Perennials are the backbone of many beautiful gardens, returning year after year with reliable blooms and foliage. Their persistence is part of their charm. However, that quality can sometimes become problematic when particular species grow too enthusiastically, spreading beyond their intended boundaries and overwhelming neighboring plants.
Many gorgeous perennials that gardeners adore for their showstopping flowers or interesting foliage harbor a secret tendency to take over gardens. Some spread through underground rhizomes, others by prolific self-seeding, and some employ both strategies remarkably.
Knowing which beautiful plants might become garden bullies can help you make informed choices before adding them to your landscape.
1. Purple Loosestrife (Lythrum salicaria)
Purple loosestrife creates a stunning display with its tall spikes of vibrant purple-pink flowers that bloom from midsummer to early fall. The plant can reach 3 to 5 feet tall, creating a dramatic vertical element in any garden setting.
Its star-shaped blooms attract numerous pollinators, creating a buzzing symphony of activity during peak flowering time. However, this European native has become one of North America's most notorious invasive plants.
A single plant can produce up to 2.7 million seeds annually, and these tiny seeds disperse easily by wind, water, and wildlife. Purple loosestrife has devastated wetland ecosystems across the continent, displacing native vegetation and reducing wildlife habitat.
Planting or selling purple loosestrife in many states and provinces is now illegal.
Purple Loosestrife Management Strategies
If you already have purple loosestrife in your garden, immediate removal is recommended before it sets seed. Cut flower spikes before they form seeds and dispose of them in sealed plastic bags with household trash. Never compost this plant, as seeds can survive the composting process.
For established patches, digging out the entire root system and removing all fragments is necessary, as even small pieces can regenerate. Some gardeners have succeeded in repeatedly cutting the plants to the ground, eventually exhausting their energy reserves.
For those who love the look of purple loosestrife, consider native alternatives like blazing star (Liatris spicata) or blue vervain (Verbena hastata) that provide similar aesthetic appeal without the invasive tendencies.
2. Lily of the Valley (Convallaria majalis)
Lily of the valley charms gardeners with its dainty, bell-shaped white flowers that emit an intoxicating sweet fragrance in spring. These diminutive beauties stand 6 to 12 inches tall and thrive in shady spots where many other flowers struggle.
Their glossy, bright green leaves create an attractive groundcover even after blooming has finished. Despite its delicate appearance, lily of the valley possesses an iron will to spread. It multiplies through underground rhizomes that form dense colonies and can quickly invade neighboring garden areas.
What starts as a charming cluster can become an overwhelming carpet that chokes out other plants within a few seasons. Additionally, all parts of the plant contain highly toxic cardiac glycosides, which, if ingested, pose risks to children and pets.
Containing Lily of the Valley
The best way to enjoy lily of the valley without battling is containment. Plant it in areas bordered by hardscape elements like sidewalks, building foundations, or garden walls that can physically block spreading rhizomes.
Some gardeners successfully grow it in large containers or areas surrounded by deep edging material extending at least 10 inches into the ground. Persistent removal is necessary for existing patches that have spread too far.
Dig out the plants, meticulously removing all rhizomes, as even small fragments left behind will regenerate. This may require repeated efforts over several seasons.
Consider replacing it with similar but less aggressive shade-loving perennials like European wild ginger (Asarum europaeum) or foam flower (Tiarella cordifolia), which offer attractive foliage without the invasive tendencies.
3. Obedient Plant (Physostegia virginiana)
Obedient plants earned their curious name because their flowers stay positioned when bent to the side. This North American native produces spikes of tubular pink to white flowers in late summer when many other perennials have finished blooming.
Growing 2 to 4 feet tall creates a striking vertical accent in the garden and attracts butterflies, bees, and hummingbirds. Despite being a native plant, the obedient plant behaves anything but obediently in garden settings.
It spreads aggressively through underground rhizomes and can quickly form dense colonies that crowd out neighboring plants. Its vigor often surprises gardeners who plant it for its beneficial qualities and beautiful blooms, only to find themselves battling its spread in subsequent seasons.
Keeping Obedient Plant in Check
New cultivars offer hope for gardeners who love obedient plants but fear their spreading habit. Varieties like 'Miss Manners' and 'Crystal Peak White' are bred to be better behaved, forming clumps rather than running rampantly.
These cultivars provide the same beautiful blooms without the aggressive spreading tendency. If you have the standard species, containing it with barriers is essential. Install deep edging material around plantings, extending at least 8 inches into the soil to block spreading rhizomes.
Another strategy is growing it in areas where structures or large containers naturally limit its spread. Regular division every 2 to 3 years helps control plant size and vigor while providing new plants to share with friends (with appropriate warnings).
4. Yellow Archangel (Lamiastrum galeobdolon)
Yellow archangel captivates gardeners with its variegated silver-splashed foliage that brightens shady areas year-round. Whorls of hooded yellow flowers appear in spring, adding another dimension of interest to this attractive ground cover.
The plant typically grows 12 to 18 inches tall and creates a lush carpet in areas where many plants struggle to thrive. This European native, particularly the cultivar 'Variegatum' (also sold as 'Hermann's Pride'), has become a problematic invasive in many regions.
