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The Gardener’s Battle: 50 Invasive Plants To Avoid In Your Garden

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If you love gardening, you’re no stranger to the challenges of managing persistent weeds like dandelions and nettles. However, it’s not just the typical weeds that demand attention. Certain ornamental plants can also become overbearing, overwhelming nearby vegetation.

You might already be familiar with some of the major invasive plant culprits, such as Japanese knotweed, Himalayan balsam, and Rhododendron ponticum. These plants are so aggressive that laws have been established to curb their encroachment into natural areas, where they pose a threat to local habitats.

Particularly notorious is Japanese knotweed, which can be so problematic that its presence in your garden might hinder your ability to secure or refinance a mortgage. Moreover, allowing it to spread to neighboring properties can lead to legal consequences.

Yet, there are other less-known invasive species that are still sold in many garden centers and used for their decorative appeal. While they’re not banned, you might want to reconsider adding them to your garden, especially if space is limited or you prefer a low-maintenance garden.

Dealing with these invasive species typically involves physical removal, such as uprooting by hand, or applying systemic herbicides. Both methods require persistence, often taking several years to completely eradicate the invaders. Staying vigilant and patient is crucial.

Table of Contents

What is an Invasive Plant?

Invasive plants are non-native species that can rapidly spread and invade areas where they are not desired. While they are not always unsightly and may even bear attractive blossoms, their unchecked growth can be problematic. Depending on the region, what is harmless in one area could wreak havoc in another by aggressively crowding out local flora.

Authorities at various levels—international, national, and local—often implement measures such as advisories, regulatory actions, and eradication efforts to curb the spread of these harmful plants.

Invasive species can inflict significant economic, environmental, and ecological damage. They compete with indigenous plants for essential resources like water and sunlight, threaten endangered species, degrade natural habitats, contribute to soil erosion, and displace vital food sources for native wildlife.

The introduction of invasive plant species into new environments typically occurs without the natural predators that keep them in check in their native habitats. Often originating from garden settings or brought in through nurseries and other plant vendors, these plants can quickly take over large areas, displacing local plant and animal life and altering ecosystems.

The impact of invasive plants is profound, costing billions annually in damages across the United States. As we deepen our understanding of these plants, it becomes clear how challenging they are to manage or eliminate.

Prevention is key—opt for native plants instead of known invasive varieties and familiarize yourself with invasive species in your region. Be proactive in reporting any sightings to local authorities and choose garden plants wisely, avoiding those known for prolific seeding or other invasive traits.

On the topic of controlling these plants, it’s important to note that not all invasive species require the same approach. For instance, the use of glyphosate-based herbicides varies in concentration depending on the product and the specific needs for effective control.

Products like Ortho Kleen-Up, Roundup Lawn and Garden, and others contain different percentages of glyphosate, tailored to handle various plant sizes and types at the time of application. Always refer to the product’s label for precise usage instructions.

Rebecca Sears from Ferry-Morse seeds emphasizes that the term “invasive” is location-specific and should not be confused with “aggressive,” which refers to native plants that spread rapidly within their natural range.

Understanding the difference and knowing which plants are considered invasive in your locality can help maintain a healthy, diverse garden environment. As invasive species expand, they not only suppress native plant growth but can be extremely difficult to eradicate due to their robust root systems and high seed production.

The U.S. Forest Service highlights that invasive plants are implicated in the decline of 42% of the U.S. endangered and threatened species. They pose a significant threat to plant diversity, impacting agriculture, water quality, recreational activities, and wildlife habitats.

Check out our comprehensive list of invasive garden plants for more details.

Giant Hogweed (Heracleum mantegazzianum)

  • Appearance: This towering plant can grow up to 15 to 20 feet tall, featuring massive leaves that span up to 5 feet across, paired with thick stems topped with clusters of white, umbrella-shaped flowers.
  • Risks: Living up to its grand size, giant hogweed is a real environmental bully, towering over and diminishing biodiversity. More alarmingly, it poses a health hazard as its sap is phototoxic, which can cause severe burns when it comes into contact with skin under sunlight.
  • History and Spread: First brought to the U.S. in the early 1900s as a garden novelty, it has since spread wildly, elbowing out native flora.
  • Human Impact: The plant’s sap is laden with harmful chemicals known as furocoumarins. Exposure to sunlight after contact with the sap can lead to severe skin inflammation and blisters, sometimes resulting in prolonged sensitivity to sunlight.
  • Removal Advice: Given its hazardous nature, removing giant hogweed is a task for professionals. Reach out to local agricultural experts for safe eradication.
Giant Hogweed
Credit: Invasive Species Centre

