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10 Invasive Ornamental Plants You Should Never Grow

As gardeners, we often seek out beautiful and exotic plants to enhance our landscapes. However, some of these plants can cause significant harm to local ecosystems. Invasive ornamental plants, despite their aesthetic appeal, can outcompete native species, disrupt habitats, and cause long-term ecological damage. It’s crucial to be aware of these problematic plants and opt for safer alternatives that support biodiversity.

In this article, I’ll introduce you to ten invasive ornamental plants that you should avoid growing. Each of these plants is known for its aggressive growth and detrimental impact on local ecosystems. By understanding their origins and the reasons behind their invasiveness, you can make more informed choices for your garden. Let’s dive into the details!

Japanese Knotweed

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Japanese Knotweed (Fallopia japonica) is a highly invasive plant native to East Asia. Initially introduced as an ornamental plant, it quickly spread due to its aggressive growth and ability to thrive in various conditions. Japanese Knotweed can grow up to 10 feet tall and spread through its extensive root system, which can damage foundations, roads, and walls.

One of the most significant issues with Japanese Knotweed is its ability to outcompete native plants for resources such as light, water, and nutrients. It forms dense thickets that can displace native vegetation, reducing biodiversity and altering habitats. Controlling Japanese Knotweed is incredibly challenging and often requires repeated treatments over several years. Avoid planting this invasive species to protect local ecosystems.

English Ivy

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English Ivy (Hedera helix) is a popular ornamental vine native to Europe and Western Asia. While it’s admired for its evergreen foliage and ability to cover walls and ground, it’s also highly invasive. English Ivy can spread rapidly, smothering native plants and trees by blocking sunlight and taking over large areas of the forest floor.

English Ivy’s dense growth can weaken trees, making them more susceptible to disease and damage. Additionally, it can harbor pests and pathogens that threaten native plant species. Removing established English Ivy is labor-intensive and requires persistent management to prevent regrowth. Opt for native ground covers and climbers to avoid the ecological harm caused by English Ivy.

Purple Loosestrife

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Purple Loosestrife (Lythrum salicaria) is an attractive perennial native to Europe, Asia, and Northwest Africa. It was introduced to North America as an ornamental plant but quickly became invasive due to its prolific seed production and ability to thrive in wetlands. Purple Loosestrife forms dense stands that outcompete native plants, disrupting wetland ecosystems and reducing biodiversity.

The dense growth of Purple Loosestrife can alter water flow and nutrient cycling, impacting aquatic habitats and wildlife. It’s challenging to control once established, often requiring mechanical removal, herbicides, and biological control methods. Avoid planting Purple Loosestrife to protect wetland environments and choose native alternatives that provide ecological benefits without the invasive tendencies.

Kudzu

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Kudzu (Pueraria montana) is a fast-growing vine native to East Asia, introduced to the United States for erosion control and as a forage crop. However, its aggressive growth has earned it the nickname “the vine that ate the South.” Kudzu can grow up to a foot per day, smothering trees, shrubs, and structures with its dense foliage.

The rapid spread of Kudzu can outcompete native vegetation, reducing biodiversity and altering habitats. Its extensive root system can also degrade soil quality and increase erosion. Controlling Kudzu is incredibly challenging, often requiring repeated treatments and persistent management. Avoid planting Kudzu and opt for native vines that support local ecosystems without causing harm.

Yellow Flag Iris

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Yellow Flag Iris (Iris pseudacorus) is a striking aquatic plant native to Europe, North Africa, and western Asia. While it’s admired for its bright yellow flowers, it’s also highly invasive in wetland environments. Yellow Flag Iris spreads rapidly through both seeds and rhizomes, forming dense stands that displace native vegetation and alter habitats.

The dense growth of Yellow Flag Iris can impede water flow, increase sedimentation, and impact water quality. It’s also toxic to livestock and wildlife, posing additional risks to local ecosystems. Controlling Yellow Flag Iris requires persistent effort and often involves a combination of mechanical removal and herbicides. Avoid planting this invasive species to protect wetland habitats.

Giant Hogweed

giant hogweed
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Giant Hogweed (Heracleum mantegazzianum) is a large, dramatic plant native to the Caucasus region and Central Asia. It was introduced to Europe and North America as an ornamental plant but has become highly invasive due to its rapid growth and prolific seed production. Giant Hogweed poses a significant health risk, as its sap can cause severe skin burns and blisters when exposed to sunlight.

In addition to its health risks, Giant Hogweed can outcompete native vegetation, reducing biodiversity and altering habitats. Its large size and dense growth can also increase erosion and impact water quality. Controlling Giant Hogweed is challenging and requires careful handling to avoid sap exposure. Avoid planting this dangerous and invasive species to protect both human health and local ecosystems.

Autumn Olive

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Autumn Olive (Elaeagnus umbellata) is a fast-growing shrub native to East Asia. It was introduced to North America for erosion control and wildlife habitat but has become highly invasive due to its ability to fix nitrogen and thrive in poor soils. Autumn Olive forms dense thickets that outcompete native vegetation, reducing biodiversity and altering habitats.

The dense growth of Autumn Olive can change soil composition and nutrient cycling, further impacting native plant communities. Its berries, while attractive to birds, facilitate its spread and exacerbate its invasiveness. Controlling Autumn Olive requires persistent effort, including mechanical removal and herbicides. Avoid planting Autumn Olive and choose native shrubs that support local ecosystems without causing harm.

Tree of Heaven

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Tree of Heaven (Ailanthus altissima) is a fast-growing deciduous tree native to China. It was introduced to North America as an ornamental plant but has become highly invasive due to its rapid growth and prolific seed production. Tree of Heaven releases chemicals into the soil that inhibit the growth of other plants, further reducing competition and allowing it to dominate the landscape.

The aggressive growth of Tree of Heaven can outcompete native vegetation, reduce biodiversity, and alter habitats. Its extensive root system can also damage infrastructure and increase erosion. Controlling Tree of Heaven requires persistent effort, including mechanical removal and herbicides. Avoid planting this invasive tree and opt for native species that support local ecosystems.

Brazilian Pepper

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Brazilian Pepper (Schinus terebinthifolia) is an evergreen shrub or small tree native to South America. It was introduced to North America as an ornamental plant but has become highly invasive in subtropical regions, particularly in Florida. Brazilian Pepper forms dense thickets that outcompete native vegetation, reduce biodiversity, and alter habitats.

The dense growth of Brazilian Pepper can also increase fire risk by creating highly flammable thickets. Additionally, its sap can cause skin irritation in some people, making it a nuisance in residential areas. Controlling Brazilian Pepper requires persistent effort, including mechanical removal and herbicides. Avoid planting this invasive species and choose native alternatives that support local ecosystems.

Chinese Privet

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Chinese Privet (Ligustrum sinense) is a fast-growing evergreen shrub native to China. It was introduced to North America as an ornamental plant but has become highly invasive in many parts of the United States. Chinese Privet forms dense thickets that outcompete native vegetation, reduce biodiversity, and alter habitats.

The dense growth of Chinese Privet can also impact water quality and flow in riparian areas by displacing native vegetation that stabilizes soil and filters water. Controlling this invasive shrub requires persistent effort, including mechanical removal and herbicides. Avoid planting Chinese Privet and choose native shrubs that provide ecological benefits without the invasive tendencies.

Cody Medina
Small Scale Farmer
Hi there! I'm Cody, a staff writer here at The Garden Magazine and a small-scale farmer living in Oregon. I've been gardening most of my life and now live on a quarter-acre farmstead with chickens, ducks, and a big garden.