It spreads both by creeping stems that root at nodes and by self-seeding. Once established, yellow archangels can form dense mats that exclude native vegetation in woodland areas. It's particularly troublesome in the Pacific Northwest and parts of the Northeast, where it has escaped cultivation and invaded natural areas.
Yellow Archangel Containment Methods
Gardeners wishing to grow yellow archangels should maintain vigilant control. Remove flower stalks before seed formation and regularly trim back wandering stems before they can root.
Growing this plant in containers or in areas surrounded by hardscape features can help prevent unwanted spread. For existing infestations, persistent removal is necessary. Pull plants by hand, making sure to remove all rooted stems.
This may need to be repeated several times a year for multiple seasons. As alternatives, consider other shade-tolerant perennials with interesting foliage, such as coral bells (Heuchera species), foam flower (Tiarella cordifolia), or Japanese forest grass (Hakonechloa macra), which provide similar aesthetic benefits without invasive tendencies.
5. Mint (Mentha species)
Mint delights the senses with its refreshing fragrance and bright flavor, making it a popular herb in many gardens. Different varieties offer unique scents and tastes, from spearmint's sweet notes to peppermint's cooling intensity.
The pretty purple or white flower spikes attract numerous beneficial insects, and the plants maintain attractive foliage throughout the growing season. Unfortunately, mint's vigor makes it among the most notoriously invasive garden perennials.
It spreads rapidly through underground rhizomes, sending new shoots far from the original plant. A small clump can become a garden-consuming monster within a growing season. Once established, mint is extremely difficult to eradicate, as even tiny root fragments in the soil can regenerate.
Safe Ways to Grow Mint
The golden rule for growing mint is containment. Plant it in containers, either above ground or buried in the garden with the bottom removed. If planting in a container with drainage holes, place it on a paved surface to prevent roots from escaping through the holes and into the surrounding soil.
Some gardeners dedicate isolated garden areas to mint, surrounded by hardscape borders like sidewalks or driveways. For those already battling a mint invasion, diligent removal is necessary. Dig out plants completely, tracing and removing all rhizomes.
Be prepared for repeated efforts, as missed fragments will quickly regenerate. Cover cleared areas with landscape fabric for a season to smother any regrowth. Consider replacing them with less aggressive herbs like oregano, thyme, or basil that offer aromatic qualities without the invasive tendencies.
6. Gooseneck Loosestrife (Lysimachia clethroides)
Gooseneck loosestrife creates a charming display with unique curved flower spikes that resemble a goose's neck, topped with small star-shaped white flowers. Blooming in midsummer when many spring perennials have finished, it reaches 2 to 3 feet tall and adds architectural interest to garden borders.
The flowers attract pollinators, and the foliage often develops attractive reddish tints in fall. Despite its elegance, this Asian native spreads aggressively through underground rhizomes that can extend several feet from the parent plant in a single season.
Once established, gooseneck loosestrife forms dense colonies that outcompete neighboring plants for resources. Unlike its infamous relative purple loosestrife, it's primarily a problem in cultivated gardens rather than natural ecosystems, but the battles gardeners face with it are no less challenging.
Controlling Gooseneck Loosestrife
For gardeners determined to grow gooseneck loosestrife, strict containment is essential. Plant it in areas surrounded by hardscape elements like sidewalks or garden walls that can act as physical barriers to spreading rhizomes.
Another option is planting in containers or using deep edging material (at least 10 inches deep) to isolate plantings. Persistent removal is necessary if you're dealing with an established patch spread beyond its bounds.
Dig out plants completely, meticulously removing all rhizomes. Fragments left behind will quickly regenerate, so this process may need to be repeated several times over multiple growing seasons.
For a similar visual impact without the spreading tendencies, consider alternatives like blazing star (Liatris species) or white snakeroot (Ageratina altissima) that offer vertical white flowers in summer.
7. Bamboo (Phyllostachys and Fargesia species)
Bamboo creates an exotic, architectural presence in the garden with its distinctive upright stems and elegant foliage that rustles soothingly in the breeze. Different species offer varied heights from dwarf varieties under 3 feet to towering specimens over 20 feet tall.
The evergreen nature of many bamboos provides year-round structure and screening capabilities unmatched by many other plants. There are two main types of bamboo: running (Phyllostachys species) and clumping (Fargesia species).
Running bamboos are the potentially invasive troublemakers, spreading rapidly through underground rhizomes that can extend up to 15 feet annually.
These aggressive spreaders can send new shoots through lawns, under fences, and even through asphalt, creating territorial disputes between neighbors and headaches for homeowners who planted them without understanding their growth habits.
Bamboo Selection and Management
The safest approach for most home gardens is to choose clumping bamboo varieties like Fargesia species that stay in relatively contained clumps rather than running types. These clumping varieties still expand but do so slowly and predictably, making them suitable for ornamental use without extensive containment measures.
Professional-grade rhizome barriers are essential if you're determined to grow running bamboo. These thick HDPE barriers should be installed 30 inches deep with 2 to 3 inches extending above ground level. All seams must be adequately sealed to prevent escape.