Mimosa Tree (Albizia julibrissin)

  • Appearance: This tree is easily recognized by its fern-like leaves and soft, pink, feather-like flowers that are a magnet for pollinators. It’s a common sight in the southern U.S.
  • Risks: Known as the silk tree, this invasive species, originating from Asia in the 1700s, is a vigorous grower that outpaces local flora, disrupting the local ecosystem. It’s particularly harmful to native species that are crucial for the diet of local wildlife. Moreover, its seeds are toxic to dogs.
  • Removal Tactics: To control its spread, cut the tree down to ground level. Be vigilant about removing any new growth promptly. Seedlings should be pulled out by hand.
Mimosa Tree (Albizia julibrissin)
Credit: Wikipedia

Chinese Wisteria (Wisteria sinensis)

  • Appearance: This vine is known for its ability to wrap around trees, showcasing clusters of aromatic lavender flowers each spring.
  • History and Intrusion: Originally from China and introduced to the West in 1816, Chinese wisteria was celebrated for its beauty but soon became an aggressive invader in certain U.S. regions.
  • Environmental Impact: It’s notorious for strangling trees with its robust growth, potentially leading to their death. This disruption can radically alter local ecosystems.
  • Preferable Alternatives: For those charmed by wisteria, opt for the native American wisteria (Wisteria frutescens), which is non-invasive yet equally stunning.
  • Removal Tips: Cutting the vines is a start, but persistent and possibly professional measures, like herbicides, might be required to completely halt its spread.
Chinese Wisteria
Credit: The Spruce

Lily of the Valley (Convallaria majalis)

  • Appearance: Lily of the Valley boasts slender, sword-like leaves and delicate, sweet-smelling bell-shaped flowers that bloom in late spring, making it a favorite for wedding arrangements.
  • Challenges: Despite its charm, this plant can rapidly overtake gardens. It spreads through seeds and rhizomes, forming dense patches that outcompete local flora. In some areas like Wisconsin, it’s classified as invasive due to its aggressive growth.
  • Control Methods: To control Lily of the Valley, you’ll need to thoroughly remove the rhizomes, ensuring even the smallest pieces are eliminated to prevent regrowth. Regular digging may be necessary for complete eradication. Alternatively, mowing the area can help prevent seed formation.
Lily of the Valley
Credit: Wikipedia

Tree of Heaven (Ailanthus altissima)

  • Appearance: This small tree features large, compound leaves with serrated edges, and clusters of yellow flowers in spring, followed by winged fruits.
  • Impact and Risks: Native to China, the Tree of Heaven is notorious for its rapid spread in urban and forested areas, often damaging pavements and building foundations with its robust root system. It releases chemicals that inhibit nearby plant growth and serves as a host for pests like the spotted lanternfly.
  • Removal Strategies: Young seedlings can be pulled by hand, but older trees require a more comprehensive approach. Cutting them down often leads to vigorous resprouting, so multiple methods, including herbicides, may be necessary for effective control.
Tree of Heaven
Credit: University of Maryland Extension

Norway Maple (Acer platanoides)

  • Appearance: Unlike typical invasive shrubs or weeds, the Norway Maple is a robust tree that can reach heights of 40 to 60 feet, with deep green, lobed leaves and a dense, shade-casting canopy that stifles undergrowth.
  • Invasiveness: Originating from Europe, this tree was once favored for its rapid growth and shade-providing canopy. However, its ability to produce copious seeds and spread widely has made it a problematic invasive in many regions, particularly in the Northeast U.S.
  • Management: Avoid planting Norway Maple if you’re looking for a new shade tree. If it’s already present, young saplings can be removed by hand or with tools, but mature trees might require professional removal. Cutting techniques and herbicide treatments, such as girdling or applying glyphosate to cut stumps, are effective ways to prevent further spread.
Norway Maple
Credit: New York Invasive Species Information

Explorer Sugar Maple Trees: Nature’s Gift to Farmers and the Environment

Japanese Honeysuckle (Lonicera japonica)

