Most of us gardeners assume that the people that run our local garden center are knowledgeable and know exactly what they’re selling – and for the most part, that’s true. But what happens when some of the most commonly sold plants also happen to be some of the most invasive?
Due to the globalization of our society, it’s become very easy to get plants from different areas of the world, grow them, and sell them to gardeners everywhere.
Here’s a list of 20 of the most commonly sold invasive species. Watch out for them next time you’re browsing for a new plant for the yard!
Wisteria sinensis (Chinese wisteria)
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It was introduced from China to Europe and North America in 1816 and has secured a place as one of the most popular flowering vines for home gardens due to its flowering habit. It has however become an invasive species in some areas of the eastern United States where the climate closely matches that of China.
It can displace native species. Sizable trees have been killed by vining wisteria. When these large trees are killed, it opens the forest floor to sunlight, which allows seedlings to grow and flourish.
Phyllostachys spp. (Bamboo)
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Bamboo, which technically is a giant grass, is one of the world’s most invasive plants. Once established, it is literally next to impossible to control. The sprouts that shoot up from the ground each spring can grow 12 inches a day!
The underground roots of common running “fishpole” bamboo, which can easily reach 15 feet tall, can travel as far as 20 feet or more from the original clump.There’s no denying bamboo makes a pretty exotic screen. And with its slender form, it is seemingly ideal for tight urban spaces. Yet, in no time new shoots will appear outside its planting space, creating a maintenance nightmare.
Euonymus fortunei (Winter creeper/Creeping euonymus)
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This shade tolerant plant forms in dense mats, depriving native species of space and sunlight. Winter creeper will also deplete soil nutrients and moisture from nearby plants, making growth and regeneration harder on the native species. The invasive plant colonizes by vine growth and its pink-capsulated seeds spread by birds, small mammals, and water.
If allowed to grow out of hand, the vine will spread over anything in its way, even overtopping trees. The winter creeper’s rapid growth, evergreen nature and tolerance of harsh conditions allowed it to easily escape cultivation and quickly spread to forests in every county of the state.
Hedera helix (English ivy)
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English ivy is a vigorous growing vine that impacts all levels of disturbed and undisturbed forested areas, growing both as a ground cover and a climbing vine. As the ivy climbs in search of increased light, it engulfs and kills branches by blocking light from reaching the host tree’s leaves.
Branch dieback proceeds from the lower to upper branches, often leaving the tree with just a small green “broccoli head.” The host tree eventually succumbs entirely from this insidious and steady weakening. In addition, the added weight of the vines makes infested trees much more susceptible to blow-over during high rain and wind events and heavy snowfalls.
Lonicera japonica (Japanese Honeysuckle vine)
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In North America, Japanese honeysuckle has few natural enemies which allows it to spread widely and out-compete native plant species. Its evergreen to semi-evergreen nature gives it an added advantage over native species in many areas.
Shrubs and young trees can be killed by girdling when vines twist tightly around stems and trunks, cutting off the flow of water through the plant. Dense growths of honeysuckle covering vegetation can gradually kill plants by blocking sunlight from reaching their leaves. Vigorous root competition also helps Japanese honeysuckle spread and displace neighboring native vegetation.
Euonymus alatus (Winged Burning Bush)
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It threatens a variety of habitats including forests, coastal scrublands and prairies where it forms dense thickets, displacing many native woody and herbaceous plant species. Hundreds of seedlings are often found below the parent plant in what is termed a “seed shadow.”
There are two types available, the “old fashioned” or winged variety and the newer variety, Euonymus Alatus Compacta. The latter one is sold in nurseries and garden centers and does not spread and is not invasive. You can tell the difference between the two by looking at the stems. The older, invasive variety has “wings” on the stems, while the newer one does not. before buying these shrubs, check the stems to make sure of what you’re buying.
Nandina domestica (Nandina/Sacred Bamboo)
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Nandina has naturalized and invaded habitats. It colonizes by spreading underground root sprouts and by animal-dispersed seeds. It can persist as a seedling for several years before maturing. It can displace native species and disrupt plant communities. Berries are can be toxic to cats and some grazing animals.
Ligustrum sinense (Chinese privet)
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Privets form dense thickets that shade out and take the place of native shrubs and herbaceous plants. The shady thickets make conditions unsuitable for native seedlings. Phenolic compounds in the leaves protect plants from leaf-feeding insects which include native herbivorous species.
Elaeagnus umbellata (Autumn olive)
Source: 66 Square Feet
It threatens native ecosystems by out-competing and displacing native plant species, creating dense shade and interfering with natural plant succession and nutrient cycling. It can produce up to 200,000 seeds each year, and can spread over a variety of habitats as its nitrogen-fixing root nodules allows the plant to grow in even the most unfavorable soils. Not to mention that it reproduces quickly and with little effort at all.
Pyrus calleryana (Callery/Bradford pear)
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The Callery pear is an invasive species in many areas of eastern North America, outcompeting many native plants and trees. In the northeastern United States, wild Callery pears sometimes form extensive, nearly pure stands in old fields, along roadsides, and in similar disturbed areas.