Even with barriers, annual inspection and maintenance are necessary to remove any rhizomes attempting to escape over the top. Professional removal is often required for existing running bamboo that's escaped its bounds, as DIY attempts frequently leave rhizome fragments that quickly regenerate.
8. Periwinkle (Vinca minor)
Periwinkle charms gardeners with its glossy evergreen leaves and pretty violet-blue flowers that appear in spring. This low-growing groundcover reaches 4 to 6 inches tall, creating a dense mat that suppresses weeds and thrives in difficult shady areas.
Its ability to grow under trees where grass struggles makes it a popular choice for problem spots in the landscape. Despite these positive qualities, periwinkle can become invasive, particularly in areas adjacent to woodlands or natural areas.
It spreads through trailing stems that root where they touch the ground, forming dense mats that can outcompete native woodland plants. In some regions, particularly parts of the eastern United States, periwinkle has escaped gardens and invaded natural areas, reducing biodiversity by preventing native plant regeneration.
Managing Periwinkle Responsibly
Gardeners wishing to use periwinkle should keep it away from property boundaries adjacent to natural areas and monitor its spread diligently. Regular trimming of wandering stems can help prevent them from escaping cultivated areas.
In smaller garden spaces, physical barriers like hardscape elements or deep edging material can help contain its spread. Persistent removal is necessary to control established patches. Pull or dig out plants, making sure to remove all rooted stems.
Follow up by monitoring for regrowth, as small fragments can regenerate. For alternatives, consider native groundcovers like barren strawberry (Waldsteinia fragarioides), wild ginger (Asarum canadense), or creeping phlox (Phlox stolonifera), which provide similar coverage without invasive tendencies.
9. Dame's Rocket (Hesperis matronalis)
Dame's rocket creates a spectacular spring display with its showy clusters of four-petaled flowers in purple, pink, and white shades. Growing 2 to 3 feet tall adds vertical interest to garden borders and woodland edges.
The sweet fragrance intensifies in the evening, perfuming garden spaces and attracting sphinx moths and other pollinators. Despite its beauty, this European biennial has become invasive across much of North America. Each plant produces thousands of seeds that spread easily by wind, water, and wildlife.
Dame's rocket readily escapes cultivation and invades woodland areas, displacing native spring wildflowers. Its ability to grow in partial shade allows it to thrive in forest understories, forming dense stands that reduce native plant diversity.
Responsible Dame's Rocket Practices
If you already have dame's rocket in your garden, preventing seed production is crucial. Cut flower stalks immediately after blooming, before seed pods form.
Dispose of cut material in sealed plastic bags with household trash, not in compost piles where seeds might survive to spread further. Monitor your garden for seedlings easily identified by their toothy, hairy leaves.
For those seeking similar aesthetic appeal without invasive concerns, consider native alternatives like garden phlox (Phlox paniculata), wild blue phlox (Phlox divaricata), or Virginia bluebells (Mertensia virginica).
These natives provide comparable beauty while supporting local ecosystems. If you particularly love the fragrance of Dame's rocket, sweet rocket (Matthiola longiflora) offers a similar evening scent with less invasive tendencies.
10. Chinese Silver Grass (Miscanthus sinensis)
Chinese silver grass creates a dramatic visual impact with its fountain-like form and feathery plumes that catch the light beautifully, especially when backlit by morning or evening sun.
This ornamental grass grows 4 to 7 feet tall and provides movement, sound, and winter interest in the garden landscape. The arching foliage and silvery seed heads create a distinctive architectural presence unmatched by many other perennials.
This Asian native has escaped cultivation in many parts of North America, particularly in the eastern United States. It spreads primarily through seeds, which are produced in abundance and dispersed widely by wind.
Once established in natural areas, it can form dense stands that outcompete native vegetation and alter ecosystem functions. Its ability to thrive in diverse conditions, from full sun to partial shade and in various soil types, contributes to its invasiveness.
Responsible Ornamental Grass Choices
Gardeners wanting the aesthetic benefits of ornamental grasses without invasive concerns have several options. Many newer cultivars of Miscanthus sinensis, such as 'Morning Light' and 'Strictus', are less likely to self-seed aggressively.
Sterile hybrid cultivars like 'Purpurascens' also offer the same visual appeal without viable seeds. For those seeking native alternatives, consider switchgrass (Panicum virgatum), little bluestem (Schizachyrium scoparium), or prairie dropseed (Sporobolus heterolepis).
These North American natives provide similar architectural qualities and seasonal interests while supporting local ecosystems.
Balancing Beauty and Control
Perennials can bring long-lasting beauty and structure to your landscape, but some can spread more aggressively than expected. These vigorous growers may escape their bounds without proper care and disrupt nearby plantings or local habitats.
By understanding which perennials have invasive tendencies, you can make informed decisions and design a manageable space. Opting for well-behaved alternatives or applying smart containment techniques lets you enjoy their appeal without extra stress.
For inspiration, consider adding a few effortless-looking perennials that offer beauty without the extra work. With mindful planning, your garden can stay lush, balanced, and a joy to maintain.