It’s a sunny day in late February and that means I’m looking at seed catalogs and dreaming of new plants! Have you been plant shopping yet this year? Adding new plants and seeds to your garden creates new scents, textures, colors, and shapes and is the easiest way to increase biodiversity in your landscape!
As you begin revitalizing your garden space this spring, I want to bring some attention to invasive plants, a category of plants that should strike fear and dread in your heart! Okay, maybe that’s a bit dramatic, but truly this is a topic that everyone needs to learn more about.
Q. What is an invasive plant?
A. An invasive plant is a non-native, “alien” species that was introduced intentionally or by accident into the landscape and causes ecological and/or economic harm. These plants tend to be free from predators, parasites, and diseases that could help keep them in check. These plants reproduce rapidly with multiple methods (i.e. seeds, stolons, root cuttings, runners, etc.) and spread aggressively. They tend to be deer resistant or deer tolerant, a big reason why they are purchased and planted in landscapes. Below is a photo of purple loosestrife. Notice how it is creating a monoculture, a visual key that might mean the plant is “invasive.”
Did you know that some invasives are still for sale at nurseries, greenhouses, and in mail-order catalogs?
It’s true. Many of the plants on “watch lists” are still readily available to purchase. Japanese barberry is an invasive plant that is a very popular landscape plant still being widely planted today; however, research shows that black legged ticks have been found in areas with invasive barberry thickets because these non-native, invasive forest shrub thickets create ideal microclimates.
Another example of human health concern is that higher numbers of lone star ticks are found in stands of invasive bush honeysuckle.
Q. What’s the big deal with invasive plants?
A. The biggest issue is that invasive plants are better at competing for light, water, and nutrients. In Spring, invasives turn green and break dormancy earlier than native plants, thus giving them a big advantage on growing taller and blocking more sunlight and moisture from the smaller plants. Deer prefer natives and will browse them first. So not only are the invasive plants getting more sun and water, the natives are continually being nipped back by wildlife.
Native insects often do not eat non-native plants and have not had time to develop an ecological dependency on them. Plants are energy producers and the beginning of many food chains. Specific plants are needed for specialist relationships, thus, reduced insect populations result in less available food for organisms further up the food chain. Read more about this concept in this article on biodiversity for the birds from the University of Delaware.
The photo below shows lesser celandine (Ficaria verna), another invasive plant that is aggressive. You can see it is greening up before its surrounding plants— and it appears to be spreading widely on this site. If lesser celandine was not present at this site, there would instead be a mixture of many different plant species in this small area.
Q. How is a plant designated as invasive?
A. Plant categories vary between different agencies, organizations, and states. With regard to legal definitions and restrictions, the Maryland Department of Agriculture (MDA) maintains a list of invasive plants (PDF) that are divided into two tiers, which carry different levels of regulation. The chart below lists Tier 2 invasive plant species in Maryland.
Here is an example of winged burning bush (Euonymus alatus), a Tier 2 invasive plant in the state of Maryland, which means that anytime this plant is sold, it is required to have a warning sign that informs purchasers of its aggressive nature.
Q. Why are invasive plants successful?
A. Invasive plant species produce large quantities of seeds and thrive on disturbed soils. Invasive plant seeds are often distributed by birds, deer, wind, or unknowingly by humans, allowing seeds to move great distances. Some invasives have aggressive root systems that spread long distances from a single plant. See this image of invasive Nandina domestica, sacred bamboo, as an example of a plant that produces large showy fruits containing seeds.
As you begin adding new plants to your landscape, please check out these great resources for non-invasive suggestions:
- Landscaping with Native Plants – Maryland Native Plant Society
- Keystone Plants by Ecoregion – National Wildlife Federation
Resources for invasive plant identification:
- Plant Invaders of the Mid-Atlantic Natural Areas, Field Guide (PDF)
- Do Not Sell! Ornamental invasive plants to avoid with climate change – Northeast Regional Invasive Species & Climate Change Management Network (PDF)
Everyone can help in the fight against invasive plants! Over the next few months, I will be highlighting some common invasive plants. Check out the University of Maryland Extension website on Introduction to Invasive Plants for more information on how to reduce invasive plants. The absolute best way is to just never plant or introduce them into your landscape.