  • Appearance: Known for its lovely, sweet aroma, Japanese honeysuckle is a charming yet deceptive vine that can stretch up to 30 feet with yellow blossoms blooming from June to October. Initially planted for ground coverage, it’s now recognized as an invasive threat throughout the Midwest.
  • Concerns: Introduced in the 1800s for ornamental purposes, it quickly outpaces native vegetation, spreading rapidly through bird-dispersed seeds. If you’re set on honeysuckle, consider non-invasive varieties like the coral or trumpet honeysuckle (Lonicera sempervirens) instead.
  • Impact: With few natural predators in North America, it dominates local flora. Its semi-evergreen nature further gives it an advantage over native plants.
  • Management: To keep it under control in your garden, you’ll need to prune it aggressively. It can strangle trees and shrubs with its dense vines, which also block sunlight, slowly killing other plants through suffocation and root competition.
  • Control Tips: For sprawling, established vines, consider hand-pulling or mowing. Regular monitoring and cutting back will help manage its growth.
Japanese Honeysuckle
Credit: The spruce

English Ivy (Hedera helix)

  • Appearance: This vine features lobed or spade-shaped leaves and is known for rapidly scaling walls and trees.
  • Drawbacks: While the image of ivy-clad buildings is romantic, English ivy is an ecological nightmare. It smothers other groundcovers and can damage both buildings and trees. Introduced from Europe in the 1700s, it spreads quickly and aggressively.
  • Growth Habits: It’s an excellent choice for rapidly covering ground; however, its aggressive nature makes it a problematic invasive species, particularly in the Pacific Northwest.
  • Damages: As it climbs, it blocks light to the host tree, eventually killing it by suffocating and adding weight, which increases susceptibility to storm damage.
  • Removal Steps: If you need to remove English ivy, do it by hand and cut the vines at the base of the trees. Dispose of the vines with household trash to prevent further spreading.
English Ivy
Credit: wikipedia

Orange Daylily (Hemerocallis fulva)

  • Appearance: Often seen brightening up roadsides and old homesites with its vibrant orange blooms, this plant is affectionately known as the “ditch lily.”
  • Issues: Despite its beauty, the orange daylily is invasive, spreading through its robust tuber system. It was introduced in the 1900s and has since posed a threat to native plant species.
  • Alternative Choices: If daylilies are a must-have for your garden, opt for less invasive, hybrid varieties instead of the common orange type.
  • Eradication Method: To effectively remove this plant, excavate the entire tuber and root system to prevent regrowth.
Orange Daylily
Credit: American Meadows

Bradford Pear (Pyrus calleryana)

  • Appearance: This small, oval-shaped deciduous tree boasts vibrant white flowers each spring.
  • Downsides: Once a favorite among gardeners for its quick growth and spring blooms, the Bradford Pear is now less favored due to its invasive nature and the unpleasant odor of its flowers, which many liken to rotting fish. Additionally, its wood is brittle, making it prone to splitting.
  • Alternatives: For those seeking spring beauty, consider planting native species such as dogwoods or flowering crabapples, which are less invasive and just as stunning.
  • Removal Tips: To manage this invasive tree, cutting it down is recommended. Replacing it with native trees can enhance local biodiversity and provide beautiful spring colors.
Bradford Pear
Credit: wikipedia

Barberry (Berberis vulgaris, Berberis thunbergii)

  • Appearance: These dense, rounded shrubs feature small, oval leaves that come in shades of red, green, or burgundy, and are armed with sharp spines.
  • Issues: Originally introduced as ornamental plants, various types of barberry have become exceedingly invasive in the U.S., particularly Japanese and European varieties. They disrupt local ecosystems by forming dense thickets that alter soil chemistry and block native growth.
  • Wildlife Impact: Barberry shrubs provide a haven for deer ticks, raising concerns about Lyme disease. Their thick growth also discourages deer from feeding on them, giving them an advantage over native plants.
  • Control Measures: Removing barberry may require gloves due to its thorns, and can be done by hand-pulling or digging. Persistent control methods might be necessary for complete eradication.
Barberry
Credit: University of Maryland Extension

Poison Hemlock (Conium maculatum)

  • Appearance: With its deceptive beauty, poison hemlock displays fern-like leaves and clusters of small white flowers. It’s easily recognizable by its stout, purple-spotted stems.
  • Toxicity: This plant is dangerously toxic to both humans and animals, containing alkaloids that can be fatal if ingested. Mistaken identities with edible plants like wild carrots have led to serious poisoning cases.
  • Background: Introduced in the 1800s as an ornamental, this biennial quickly spreads by seeds and has become a significant problem in parks and gardens across the U.S.
  • Safe Removal: Due to its toxicity, removing poison hemlock should be handled with care. Small areas can be dug up wearing gloves. For larger infestations, professional help from local agricultural agencies is recommended to safely manage this hazardous plant.
Poison Hemlock
Credit: wikipedia

