As gardeners, we all know the thrill of wandering through a garden centre, our eyes widening at all the pretty plants that would add color and interest to our landscapes.
However, amidst this plant paradise lie a few silent invaders.
These plants may initially appear harmless, but they possess an invasive nature that can not only wreak havoc on your garden, but also pose a threat to nearby habitats and ecosystems.
From fast-spreading ground covers to aggressive climbers and unruly shrubs, we expose the potential risks they pose and the detrimental effects they can have on native flora and fauna. But don’t worry, we won’t leave you empty-handed. We also offer alternative plant suggestions that are non-invasive, ensuring you make environmentally-friendly choices for your landscape.
A Note on Invasive Plants
Some of the plants listed below may be considered invasive and/or aggressive in one area and not another.
Even if they are not considered invasive by a government agency, many fellow gardeners have an unfavourable experience with these particular plant species.
The term invasive is relative and dependent on your region and geographical climate. State extension services are a great place to start with research on your region’s invasive plants.
Plus, a plant may not be invasive in your area now, but in the future it may just make the list. For example, the ornamental callery pear was widely sold for decades as the ideal landscape tree. But, as of 2023, it is now on the invasive species list in several states because of its ability to dominate young forest areas and inhibit the growth and establishment of native plant species.
Most landscape plants peacefully coexist, but the following 11 plants have a tendency to overpower your garden.
1. Chameleon Plant (Houttuynia cordata)
USDA zones 5-11
The chameleon plant is a fast growing perennial ground cover that spreads vigorously through underground rhizomes that are fragile and break easily. Even when you think you have pulled it all up, it will resprout from the root system.
The foliage is colorful, adding shades of pink, green and yellow throughout the season. But don’t let this plant fool you. Its attractive foliage is not worth the headache. It is very difficult to keep this plant with invasive tendencies within bounds.
If you like the look of its colorful foliage, a good alternative would be anything in the coral bells or foamflower family. They are available in a wide array of colors and form small clumps of foliage that stay compact to provide color and interest to the front of a border. They can also be used as a ground cover.
2. Lily of the Valley (Convallaria majalis)
USDA zones 3-8
With its pretty bell-shaped white flowers and short habit, lily of the valley may look innocent, but it can spread aggressively through underground rhizomes which may negatively affect native plant populations. Plus, all parts of this plant are very poisonous.
This plant is still commonly available in garden centers in some states, while other states list it as an invasive plant because of its tendency to quickly form large colonies.
If your eyes are drawn to the attractive blooms, a few good alternatives would be snowdrops, white bellflower, or white balloon flower. All are low-growing and can provide spring or summer blooms.
3. Butterfly Bush (Buddleia)
USDA zones 5-10
Butterfly bush is a very popular perennial plant that helps attract butterflies and other beneficial pollinators to your garden space. The attractive blooms are available in a wide array of colors that would complement any landscape.
But this plant can self seed and easily invade open spaces and crowd out native plants. The wild species can even invade riverbanks and reforested areas. The Butterfly bush is considered invasive in many states, as well as England and New Zealand. Some states, like Oregon, have even banned sales of the plant.
However, recent breeding is coming to the rescue. Growers have developed seedless and sterile varieties that may also be available at your garden center. Look for the trademarked series called Lo & Behold or Flutterby.
When shopping be sure to do your research and give preference to those varieties that are listed to be sterile or seedless.
4. Callery Pear (Pyrus calleryana)
USDA zones 5-9
The ornamental callery pear, often referred to as bradford, cleveland select or chanticleer, has an invasive side.
When the tree was first placed on the market it was believed to be unable to reproduce by seed. However, as cultivars cross pollinated, viable seeds were produced and the tree spread within local landscapes and other natural areas.
As the trees spread, they crowd out native species which are relied on heavily by local wildlife, butterflies and other pollinators.
It has become so invasive that some states have made it illegal to grow, sell and plant these trees.
A few safer alternatives to replace the callery pear are serviceberry, eastern redbud or flowering dogwood.
5. Running Bamboo (Phyllostachys/Pleioblastus)
USDA zones 4-10 (depending on species)
Bamboo is known for its versatility and quick growth habit, filling out into a nice privacy hedge at a rapid pace.
But once planted, this fast grower can become incredibly invasive with its complex root system that can spread and grow underground, sending out runners up to 100 feet (31 m) away. This means your new bamboo patch may suddenly spread to your neighbor’s landscape, as well as their neighbor and so on. Plus, this extremely vigorous plant is almost impossible to eradicate once it has taken over.
The type of bamboo in question is running bamboo and as noted, it can degrade natural areas and displace native plants.
Clumping bamboo on the other hand grows just as the name suggests: in a clump. And it normally stays where you’ve planted it. This type would be recommended as a well-behaved bamboo in the landscape. It is fairly well-mannered and its root system circles the parent plant, with a steady but slow spread.
