Controlling Invasive Plants
by Leonard Perry
by Leonard Perry


In extension I serve as an advisor and consultant to the greenhouse and nursery industry, primarily in Vermont but throughout the region and beyond as well.

I give presentations on my research to the industry, and to home groups. In Research, my focus is "herbaceous perennial production systems".

His website is at  Leonards zone of gardening: home with my trials, generally USDA 4a. Campus in Burlington is 5.

October 1, 2017

Invasive species, and in this case plants, continue to garner recognition from a number of publications, websites, and organizations. These plants are ones not native to a particular site, and which gain a rapid foothold once there, to the detriment of the native plants and fauna. These do not include the many introduced plants which are well behaved where planted.

While invasive plants are mainly spread by their seeds, often by birds, it is humans that, for the most part, originally inadvertently introduced them. And it is humans that can control them, as well, through various strategies.

Invasive plants, once in a better climate or without the pressures in their native habitats from feeding and diseases, outcompete native plants for resources such as light and water. These native plants, or naturalized ones such as many of our wildflowers, are not only attractive but also serve as food for animals and insects. These insects might be butterflies, or ones eaten by birds and that make up the main part of their diet.

Invasive plants of course weren’t introduced by humans for their harm and spread, with many years before their behavior in a new country or locale was noticed. Some were introduced for ornamental properties, such as the Norway maple from Europe in 1756. The first record of it “occasionally escaped” was not until the early 1900’s. Other plants we now consider invasive were introduced for function, such as for medicines, fence rows, cattle fodder, or erosion control. Others just secretly hitched a ride on pet fur, clothing, and in the ballast of ships.

Invasive plants can be grouped several ways. There are the ones currently planted as ornamentals (such as barberries), or those growing in the wild (such as purple loosestrife). Another grouping is by behavior, such as invading through spread of roots (as Japanese bamboo) or by seeds (such as buckthorn). Another grouping is by habitat, whether invasive on land (terrestrial, such as bush honeysuckle) or in water (aquatic, such as watermilfoil).

Here are ten suggestions on how you can help your local environment through decreasing invasive plant populations.

*Get familiar with what plants are invasive. Use state lists such as from Departments of Natural Resources or Conservation; lists from agencies such as the Nature Conservancy; and online sites such as from the New England Wildflower Society (

*If you find you have ornamental invasive plants in your landscape, plan to replace them with alternatives. Many state universities, master gardeners, or nursery groups have such lists, as does the U.S. National Arboretum (

*If you have root invasive plants, be careful where you dump roots when weeding as they can become established in fields and natural areas. Place such plants in plastic bags and dispose of properly.

*If you don’t have ornamental invasives already, plant alternatives instead. Watch plant sales or “gifts” from neighbors. Sometimes plants that spread aggressively are easy to divide and so get spread around unknowingly.

*Get familiar with the main wild culprits in your area, in woods, fields, and along roads. Learn how to identify them, being aware that other wild plants may look quite similar. The Invasive Plant Atlas for New England ( ) is a good such resource for that region. *Once you learn to identify invasive wild plants, learn when they seed, as this is the main means of dispersal. Be careful to avoid spreading seeds with ATVs, mountain bikes, shoes, or pet fur.

*Determine the best control strategy. Many control wild invasives by digging. If they are large or woody, repeated cutting often weakens them. Don’t cut or mow when they’re seeding, which is a main means of spread along roads. Encourage town road crews to mow early in season if possible. If using herbicides, do so according to the label and on one’s own property, as on other property most states require supervision by certified applicators. Many consider the Nature Conservancy handbook a good resource for controls (

*Tread lightly. In the zeal to rogue invasives don’t end up trampling the wildflowers and plants you are trying to help!

*More fun is in numbers, so consider joining “removal’ or conservation groups. Some of the already mentioned resources are a good starting point for contacts, as well as the National Agriculture Library website on invasive plants (

*Realize that you won’t eradicate all, so focus on the main sensitive areas, the ones where there are many wild plants and wildflowers, especially endangered ones. When choosing where to begin, some apply the Bradley Method originally developed by an Australian of this name. The first principle of this method is to begin in undisturbed areas, working towards those heavily infested with invasive plants. Weeding native stands gradually allows these plants to get further established, and move into adjacent areas as they are cleared. Also this method advocates disturbing the ground as little as possible, to deter weed seeds from germinating, and to not over-clear an area but to do so only as needed. This method emphasizes manual over chemical controls and patience, creating conditions for native plants to return over time.

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