Japanese Stiltgrass (Microstegium vimineum)

  • Appearance: This invasive grass resembles miniature bamboo, reaching up to 3 feet tall. It has weak stems, aerial rootlets near the base, and 2 to 4-inch leaves with a distinctive whitish midrib.
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  • Problematic Nature: Japanese stiltgrass spreads rapidly across forest floors, forming dense mats that exclude other vegetation. Areas with high deer populations are particularly vulnerable, as deer prefer native plants, exacerbating the stiltgrass’s spread.
  • Control Strategies: For minor infestations, carefully hand-pull to prevent seed dispersal. Mowing late summer before the grass seeds can help control its spread. In widespread infestations, apply a systemic herbicide containing glyphosate.
Japanese Stiltgrass
Credit: North Carolina Extension Gardener Plant Toolbox

Kudzu (Pueraria montana)

  • Appearance: Kudzu is a fast-growing vine that can extend up to 100 feet with large, lobed leaflets, purple pea-like flowers, and hairy seedpods. It’s known for its remarkable growth rate, extending up to a foot per day in optimal conditions.
  • Concerning Impact: Nicknamed “the vine that ate the South,” kudzu envelops nearly any surface, including trees, fences, and buildings, blocking sunlight and outcompeting native species.
  • Management Techniques: Goats can effectively graze on young kudzu, potentially clearing an infestation in a few years. For mature plants, cutting back during summer heat followed by applying glyphosate to the roots or stumps has proven effective.
Kudzu
Credit: North Carolina Extension Gardener Plant Toolbox

Japanese Hops (Humulus japonicus)

  • Appearance: This vigorous annual vine can climb up to 35 feet in a season. It has lobed, toothed leaves covered in rough, skin-irritating hairs, and produces clusters of green, petal-less flowers followed by yellow-brown cones.
  • Impact on Ecosystems: Japanese hops climb aggressively over vegetation, forming dense thickets that block light and stifle plant growth beneath, killing young trees and preventing new plants from emerging, severely disrupting native ecosystems.
  • Tackling the Issue: For small areas, early season hand-pulling while wearing protective clothing can manage its spread. Larger infestations might require repeated mowing or applications of a glyphosate-based herbicide.
Japanese Hops
Credit: Trees Atlanta

Purple Wintercreeper (Euonymus fortunei)

  • Appearance: This evergreen ground cover has dark green, oval leaves (1 to 2 inches) marked by distinctive silvery veins. In summer, it blooms with small green-white flowers, and in fall, it showcases vibrant orange-coated seeds in red capsules. Variegated forms are also popular.
  • Impact: Extremely shade-tolerant, purple wintercreeper forms thick mats that overpower native plants by hogging sunlight and nutrients. Its robust growth, vine expansion, and wildlife-assisted seed dispersal make it a formidable invader.
  • Control: For lighter invasions, pull vines and roots by hand or dig them up, properly disposing of all parts. In severe cases, cut stems in autumn and apply a glyphosate-based herbicide directly to the cut ends.
Purple Wintercreeper
Credit: Greenwood Nursery

Reed Canary Grass (Phalaris arundinacea)

  • Appearance: A resilient perennial, reed canary grass stands 2 to 6 feet tall with blue-green stems and densely packed tiny green-purple flowers maturing to beige. Some varieties display striking green and white striped leaves.
  • Troublesome Nature: Known for rapid growth, reed canary grass dominates native grasses within months after planting. Its aggressive nature is compounded by its long history of cultivation and escape into the wild across North America.
  • Management: For small infestations, hand-dig or cut stems at flowering to prevent seeding. For larger areas, especially in wetlands, use a glyphosate-based herbicide to effectively control growth.
Reed Canary Grass
Credit: Ontario Invasive Plant Council

Crown Vetch (Coronilla varia)

  • Appearance: This perennial plant has sprawling 2 to 6-foot stems rising up to 2 feet high. It blooms from early summer to late fall with small clusters of pink and white pea-like flowers, followed by unique crown-like seedpods.
  • Concerns: Initially planted in the 1950s for erosion control, crown vetch has become pervasive, quickly overtaking large areas and proving difficult to eradicate.
  • Control Strategies: Crown vetch’s rapid spread and long-lasting seeds make it challenging to control. While glyphosate-based herbicides offer some control, using a 2% triclopyr solution and ensuring complete coverage is more effective.
Crown Vetch
Credit: Minnesota Department of Agriculture

