Invasive plants are plants which grow quickly and aggressively, spreading and displacing other plants. Invasive plants are usually introduced by people either accidentally or on purpose, into a region far from their native habitat. Invasive plants are often referred to as "exotic," "alien," introduced" or "non-native" species. In their natural range, these species are limited by environmental, pest or disease conditions, keeping these species in balance within their ecosystem. When introduced into an area where these limitations are absent, some species have the ability to become invasive. These are the species we are concerned about in conservation.
Recognition of the problem of invasive plants is growing, at the same time as damage to native ecosystems is mounting. Identifying invasive plants and understanding the potential damage they can cause is essential to stopping their spread and protecting native vegetation. Invasive plants tend to appear on disturbed ground. The most aggressive can actually invade existing ecosystems. Invasive plants are generally undesirable because they are difficult to control, can escape from cultivation, and can dominate large areas. In short, invasive plant infestations can be extremely expensive to control, as well as environmentally destructive.
A small number of native plants can become "weedy” meaning they become aggressive after the landscape is altered. But the fundamental condition here is the disturbance of the habitat that upsets the balance. This is not true “invasiveness”.
The tabs below provide a library of information about troublesome trees, shrubs, vines, herbs and aquatic plants that have impacted the state's natural lands and suggest actions you can take to protect your property from invasive plants. This list is non-regulatory in nature. The species listed here are considered invasive by DCNR staff and are managed for accordingly.
What Can I Do About Invasive Plants?
The best insurance against future problems is to avoid the use of known invasive plants and educate others about the problems of invasive species. This website lists many of the plants that are considered invasive in Pennsylvania. Plants on this list should not be used around your home or community because they can escape cultivation and aggressively move into surrounding ecosystems. Avoid invasives by choosing plants that are native to your area. Natives often are adapted to a specific environmental niche, and have natural controls that keep them in balance.
Download DCNR's brochure Invasive Plants in Pennsylvania. This document summarizes features of many of Pennsylvania's worst plant invaders, discusses the issues involved, and provides a list of resources.
Minimize landscape disturbance. Invasive plants thrive on bare soil and disturbed ground where the native plant community has been displaced. The key to controlling invasives is to protect healthy native plant communities.
Use fertilizers wisely. Proper site preparation begins with a soil test before applying fertilizer. High nitrogen levels sometimes give an advantage to invasive species that are better adapted to using plentiful nutrients for explosive growth. For soil fertility, try using organic, slow-decomposing compost and mulches
Have a land management plan for maintenance over time. It makes sense when designing a property to plan for future maintenance. Lawns are maintained by weekly mowing, while gardens are often hand-weeded. Meadows in Pennsylvania may need to be mowed every year. Woodlands are probably the lowest-maintenance landscape, but they too will need to be monitored and invasive plants removed.
Scout your property annually for invasives or other problems. The best way to control invasives is prevention, and prevention can only happen through vigilance. Listed on this web site are resources to help property owners.
Remove invasives before they are a problem. Effective scouting or monitoring means that problems are found while they are still small and easily controllable. For instance, do not let invasive plants go to seed. Mechanical removal through digging or cutting is preferred. Large populations of invasives may need to be stopped chemically with spot applications of herbicide by trained individuals or by homeowners carefully following label instructions.
Replace invasive plants with native or noninvasive species. Invasives are good at exploiting bare soil and empty niches. When you remove an invasive plant, unless there is another plant substituted, the invasive will tend to come right back. What grows in the future depends largely on what is there now; so it is important to fill that niche with a desirable plant that will provide seed for the future.
Remove invasives as they appear while their densities are low. This gives the most immediate success because invasive plant control works best where there is a functioning native plant community still in place which can move right into the empty niche.