Invasive Species in Your Landscape

As gardeners continue to expand their landscapes with a desire for new plants with a variety of colors, shapes and textures, non-native plants increase in popularity. 

Native vs. Non-native Plants

Native species are those that occur naturally in each environment. But, non-native species are not necessarily invasive. Many non-native or exotic species are suited for different climate conditions and may need human care and intervention through temperature, watering, cultivation or pollination in order to thrive. However, some plants adapt or naturalize to their new environment and thrive in the absence of limiting factors, such as wildlife consumption or plant competition. Thus, their growth spreads, damaging the natural ecosystem. The loss of native plant species harms native wildlife and pollinators as they are often unable to quickly adapt to the changes in plant life and may lose the source of their food or shelter.

For practical purposes, non-natives have also been introduced for erosion control, as food sources for humans and livestock, for medicinal purposes, and to create wildlife habitat. Some plants also have been introduced accidently. Trouble arises when these plants become invasive, easily reseeding or spreading, taking over the garden and nearby areas. Kudzu (Pueraria montana var. lobata) is one example of an ornamental that was introduced and promoted as a forage crop and to control erosion. However, it grows alarmingly fast, climbing trees and other plants and smothering them. Kudzu now covers many areas of the Southeast. 

Often seeds of invasive species can be carried by wildlife, such as birds or small mammals, increasing their distribution. Japanese barberry (Berberis thunbergii) was introduced to the U.S. as an ornamental. Unfortunately, it forms a dense thicket, crowding out other native plants in the forest floor, and its seeds are easily spread by birds. Exotic plants also may leaf out earlier than native species, creating a canopy or forming dense vegetation that prevent light penetration to other plants in the area. English ivy (Hedera helix) was originally imported as an easy-to-grow ground cover. However, the aggressive-spreading vine blocks light from most other plants in its path, including killing large trees as it prevents their ability to complete photosynthesis. English ivy spreads both by vegetative reproduction and by seeds, ensuring that it easily propagates.

English ivy quickly consumes everything in its path.

Classifying Invasive Species

By definition, plants become invasive when their introduction to an ecosystem is likely to cause environmental harm to human, animal or plant health. The West Virginia Division of Natural Resources categories invasive species by the severity of their threat level. 

Level 1 includes “highly invasive species” that exhibit the most invasive tendencies, disrupting the ecosystem processes and causing “major” alterations in plant community composition and structure. They establish readily and spread rapidly. 

Level 2 includes “moderately invasive species” that have a “minor” influence on the ecosystem, altering plant community composition and community structure in at least one layer. They may establish dominance in the understory without disturbing other layers and typically require disturbance once established. 

Level 3 includes “occasionally invasive species,” which generally don’t affect the ecosystem processes, but may outcompete one or more plant species. They typically establish in an area disturbed from either human or natural origin, such as construction, storms or fire. They typically spread slowly or not at all. Some plants are more invasive in some regions of the state or under certain environmental conditions than they are otherwise. 

Common Invasive Landscape Plants in West Virginia 

List courtesy of the West Virginia Division of Natural Resources.

Controlling Invasive Plants

Controlling introduced invasive plants may require increased management by home gardeners, including weeding, spraying or pruning. Any approach should include integrated pest management practices, which involve a combination of management techniques to suppress the weed in effective, economical and environmentally-sound ways. Failure to prevent the spread of invasive species can lead to replacement of native vegetation, loss of wildlife food sources, wildlife habitat loss, vegetative monocultures when a single species dominates, and other issues when waterways are affected by invasive vegetation. A gardener’s first defense against invasive plants is to avoid planting them in the area to begin with. When purchasing landscaping plants and seeds, research each species or variety and consider its invasive threat level. Evaluate whether another plant might serve your purpose with a lower threat of invasion. 

Once an invasive plant is established, mechanical removal may require physically cutting, pulling or digging up the plant and/or its roots. Chemical methods may be used to kill plants and inhibit regrowth. Before attempting chemical or physical control, make sure you have accurately identified the plant species and chosen the best control method(s). Contact your local WVU Extension office for assistance with identification and control, if needed. Ensure you are properly protected with personal protective equipment (PPE) whatever control method applies.

Pesticides for Control of Invasive Plants

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