Buckthorn (Rhamnus cathartica, R. frangula)

  • Appearance: Buckthorn is either a tall shrub or small tree, growing up to 25 feet with multiple stems from the base and a wide crown. It has gray to brown bark with a notable orange hue inside.
  • Problematic Nature: Native to Europe and Western Asia, buckthorn forms dense thickets that outcompete local flora due to its rapid growth. Its berries attract seed-spreading birds, exacerbating its spread. Additionally, it hosts harmful fungi.
  • Control Measures: For young seedlings, hand-pull when the soil is moist to prevent resprouting. For larger specimens, dig out or cover the stump with black plastic for two years after cutting. For those over 2 inches in diameter, apply a glyphosate-based herbicide to the cut stump.
Buckthorn
Credit: Invasive Species Centre

Chinese Privet (Ligustrum sinense)

  • Appearance: This evergreen shrub reaches up to 12 feet tall with rounded 2-inch leaves. In spring, it blooms with fragrant white flower clusters, followed by blue-black berries persisting into winter.
  • Problematic Nature: Introduced from China in the 1850s, Chinese privet quickly forms dense thickets that overshadow and displace native plants, particularly along waterways and roadsides. Its seeds spread widely by birds, and its shallow yet aggressive roots and allergenic pollen exacerbate the issue.
  • Control Measures: Hand-digging suits small plants with stems up to 1 inch in diameter. For larger plants, cut and immediately apply a glyphosate-based herbicide to the cut stumps during early winter to prevent regrowth.
Chinese Privet
Credit: Nashville Tree Conservation Corps

White Mulberry (Morus alba)

  • Appearance: A fast-growing deciduous tree reaching 30 to 50 feet, white mulberry has glossy green leaves of varying shapes. It blooms in spring with small yellow-green flowers, producing sweet blackberry-like fruits ripening to various colors from white to dark purple.
  • Problematic Nature: Brought from China in the 1600s as silkworm food, white mulberry has become invasive in many areas, displacing native species and threatening local red mulberries with disease. Birds widely eat and spread the seeds.
  • Control Measures: While hand-digging manages smaller trees, they can regrow from stumps and roots. For larger problems, apply a glyphosate-based herbicide to cut stems in fall, though long-term solutions are limited. Employing goats to browse the area annually has shown some effectiveness.
White Mulberry
Credit: Poison Control

Oriental Bittersweet (Celastrus orbiculatus)

Frequently topping the list of invasive plants in North America, Oriental bittersweet is a vine that can rapidly overtake woodland areas.

Its relatives, American bittersweet (Celastrus scandens) and bittersweet nightshade (Solanum dulcamara), also pose invasive threats, though to a lesser degree. The American variety is known for its eye-catching red and orange berries, commonly used in fall decorations.

Oriental Bittersweet
Credit: National Invasive Species Information center

Sweet Autumn Clematis (Clematis terniflora)

Originally from Japan, this plant is renowned for its charming appearance and sweet fragrance. However, it can aggressively spread across landscapes, particularly in the Eastern and lower Midwestern United States.

It smothers other plants by forming dense canopies that block sunlight, especially when it profusely blooms with white flowers in late summer.

Sweet Autumn Clematis
Credit: Cary Magazine

Bugleweed (Ajuga reptans)

Also known as ajuga, this ground cover is favored for its attractive purple flowers and ability to suppress weeds. While beneficial in shady areas, ajuga can become overly aggressive, particularly in warmer climates where it isn’t naturally controlled by winter frosts.

Bugleweed
Credit: The Spruce

Winged Burning Bush (Euonymus alatus)

This striking bush is notorious for its vibrant fall foliage and reddish-orange berries. Originating from Asia, it has become a problematic invasive across much of the northern U.S., from Maine to Minnesota and down to the Southeast. It forms dense thickets that displace native plants.

When shopping for these bushes, differentiate between the invasive ‘old-fashioned’ variety with winged stems and the non-invasive ‘Euonymus Alatus Compacta’. Checking the stem structure can prevent introducing an invasive plant to your garden.

Winged Burning Bush
Credit: Invasive Org

Lantana Camara 

Lantana camara, a vibrant evergreen shrub native to the tropics, thrives particularly well in warmer U.S. states like Florida and California.

