, invasive plants can lead to a decline in populations or even the extinction of local and specialized species, resulting in significant disturbance and degradation of ecosystems.
How Do Invasive Plants Affect Humans?
When an environment’s ecosystem is disturbed, damaged, or infested, it will impact the people who live there as well. Invasive species impact human communities in various ways:
By crowding out native plants, fewer beneficial ecosystem services are performed that humans depend on for comfortable living environments
Disruptions in ecosystems have economic effects, including degraded property, disrupted pollination of landscape plants and food crops, or, in the case of waterways, commercial movement
Public health issues may arise when a local food web is significantly disrupted (unbalancing insect, bird, mammal, or aquatic populations) or water quality is degraded, both of which may lead to the spread of disease
Invasive plants that degrade ecosystems affect our sense of “existence value,” the good feeling we get from knowing that something exists, like an animal population, an integral environment, or a natural resource
Invasive species have real dollar expenses when dealing with them, such as the costs of removal of plants and trees, physical damage to property, or losses due to reduced productivity or availability of a resource
Invasive plants also affect recreational possibilities: when preserves, parks, bodies of water, or waterways are overrun or disturbed by invasive plants, the beauty and accessibility of these environments are degraded or disrupted
Waterways that are degraded by invasive plants affect commercial or recreational navigability
The effects of invasive plants are most impactful in wild areas or very large properties, where it’s more difficult to control the appearance and spread of a foreign plant. The best way to reduce their impact is for property owners not to plant these species in the first place and remove them when they become aware of their presence.
Examples of Invasive Plants
When it comes to identifying an invasive species, it’s important to know what to look for. One major way of noticing an invasive species is by its unbound growth pattern: the single species will grow densely and in widespread patches over an area, crowding out other plants.
The best way to tell if a plant is invasive is by identifying it, either with an app on your phone or by learning what both the good local natives and the destructive invasives look like.
There are lists of invasive plant species held by state and federal governments, as well as local nature organizations. While some of these plants may be sold in nurseries and garden stores, a knowledgeable gardener or landscaper can avoid purchasing and planting these species. Some of the main offenders include:
Callery or Bradford pear tree (Pyrus calleryana)
Chinese privet (Ligustrum sinense)
Tree of heaven (Ailanthus altissima)
Princess tree or Paulownia (Paulownia tomentosa)
Mimosa or silk tree (Albizia julibrissin)
Norway maple (Acer platanoides)
Chinese and Japanese wisteria (Wisteria sinensis and Wisteria floribunda)
English ivy (Hedera helix)
Bush honeysuckle (Lonicera maackii)
Kudzu (Pueraria montana)
Invasive trees, like the Bradford pear or Chinese privet, were planted as ornamentals, but their weak branches and low nutritional or habitat value for wildlife make them poor and potentially dangerous choices for residential yards, from which they aggressively spread into unmanaged wilderness areas and onto large properties. Invasive vines grow over the ground and onto trees, crowding out and suffocating other plants. When vines grow on trees, they girdle the trunk and add extra weight onto branches, weakening those trees and creating a hazard.
Every state has lists compiled by various organizations that inform residents of the most present and troublesome invasive plants in the area. The Tennessee Invasive Plant Council has a list of invasive plants that are known for causing problems across the state, while the State of Tennessee has its own list as well.
How to Prevent Invasive Plants From Establishing
Homeowners and landowners can control what is planted on their grounds, but sometimes an invasive finds its way onto a property by wind or animal. Invasive plants can be managed in one of many ways depending on their stage of establishment:
Awareness: knowing what to look for and which species to avoid planting
Monitor: keeping an eye out for random, volunteer growth of invasives
Control: taking action right away to remove invasive plants when they are noticed
The more time a plant has to spread, the faster and more extensive its reach will be, which is why it’s important to act quickly when an invasive species is recognized. Early action is both easier and cheaper than waiting until it’s a widespread problem.
How to Get Rid of Invasive Plants
Once an invasive species is established, it can take years to remove it fully, costing time, attention, manpower, and dollars to fund and perform the maintenance activities. There are both physical and chemical options to remove an invasive plant species, and the best option will be based on the type of plant and the extent of its growth.
It's most important to remove a plant’s root system, which can regrow and spread further if left unattended. Cutting down a tree or vine can be followed up in one of a few ways:
Manually dig out the root system
Leave the roots, but cut back the shoots of new growth every couple of weeks to exhaust the root system (this is how deer kill new plants: by eating new shoots until the roots can’t produce any more)
Use an herbicide application to the freshly cut stump, carefully painting it on the open stump
Some invasive plants, like grasses, can’t be removed by hand. In the case of small patches, covering the area with a tarp and preventing sunlight from reaching the plant can kill it. In other cases, chemical control may be necessary. Contacting a professional such as a certified arborist or landscaper specialized in invasive plant removal is another option to get an invasive plant under control and learn which practices would be best for the long-term management of your particular situation.
The Future of Invasive Species Control
Removing and preventing the establishment of invasive plants is important to allow native plants and wildlife to thrive and avoid the many negative consequences that can follow the spread of invasive species. As climates warm, populations increase, and international trade continues, there is more and more opportunity for invasive species to be brought intentionally or accidentally. In the future, it will continue to be important to control the establishment of known and yet-to-be-problematic species of plants. Some tactics in the overall strategy include:
Monitoring environments, both big and small, for uncontrolled growth of non-native plants, both known and new, by citizens and organizations
Rules and laws prohibiting the sale, distribution, and import of problematic species
Rules about the cleanliness of boats that may spread invasive water plants
Nature-based suppressive techniques to manage invasive species
Research and development of specialized herbicides
General management and maintenance of ecosystem health to resist non-native species
Choose Native Plants for Your Property
For every beautiful non-native species, there is an equally beautiful native plant that will meet your desires while being in tune with the local ecosystem. This will result in much more beauty and harmony in gardens, landscapes, and wildernesses than a non-native species could ever create!
Organizations (both nonprofit and private) exist to help landowners control invasive species on their property. Weed Wrangle, for example, operates nationally to help organize group events to remove invasive plants from public spaces. If you have an invasive plant issue on your private property, businesses such as Invasive Plant Control exist to help you control invasive plant populations on your property.
For a selection of native and non-invasive trees you can plant in your yard without issue, browse our annual tree sale, open from October through February. If you’d like to help take care of our neighborhood canopy, you can volunteer with us! And for regular emails containing news and information about trees in Nashville, subscribe to our newsletter.