Vinca minor (Common periwinkle/Vinca)
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Periwinkle grows vigorously and forms dense and extensive mats along the forest floor, displacing native herbaceous and woody plant species. While its purple flowers are quite striking in a large stand, this is usually a sign that this plant needs to be removed for the safety of local wildlife.
Berberis thunbergii (Japanese Barberry)
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Japanese barberry forms dense stands in natural habitats including canopy forests, open woodlands, wetlands, pastures, and meadows and alters soil pH, nitrogen levels, and biological activity in the soil. Once established, barberry displaces native plants and reduces wildlife habitat and forage.
White-tailed deer apparently avoid browsing barberry, preferring to feed on native plants, giving barberry a competitive advantage. In New Jersey, Japanese barberry has been found to raise soil pH (i.e., make it more basic) and reduce the depth of the litter layer in forests.
Paulownia tomentosa (Princess tree/Royal Paulownia)
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Princess tree is an aggressive ornamental tree that grows rapidly in disturbed natural areas, including forests, streambanks, and steep rocky slopes. It can survive wildfire because the roots can regenerate new, very fast-growing stems. It is tolerant of pollution and it is not fussy about soil type. All of these characteristics make it s very noxious and opportunistic invasive.
Clematis ternifolia (Sweet autumn clematis)
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This species is found invading forest edges, right-of-ways and urban areas along streams and roads. It grows vigorously over other vegetation, forming dense blankets that block sunlight to the plants underneath. In late summer infestations are conspicuous as a result of its abundant showy white flowers.
Eragrostis curvula (Weeping Lovegrass)
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The natural fire regime in desert communities has been altered as this species has increased, resulting in more intense wildfires that occur with greater frequency. It is not highly preferred by livestock and wildlife for grazing in comparison to native grasses, which has allowed it to become increasingly dominant in many native plant communities.
It establishes quickly, produces high quantities of viable seed during its first season of growth, and can spread at a rate of 175 m/year.
Spiraea japonica (Japanese spirea/Japanese Meadowsweet)
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Japanese spiraea can rapidly take over disturbed areas. Growing populations creep into meadows, forest openings, and other sites. Once established, spiraea grows rapidly and forms dense stands that outcompete much of the existing native herbs and shrubs. Seeds of Japanese spiraea last for many years in the soil, making its control and the restoration of native vegetation especially difficult.
Vitex agnus-castus (Chaste Tree)
Vitex is really a lovely tree that is sold in nurseries all over the US. They attract pollinators, and their flowers have been traditionally used as medicine. However, conservationists who focus on riparian areas and wetlands loathe this tree. Its seeds are spread easily by birds, who deposit them along streams and rivers, causing native plants to lose out on their foothold in the ecosystem.
Pueraria montana (Kudzu)
Much like English Ivy, Kudzu is a particularly dense thicket-forming vining plant. It tends to cover pretty much any area it’s planted. Forest edges, buildings, fences, and even abandoned vehicles are smothered by it as it grows rapidly, up to one foot per day. With how invasive this plant is, it’s wild that nurseries still sell it.
Alliaria petiolata (Garlic Mustard)
With leaves that smell like garlic when they’re bruised, and pretty white flowers, it’s disappointing to learn Alliaria petiolata is so invasive. In its second year of growth, the lovely flowers die back and the seeds are spread through an ecosystem by wind. They tend to populate in understories, outcompeting native plants through thicketing and shading. Their roots alter the microbiology of soil, pushing out native fungi and bacteria below the soil line.
Verbascum thapsus (Common Mullein)
Mullein is one of my favorite ingredients in teas as it tends to make my lungs feel good. However, the plant is a hugely invasive agent in pastures, ranch land, and meadows. Its prolific seeds tend to germinate easily in these areas and push out natives. Its taproot grows deeply into the ground as the plant matures, and it’s difficult to extract. Any unsuccessful attempts that result in a broken taproot are followed by another plant emerging from the root segment.
Frequently Asked Questions
Q: What are the 5 most invasive species?
A: This list identifies several. Japanese honeysuckle, knotweed, kudzu, privet, and wisteria are 5 of the top 10 most invasive plants sold at garden centers.
Q: What are successful invasive species?
A: Invasive species that manage to take over an ecological niche are considered “successful”. Unfortunately their success means the destruction of native habitats.
Q: What is the most successful invasive species?
A: Kudzu is probably the most successful on this list, and one of the most successful plant species in the world. They cover almost any structure, including other plants and trees, and slowly girdle them. This kills living plants and trees.
Q: What is the most common invasive plant?
A: Simply because of its beauty and ease of care, English Ivy is the most common. You’ll find this plant in landscaping across the US. Taking this one out can be quite a chore.
Q: Are there any beneficial invasive species?
A: While they overall cause more harm than good, Vitex and Japanese honeysuckle both support the diets of certain pollinators and birds.
Q: What state has the most invasive species?
A: Because of its temperate nature and diversity of species, Florida has the most invasive species of any US state.
Q: Are invasive species harmless?
A: If only they were! They tend to cause harm to the local ecosystem, change soil compositions, and cause difficulties in local waterways. Both wildlife and humans suffer as a result.
Q: Why invasive species are so successful?
A: Invasive plants tend to be so well-suited to an environment, they spread and take over, pushing out native plants, which support the health of wildlife and humans.