Although celebrated for its colorful blooms and used in decorative hanging baskets in cooler climates, in zones warmer than 9, lantana can spread uncontrollably. In these regions, it easily escapes garden boundaries, potentially overtaking local flora.

Lantana Camara 
Credit: wikipedia

Butterfly Bush (Buddleja davidii) 

Commonly known as the butterfly bush, Buddleja davidii is a favorite in gardens for attracting butterflies with its nectar-rich blooms. Originating from China, this plant has a darker side in the Pacific Northwest and parts of the Southeast, where it mirrors its native conditions and becomes aggressively invasive.

Despite dying back in colder climates (below zone 6), in milder regions, it proliferates rapidly, pushing out native plants essential for local butterfly populations. For those looking to support butterflies without ecological risk, consider planting butterfly weed (Asclepias tuberosa) instead.

Butterfly Bush
Credit: wikipedia

Japanese Knotweed (Fallopia japonica) 

Japanese knotweed is notorious for its rapid spread and minimal aesthetic value, despite its fluffy white flowers that appear in early fall. This plant is widely regarded as one of the most problematic invasives, thriving in zones 5 to 9 and recommended for immediate removal wherever found.

Japanese Knotweed
Credit: wikipedia

Tansy 

Tansy, known for its rich history in medicine and cooking, also carries significant risks due to its toxicity and invasive nature. This herb aggressively spreads through seeds and its root system, posing a threat to large areas if not controlled. Tansy’s persistence makes it a major concern for land management and ecological health.

Tansy 
Credit: The Spruce

Purple Loosestrife (Lythrum salicaria)

Originally introduced to North America with early 19th-century sailing ships using soil as ballast, purple loosestrife is now widespread across the U.S., except in Hawaii and Alaska. This vibrant violet-flowered plant can unleash up to two million seeds each season, aggressively invading ecosystems and displacing native species.

This diminishes biodiversity, particularly affecting birds by reducing available nesting sites, shelter, and food sources. Its dense root systems overrun wetlands, displacing native flora and degrading habitats.

Since 1992, the U.S. and Canadian governments have been deploying European beetles like Galerucella calmariensis and G. pusilla to combat its rapid spread, showing promise in controlling its growth.

Purple Loosestrife
Credit: Invasive Species Centre

Japanese Anemones

Commonly found in garden centers, Japanese anemones, including Anemone hupehensis and its varieties, are charming plants that bloom with pink or white flowers and bright yellow centers late in the season. They are vital for insects searching for pollen and nectar late in the year.

Yet, their tendency to spread through underground runners can make them a garden nuisance, quickly dominating spaces, especially in loose, sandy soils. If concerned about their invasive nature, consider containing them in pots.

Japanese Anemones
Credit: Gardeners’ World

Bear’s Breeches (Acanthus)

With varieties like Acanthus mollis and ‘Whitewater’, bear’s breeches are imposing plants perfect for the back of a garden border. They feature large, glossy leaves and tall spikes of white flowers enveloped by purple bracts.

They are generally low-maintenance, unless you need to move them. Their deep roots can be challenging to completely remove, often regrowing at the original site.

Bear's Breeches
Credit: The Spruce

Running Bamboos

Known for their rapid growth, running bamboos like Phyllostachys (including black bamboo), Pleioblastus, and Pseudosasa can become garden nightmares if not carefully managed. They spread via long underground rhizomes and can quickly encroach on other plants.

While clump-forming bamboos like Bambusa, Fargesia, and Thamnocalamus are less problematic, running bamboos might require professional intervention to control their spread, making them a risky choice for small or densely planted areas.

Running Bamboos
Credit: Bamboo Garden Nursery

Spanish Bluebells (Hyacinthoides hispanica)

While the charming British bluebell (Hyacinthoides non-scripta) is a beloved garden addition, its Spanish counterpart, the Spanish bluebell (Hyacinthoides hispanica), can be a problematic guest.

This robust variety self-seeds prolifically, making it an overly enthusiastic grower that can overtake your garden. More concerning is its ability to cross-pollinate with native British bluebells. The resulting hybrid can escape from gardens into the wild, potentially overpowering and displacing indigenous varieties.

Digging up their larger bulbs can help control their spread, but it may take several seasons to thoroughly remove them, and you might need to disturb neighboring plants in the process.