If you do plan on adding bamboo to your landscape, do your research and be certain which species you are planting.
If you’re after the look of bamboo but want to keep this invasive plant out of your landscape, try any of the tall and upright ornamental grasses available at the garden center. Or, if a privacy hedge is what you covet, arborvitae, cedars and junipers would all be good choices.
6. Burning Bush (Euonymus alatus)
USDA zones 4-8
Burning bush is an extremely popular ornamental shrub with vibrant red fall color commonly found both in residential landscapes and commercial plantings.
In some areas, it is now considered to be a threat because of its ability to invade natural areas and outcompete native plant species that are used for both food and shelter by local wildlife.
This shrub has become widespread along the East coast and much of the Midwest. Some states, like Massachusetts and New Hampshire, have prohibited the sale of this shrub.
Luckily there are plenty of great alternatives that provide similar color and interest in the landscape Blueberry bushes, Virginia sweetspire and oakleaf hydrangeas showcase bright red fall colour along with attractive flowers and multi-season interest.
Red twig dogwood is another option for both fall foliage color and continued interest through the winter with its bright stems.
7. Barberry (Berberis thunbergii)
USDA zones 4-8
The barberry is another common shrub primarily used for its pretty purple or red foliage that contrasts well in the landscape. Recently this shrub has escaped its original landscape confines and is now considered to be highly invasive in some areas, especially eastern North America. Birds will eat the fruits of this plant and distribute the seed, forming impenetrable thickets which shade out wildflowers and other native plants.
And, to make matters worse, it has been shown to have a role in the spread of Lyme disease. A study found that the larger the number of barberry in an area, the higher the incidence of Lyme disease carrying ticks. So, this aggressive plant can not only affect our environment, but also our health.
There are safer plant alternatives to the barberry with similar red or purple foliage color. These include varieties of weigela or ninebark.
8. Scotch Broom (Cytisus scoparius)
USDA zones 5-8
Scotch Broom, with its cheerful yellow flowers, may catch your eye at the garden center.
Even though it is considered a short-lived plant, it is bad news! Not only can it spread aggressively and choke out native plants, but it emits a toxic chemical in the soil that may prohibit other plants from growing.
Plus, wildlife find the shrub unpleasant and may be driven from a habitat overtaken by this shrub.
It has proved to be less aggressive in the East than in the West where it is listed in several states including California, Washington and Oregon as an invasive weed. A mature plant can produce upwards of 12,000 seeds per year so it’s no wonder this plant is on the list.
Fortunately there are plenty of pretty yellow flowering options for your landscape besides the scotch broom. You could consider the yellow wild indigo also known as baptisia or any of the eye-catching yellow blooming exbury azaleas.
9. English Ivy (Hedera helix)
USDA zones 5-11
Many gardeners use English ivy to cover the walls of a building or sprawl along the ground in a shady area. But this non-native plant is now considered invasive in many states and should be avoided.
Its aggressive growth can smother native vegetation and cause extensive damage to natural areas, walls and structures, as it reproduces quickly by both runners and seeds dispersed by birds. It is very difficult to eradicate so the best course of action is to never plant it in the first place.
There are plenty of other ground covers and vines on the market that would do the same job as English Ivy but in a non-aggressive manner. One such plant that would offer old world vibes would be the climbing hydrangea. It has a woody base and glossy green leaves that showcase the large white lacecap flowers. Plus, it grows slowly and is easy to maintain as it grows.
10. Japanese Honeysuckle (Lonicera japonica)
USDA zones 4-11 (depending on variety)
Our native honeysuckles are climbing vines covered with beautiful, sweetly scented flowers in spring. However, their close cousin the Japanese honeysuckle is an invasive weed that can take over your garden, suppress the growth of native plants, and ultimately damage the environment around it. It is spread to other areas by birds who love to feast on its berries.
Luckily, freezing winter temperatures keep the vines in check in cold, northern climates, but in southern and Midwestern states, managing honeysuckle is a never-ending problem.
It is considered a noxious weed in many New England states, a top invasive plant in both Georgia and Florida, and is now listed as a severe threat in Kentucky, Tennessee and South Carolina. Be cautious with this one even if it is intoxicating you with its sweet fragrance.
11. Mexican Evening Primrose (Oenothera speciosa)
USDA zones 4-9
The Mexican evening primrose may draw you in with its delicate pink flowers, but this plant can quickly get out of hand.
This cousin to the yellow evening primrose has been known to outcompete other plants in a flower bed and even take over grassy lawns. It spreads by both seed and strong runners. Even if the plant is pulled or disturbed in any way, new growth will continue from the root system making it extremely difficult to control.
This plant is not technically considered invasive, but there have been enough complaints against it to make this list.
Dianthus, perennial geranium and creeping phlox would all make terrific low-growing alternatives to this pink flowering ground cover.
We hope this information has shed some light on the potential danger of certain plant species and we hope it helps you to make more informed decisions for your garden space.
