Verbena, with its vibrant and long-lasting blooms, is a popular choice for gardeners seeking to add color and texture to their landscapes. A common question is whether verbena is invasive. Understanding the nature of different verbena types and the definition of invasiveness is key to making informed gardening decisions.
What Does “Invasive” Mean for Plants?
An invasive plant species is defined as one not native to a particular ecosystem, whose introduction causes or is likely to cause environmental, economic, or human health harm. These plants establish quickly, reproduce rapidly, and spread aggressively, outcompeting native flora for resources like sunlight, water, and nutrients. Their success often stems from their ability to thrive in disturbed soils, produce large quantities of seeds, or develop aggressive root systems.
Invasive plants can lead to a decrease in overall plant diversity and degradation of wildlife habitats. They can alter ecosystems, potentially leading to the decline or extinction of native species. Invasive plants can also affect agriculture, reduce recreational opportunities, and degrade water quality.
Verbena’s Diverse Nature and Invasive Tendencies
The genus Verbena encompasses a diverse array of species, exhibiting a wide range of growth habits and invasive potentials. Some species and cultivars are known for aggressive spreading in certain regions, while others are well-behaved in garden settings. The invasiveness of a particular verbena can also depend heavily on the local climate and ecosystem.
One notable species often discussed for its aggressive tendencies is Verbena bonariensis, also known as Tall Verbena or Purpletop Vervain. Native to South America, it is characterized by tall, slender stems and clusters of lavender-purple flowers. While popular, Verbena bonariensis can readily self-seed and has naturalized in disturbed areas across parts of the southeastern United States and California. States like Georgia, California, Oregon, Washington, and Texas have placed it on watch lists due to its potential to escape cultivation and spread into natural areas.
Another species, Verbena officinalis, or common vervain, is native to Europe and has spread globally, often due to its historical medicinal uses. While described as a “weed, agricultural weed or environmental weed” in some contexts, there are no widespread reports of Verbena officinalis being an aggressively invasive species that significantly impacts crops or other plants. In contrast, many hybrid verbenas, often sold as bedding plants, are bred to be less aggressive. Cultivars like those in the ‘Superbena’ series or ‘Meteor Shower’ are known for setting little seed, which limits their invasive potential.
Managing Unwanted Verbena Spread
For gardeners encountering aggressive verbena species, several management strategies can help control their spread. Proactive measures are most effective in preventing extensive naturalization. Regular deadheading, which involves removing spent flower heads, significantly reduces seed production. This practice prevents the plant from self-sowing and minimizes new seedlings in subsequent seasons.
Manual removal is another direct method. Young seedlings are generally easy to pull, especially when the soil is moist. For more established plants, digging them out and ensuring removal of as much of the root system as possible can prevent regrowth. Proper disposal of plant material, particularly seed heads, is important to avoid inadvertently spreading seeds. Avoid adding seed-laden material to compost piles unless the composting process reaches temperatures sufficient to kill seeds.
Choosing Responsible Verbena and Alternatives
When selecting verbena for your garden, research local invasive species lists. Many regional agricultural extension offices or native plant societies often provide information on plants considered problematic in specific areas. Opting for non-invasive or sterile verbena cultivars helps prevent unwanted spread. Some hybrid varieties are specifically bred to produce minimal or no viable seeds, making them safer choices for diverse landscapes.
Considering native verbena species is also an excellent option, as they are adapted to local conditions and support regional ecosystems. Examples include Verbena hastata (American Blue Vervain) and Verbena stricta (Hoary Vervain), both native to North America. These native alternatives provide aesthetic appeal and ecological benefits without posing an invasive risk. For those seeking different plants with similar visual qualities, alternatives like fringed poppy mallow (Callirhoe digitata) offer vibrant blooms and are native in some regions.