Spanish Bluebells (Hyacinthoides hispanica)
Credit: Gardeners’ World

Passion Flower (Passiflora caerulea)

Among the various passion flower species, the blue passion flower (Passiflora caerulea) stands out for its vigor. This beauty can become overly adventurous, extending long runners and sprouting new shoots far from the original planting spot. While enchanting, it needs careful monitoring to keep it in check.

Passion Flower
Credit: Wikipedia

Oxalis

This genus, with its clover-like foliage and charming star-shaped blooms, can be a mixed blessing. While visually appealing, certain species of Oxalis can become intrusive. Originating from South America and southern Africa, only a few types can withstand UK winters, with invasions more prevalent in milder southern regions.

Species like Oxalis corniculata, Oxalis debilis, and Oxalis latifolia are particularly troublesome, spreading through both explosive seed pods and bulbils that can lie dormant underground for years.

Oxalis
Credit: CABI Digital Library

Bachelor’s Buttons (Kerria japonica ‘Pleniflora’)

This delightful, spring-flowering shrub brightens gardens with its double, bright yellow blooms at a time when few other plants are flowering. It thrives in both sun and shade and adapts to various environments. However, its tendency to spread via suckering rhizomes means it requires management to prevent it from taking over more space than intended.

Bachelor's Buttons
Credit: Gardening Know How

Yellow Loosestrife (Lysmachia punctata)

Yellow loosestrife is an appealing perennial featuring tall spikes of vibrant yellow flowers, making it a favorite among pollinators. It’s an excellent choice for quickly filling gaps in the garden, especially in areas with poor soil and shade, where it’s more manageable.

However, in rich, loamy soil and full sunlight, it becomes a vigorous spreader, extending through both seeds and underground runners. To keep it in check, it’s wise to divide large clumps every three years and promptly remove any new suckers that appear.

Yellow Loosestrife
Credit: wikipedia

Houttuynia (Houttuynia cordata)

This low-lying shrub is notable for its dark leaves and simple white flowers that pop against its ‘Chameleon’ cultivar’s variegated green, red, and yellow foliage.

While perfectly suited for moist environments like pond edges or bog gardens, Houttuynia can be invasive. It spreads through runners and seeds, but you can limit its growth by planting it in drier conditions or confining it to a pot.

Houttuynia
Credit: Wikimedia

Snowberry (Symphoricarpos)

Snowberry is a hardy, suckering shrub known for its striking white berries that last from autumn into winter. It thrives in nearly any soil, making it versatile as ground cover, under tree canopies, or even as an informal hedge.

Despite its benefits, snowberry’s tendency to spread via long runners and suckers, which may appear far from the original planting, makes it challenging to manage. These can be tough to remove, particularly from lawns, and it might take years to completely eradicate them.

Snowberry
Credit: Wikipedia

Yellow Toadflax (Linaria vulgaris)

Introduced from the Mediterranean for its medicinal and decorative uses, yellow toadflax is now commonly seen across roadsides, grasslands, and crop fields, particularly in the Southwest.

As noted by the USDA, this striking, tall flower is not just a visual treat but also a formidable invader. Its high adaptability and resilience make it a significant challenge to control as it competes aggressively with native species.

Yellow Toadflax
Credit: Lillooet Regional Invasive Species Society

Garlic Mustard (Alliaria petiolata)

Originally cultivated for its culinary and medicinal qualities, garlic mustard has become a notorious invader across the United States. While its small, delicate white flowers and garlic-scented leaves may seem charming, this plant poses a threat, especially to species like the rare West Virginia white butterfly, as highlighted by the USDA.

By its second year, garlic mustard aggressively spreads its seeds via the wind, overwhelming native plant populations in forest understories. It also alters the soil’s microbiology, inhibiting the growth of indigenous fungi and bacteria, thereby reshaping the local ecosystem.

Garlic Mustard
Credit: Tualatin Soil and Water Conservation District

Nandina (Nandina domestica/Sacred Bamboo)

Nandina, often called sacred bamboo, has spread beyond its ornamental use, propagating through both underground root sprouts and seeds dispersed by animals.

Although it may take years to mature from a seedling, nandina is robust, capable of displacing native flora and altering plant communities. Gardeners should note its berries are toxic to cats and some grazing animals, adding to its problematic nature.

Nandina
Credit: Trees and Shrubs Online

Autumn Olive (Elaeagnus umbellata)

Autumn olive poses a severe risk to native ecosystems by out-competing local plant species for resources. This shrub can produce up to 200,000 seeds annually, aiding its invasion of diverse habitats. Its ability to fix nitrogen in poor soils enhances its invasive potential, making it a formidable opponent to natural plant succession and nutrient cycling.

