An invasive species, as defined in an Executive Order signed by President Clinton in 1999, is an “alien species whose introduction does, or is likely to, cause economic or environmental harm, or harm to human health”
Some kinds of plants, due to being transplanted away from their natural home, consequently become invasive in their new home. That is, in the absence of their natural competitors, diseases and predators from back home, they spread uncontrolled in their new environment, invading native habitats, and displacing native species. Invasive species compete directly with native species for moisture, sunlight, nutrients, and growing space. Invasive plant infestations can negatively impact native ecosystems, wildlife habitats, fisheries, farming, utility operations, property values, tourism and outdoor recreation. Some 42% of the Endangered and Threatened plant species in the United States are threatened by invasive species, and 18% owe their Endangered or Threatened status primarily to the impact of invasive species.
Invasive plants from other parts of the world now dominate millions of acres of forest, desert, prairie, and wetlands in the United States. It is estimated that invasive species in the United States cause $130 billion in economic losses each year. We spend over $100 million a year combating invasive wetland plants, and nearly as much controlling terrestrial invasives.
What makes a plant invasive?
Invasive plants have the ability to reproduce abundantly, usually by producing huge quantities of seed and/or by spreading aggressively on vegetative runners or rhizomes. The seeds of many invasive plants are distributed widely by birds, wind, or as is often the case, by unknowing humans. Invasive plants typically grow fast and tolerate a wide range of soil and weather conditions. Unfortunately, it is difficult to determine if an introduced plant will become invasive before it actually does.
Not all of our popular ornamentals from other lands become invasive. (Thank goodness!) But some do and, as responsible gardeners, we should be aware of which non-native plants to avoid and as a result how to deal with potentially invasive plants already in our gardens. Furthermore, before you buy a plant for your garden or yard, be sure it is not known to be invasive. Ask the nursery staff. Check the list of noxious weeds for your state. Many states prohibit the sale and cultivation of the worst invasive weeds. There are lists of invasive plants on the internet for every state. Therefore, replace any invasive plants in your garden with non-invasive alternatives, suggestions for which can be found on web sites that feature garden plants such as https://plants.ces.ncsu.edu/plants/plant-list and www.floridata.com.
For additional resources on Invasive Plants, please find links at the end of this blog.
Our picks for some of the worst invasive plant species in the United States:
Kudzu (Pueraria montana)
- The vine that “ate the South” smothers everything in its path
- USDA Zones 5-10
- Native to East Asia, primarily subtropical and temperate regions of China, Japan, and Korea
- Suggested replacement: Runner bean (Phaseolus coccineus); Crossvine (Bignonia capreolata)
Chinese wisteria (Wisteria sinensis)
- Rampant vines can smother trees and break branches with their weight
- USDA Zones 3-9
- Native to China in the provinces of Guangxi, Guizhou, Hebei, Henan, Hubei, Shaanxi, and Yunnan
- Suggested replacement: American wisteria (W. frutescens); Carolina jessamine (Gelsemium sempervirens)
Running bamboo (Phyllostachys spp.)
- Spreads rapidly by rhizomes, crowding all other plants
- USDA Zones 6-10
- Native to China
- Suggested replacement: Clumping bamboo (Bambusa spp.); Green Giant Thuja (Thuja ‘Green Giant’); Cryptomeria Radican
- (Cryptomeria japonica ‘Radicans’
Purple loosestrife (Lythrum salicaria)
- A beautiful flower that quickly dominates wetlands to the exclusion of native species
- USDA Zones 3-9
- Native to Europe, Asia, northwest Africa, and southeastern Australia
- Suggested replacement: Blazing star (Liatris spicata); Daylilies (Hemerocallis spp.); cardinal flower (Lobelia cardinalis)
Japanese honeysuckle (Lonicera japonica)
- An aggressive twining vine with pretty flowers that yield sweet, suckable nectar, it smothers native shrubs
- USDA Zones 4-10
- Native to East Asia
- Suggested replacement: Coral honeysuckle (L. sempervirens); Purple passionflower (Passiflora incarnata)
Japanese barberry (Berberis thunbergii)
- With the ability to grow in deep shade, barberry forms dense thickets and crowds out native plants in northeastern forests
- USDA Zones 4-8
- Native to Japan and eastern Asia
- Suggested replacement: Ninebark (Physocarpus opulifolius); Mrs. Schiller’s delight viburnum (Viburnum Obovatum ‘Mrs. Schiller’s Delight’)
Get information on identification, early detection, prevention, and management of invasive plants in the United States here: https://www.invasiveplantatlas.org/index.html
This comprehensive site provides links to regulations and lists of noxious and invasive weeds by state: https://plants.usda.gov/java/noxiousDriver
This one lists invasive plants in fire-adapted ecosystems in the US, with links to photographs, descriptions, and distributional information: https://www.fs.fed.us/database/feis/plants/weed/
This one provides descriptions of many of our most troublesome invasive plant species: https://www.invasivespeciesinfo.gov/plants/main.shtml