5 Surprising Invasive Garden Plants – A Gardener's Warning and Alternatives
Understanding Invasive Plants and Their Impact on Gardens
As a professional gardener, I’ve had the privilege of working in various environments, from high-maintenance London courtyards to expansive estate gardens in Tuscany. Over the years, I've learned that plants can behave in unexpected ways, especially when they are not suited for their environment. Some of the most popular garden perennials and shrubs, often found in nurseries or local plant stores, can become remarkably aggressive, particularly in the wrong setting.
These plants don’t just grow vigorously; they can smother native species, take over woodlands, and even spread many miles from where they were originally planted. In some cases, they become so persistent that professional help is required to remove them. Worse still, they can escape your yard and spread to neighboring areas, which may not be welcomed by your neighbors.
Plant performance varies depending on the region and climate. What might thrive in one area could become problematic in another. Here are five popular plants that have shown invasive tendencies in my experience as a horticulturist, along with alternatives that are more manageable and environmentally friendly.
1. Lily of the Valley
Lily of the valley is a beautiful ground cover plant with an enchanting floral scent. However, once it becomes established, it can spread aggressively, becoming an invasive bulb in certain conditions. This woodland plant thrives under trees and shrubs, making it a problem in wet, shady, and mild settings, particularly in zones 4 through 8.
In places like Maine, lily of the valley has become a serious issue, pushing out native plants. Its persistent root system makes removal difficult. If you’re concerned about its spread, consider the pink-flowering variety, Convallaria majalis var. rosea, which is just as pretty but less aggressive.
It's also important to note that lily of the valley is poisonous, so if you have young children or pets, it’s best to avoid this plant altogether.
2. Daylily
Common daylilies, or Hemerocallis fulva, are known for their long flowering period and vibrant orange blooms. While they may seem appealing, they are considered invasive in several U.S. states, including Virginia and Michigan. Once established, they are nearly impossible to remove due to their thick, fleshy roots.
Daylilies can quickly escape backyard settings and spread along roadsides and in moist woods, forming dense mats that choke out native plants. Instead of growing daylilies, consider planting milkweed, a native species that supports monarch butterflies and provides striking orange blooms.
Live orange butterfly milkweed plants (Asclepias tuberosa) can be ordered online and are suitable for sun or part shade conditions across a wide range of hardiness zones.
3. Rhododendron
Rhododendron ponticum is a popular flowering shrub, known for its purple blooms. However, this species can become a menace in damp, mild conditions, such as those found in parts of the Pacific Northwest. It spreads rapidly, creating dense foliage that blocks light and prevents other plants from growing underneath.
If you enjoy rhododendrons, consider native varieties like Rhododendron macrophyllum or Rhododendron 'Roseum Elegans', which are more ecologically friendly and less invasive.
4. Lantana
Lantana camara is a favorite among gardeners for its colorful blooms, which come in shades of pink, purple, yellow, and orange. However, it is considered thuggish across North America, including Hawaii and California. While it can be grown in pots or deadheaded to limit its spread, it’s best to opt for less vigorous alternatives.
Bee balm (Monarda) is an excellent choice, offering vibrant flowers that attract hummingbirds and bees. Live bee balm plants can be purchased and grown in a wide range of zones.
5. Nandina
Nandina domestica, or sacred bamboo, is easy to grow and popular in many gardens. However, in warmer regions of the U.S., it can become invasive, spreading quickly and crowding out native plants. If you're looking for a shrub with winter berries, consider the native American beautyberry (Callicarpa americana), which produces striking purple berries during the colder months.
Additional Tips for Managing Invasive Plants
Mint is another plant that can quickly establish itself and spread uncontrollably. To manage it effectively, grow unique mint varieties in pots, where their growth can be easily controlled. Pineapple mint, for example, is a great option that adds a tropical twist to summer drinks and meals.
For gardeners looking to enhance their space, there are a variety of accessories available. Floral Garden Gloves provide protection while weeding and pruning, while live plants like butterfly milkweed and bee balm add color and support pollinators.
By choosing the right plants and managing their growth carefully, gardeners can create beautiful, sustainable spaces that benefit both people and the environment.