Autumn Olive
Credit: Wikipedia

Common Periwinkle (Vinca minor)

While the common periwinkle’s lush, purple flowers may look attractive, it’s an ecological bully. It forms thick mats on forest floors, crowding out both herbaceous and woody native plants. When you see large patches of periwinkle, it’s usually a sign that intervention is necessary to protect the indigenous wildlife and plant life.

Common Periwinkle
Credit: North Carolina Extension Gardener Plant toolkit

Princess Tree (Paulownia tomentosa)

Known for its beauty, the princess tree is an aggressive ornamental that thrives in disturbed natural areas like forests, streambanks, and rocky slopes. Remarkably resilient, it can quickly regenerate after events like wildfires.

This tree adapts well to pollution and various soil types, making it a persistent and invasive species, often growing at the expense of local biodiversity.

Princess Tree
Credit: LIISMA

Weeping Lovegrass (Eragrostis curvula)

Weeping lovegrass has dramatically altered the natural fire cycles in desert ecosystems, leading to more frequent and severe wildfires. It’s not the preferred choice for grazing by livestock and wildlife compared to native grasses, which has allowed it to overpower many native plant communities.

This grass establishes itself swiftly, produces a large amount of viable seed in its first growth season, and can expand its territory by up to 175 meters per year.

Weeping Lovegrass
Credit: Feedipedia

Japanese Spirea (Spiraea japonica)

Japanese spirea is quick to colonize disturbed areas, making its way into meadows, forest clearings, and other vulnerable habitats. Once it takes root, it grows quickly, forming thickets that overwhelm and outcompete local flora. The longevity of its seeds in the soil makes it particularly challenging to manage and restore native vegetation effectively.

Japanese Spirea
Credit: Wikipedia

Chaste Tree (Vitex agnus-castus)

The chaste tree, widely available in nurseries across the U.S., is admired for attracting pollinators and its traditional medicinal uses. However, it’s not a favorite among conservationists, especially those focused on riparian and wetland areas.

Birds can easily spread its seeds along waterways, where they germinate and displace native plant species, disrupting local ecosystems.

Chaste Tree
Credit: The Spruce

Common Mullein (Verbascum thapsus)

While I personally appreciate using common mullein in tea for its soothing effects on the lungs, this plant is a formidable invader in pastures, ranch lands, and meadows. Its seeds germinate effortlessly, outcompeting native species.

As mullein matures, its deep taproot makes removal difficult; any remnants of the taproot left in the soil can lead to new growth, compounding control efforts.

Common Mullein
Credit: Wikimedia

Frequently Asked Questions

  • Q: What are the top five most problematic invasive plants?

A: Some plants have gained a notorious reputation for their aggressive spreading tendencies. Among these, Japanese honeysuckle, knotweed, kudzu, privet, and wisteria are particularly troublesome invaders, often found for sale in many garden centers despite their invasive nature.

  • Q: Why are some invasive species considered successful?

A: A species is dubbed “successful” when it dominates a particular ecological area. However, this success often spells trouble, leading to the displacement of native species and degradation of their natural habitats.

  • Q: Which invasive plant is known for its overwhelming success at spreading?

A: Kudzu stands out as a prime example of an overwhelmingly successful invasive plant. This vigorous vine can engulf virtually any structure or vegetation in its path, smothering and ultimately killing them.

  • Q: Which invasive plant is most commonly found in landscaping?

A: English Ivy is widely favored for its aesthetic appeal and low maintenance, making it a popular choice in landscaping across the United States, despite its invasive characteristics.

  • Q: Can invasive species ever provide any benefits?

A: While generally detrimental, certain species like Vitex and Japanese honeysuckle do offer some ecological benefits by supporting the food needs of various pollinators and birds.

  • Q: Which U.S. state struggles the most with invasive species?

A: Florida’s warm climate and rich biodiversity make it the state most plagued by invasive species.

  • Q: Are invasive species ever harmless?

A: Unfortunately, no. Invasive species are known for their negative impacts on ecosystems, altering soil properties and disrupting local water systems, which harms both wildlife and human communities.

  • Q: What makes invasive plants so adept at spreading?

A: These plants often thrive in new environments by outcompeting native vegetation, which is crucial for maintaining the balance needed for local wildlife and human health.

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