Containing the beauty: Understanding and learning to control invasive species used as ornamentals in your garden
Some ornamental species , such as bishop’s goutweed, creeping bellflower and butterbur, are invasive and can quickly overtake a garden, causing ecological damage and posing a threat to native species.
Gardening is a popular hobby enjoyed by many people worldwide, and it is no wonder why. The beauty of a well-tended garden can be breathtaking, with an array of vibrant colors and textures that are a feast for the eyes. However, not all plants that are used as ornamentals are harmless.
The use of invasive species as ornamentals is a controversial topic among gardeners and environmentalists alike. On one hand, these plants can be beautiful and add diversity to a garden’s design. They are often used for their blooms, their foliage or the ability to cover the bare ground. On the other hand, they can become difficult to control once established and, more importantly, their spread can have negative consequences for the environment.
In this new series of blog posts, I will focus on commonly used ornamental plants that can become invasive and potentially harmful to the environment. Let’s start with three plants that are in my garden … they may be present in your own garden! It’s essential to understand their characteristics and potential risks. I will discuss ways to manage their spread and provide alternatives that are not invasive, allowing you to create a beautiful and sustainable garden that is safe for the surrounding ecosystem.
Bishop’s goutweed
Aegopodium podagraria, commonly known as bishop’s goutweed, is a herbaceous perennial plant that belongs to the Apiaceae family. It is native to Europe and Western Asia and has been introduced to North America, where it is considered an invasive species.
The origin of this common name is not entirely clear, but it is believed to be related to the plant’s historical use as a medicinal herb for treating gout and arthritis.
Bishop’s goutweed has a unique and attractive appearance. It grows up to a height of 2 feet and has a spread of up to 3 feet. It has deeply dissected fern-like leaves that are dark green in color and can grow up to 6 inches long. The plant produces small white flowers in umbels that bloom in late spring and early summer. The flowers are followed by small, flattened seeds that are dispersed by the wind.
Aegopodium podagraria ‘Variegata’ is a cultivar of bishop’s goutweed that is prized for its attractive foliage. Its leaves are variegated with cream or white markings along the edges. The variegation can vary in intensity depending on the amount of sunlight the plant receives.
It is mainly used as a groundcover due to its ability to spread quickly and form a dense mat of foliage. It can be particularly useful in shady areas where other groundcovers may struggle to grow.
The plant has a high growth rate and can spread rapidly, outcompeting native species and causing ecological damage.
Should you decide to have this plant in your garden, mechanical barriers can be an effective method for controlling its spread. This can be done by digging a trench around the perimeter of the area where the goutweed is growing and lining it with a physical barrier, such as heavy-duty landscape fabric or a plastic root barrier. The barrier should be at least 18 inches deep and extend above the soil surface by a few inches to prevent the goutweed from spreading over the top.
Hand pulling can be effective for small infestations of bishop’s goutweed, but controlling larger areas will require a significant amount of effort. For the circle of bishop’s goutweed around a maple, I take good care of mowing regularly. Cutting the plant back to the ground in the fall can also help control its growth as pruning mature flower heads.
Creeping bellflower
Creeping bellflower, or Campanula rapunculoides, is a perennial species of Campanulaceae that can be invasive in gardens. It is native to Europe and has been introduced to North America, where it is considered an invasive species in many areas.
Creeping bellflower has tall, upright stems that can grow up to 3 feet tall, with toothed leaves and clusters of purple or white bell-shaped flowers that bloom in mid-summer. The plant spreads rapidly through underground rhizomes and can quickly overtake garden beds and other areas of the landscape.
While creeping bellflower is often grown as an ornamental plant for its attractive flowers, it can become difficult to control once established in a garden.
I have creeping bellflowers that came “as a gift” with plants from a friend. They did not take long to establish themselves under a tree and I let them be with caution. From now on, I am more cautious with such “gifts”! Hand pulling and digging up the rhizomes can be effective methods of control, but it may be necessary to repeat these methods over several seasons to fully eradicate the plant.
If you are considering planting a bellflower in your garden, try choosing instead a non-invasive species and researching the plant’s growth habits and requirements to ensure it is a good fit for your garden.
Butterbur
Petasites, commonly known as butterbur, is a genus of perennial plants in the Asteraceae family. They are native to Europe and Asia, and several species have been introduced to other parts of the world, including North America.
Petasites are often used as ornamental plants in gardens due to their large, attractive foliage and showy flowers. However, some species of Petasites can be invasive and difficult to control once established, particularly in wetland areas.
One of the most commonly grown species is Petasites japonicus ‘Gigantus’, the giant Japanese butterbur, which has very large, heart-shaped leaves.
The plant’s rhizomes can be quite large and are important for propagation. Rhizomes are horizontal, underground stems that grow sideways, producing roots and shoots at intervals along their length. In fact, butterburs are considered invasive in some regions because their rhizomes can quickly spread and take over a space. This species has been reported as invasive in some areas of North America, where it can quickly form dense colonies and outcompete native plant species.
The flower heads of Petasites are typically large, dense clusters of small flowers that are arranged in a dome-like shape. Each individual flower has no petals, but instead has a group of small, feathery structures called florets that are clustered together to form a composite flower head. They typically bloom in early spring before the leaves emerge. Because the flowers are produced before the leaves, the large flower heads are quite striking and can be a welcome sight after a long winter. However, the flowers are not particularly long-lasting, nor fragrant.
To manage the spread of Petasites in your garden, it is important to plant them in containers or in areas where they can be easily contained. Regular pruning, removal of flower heads and pulling of rhizomes can also help to limit their spread. Never throw the rhizomes in the wild. If you decide to remove invasive butterbur from your garden, it is important to dispose of them properly to prevent further spread.
It is crucial to be mindful of the potential risks associated with growing Petasites in your garden. While they can be beautiful and striking plants, particularly useful on damp, shady and slanted terrain, they have the potential to become invasive and harm the local ecosystem. By being aware of their growth habits and taking appropriate measures to manage their spread, you can enjoy their beauty without putting the environment at risk.
There are many more ornamental perennials and groundcovers with an unruly behavior and I will discuss some of them in a future blog post.
In conclusion, it is important for gardeners to avoid planting ornamental perennial plants in your garden if there’s a risk of them to become invasive. Instead, opt for non-invasive alternatives that are well-suited for your region and climate. When choosing plants, do your research to ensure that they are not invasive and will not spread uncontrollably. If you already have them or are tempted to plant them nonetheless, think ahead of ways to control their growth.
In addition, avoid dumping plant waste from your garden in natural areas, as this can contribute to the spread of invasive species. Instead, compost your plant waste or dispose of it in a way that is appropriate for your area.
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[…] to your area, as they will be well-adapted to the local climate and require less maintenance. Avoid invasive perennials, particularly if they are not recommended for your area. For the border illustrated below, I […]