As soon as European settlers arrived in North America, they began bringing plants from their homelands and introducing new species. Humans have bred, shared, and moved plants from one region of the globe to another since well, since they started growing plants. We do it all the time, so what’s the problem?
Well, maybe there isn’t a problem for some plants. They are well-behaved exotics or introduced plants. They provide more benefits than harm. Tomato sandwich anyone? Like many of our favorite vegetables, tomatoes are an introduced species. Or how about crape myrtles, though there is some disagreement on how to spell these.
Types of Garden Plants
Native plants are species that were here before gardeners started carrying plants into their gardens from other parts of the world. They are indigenous.
The value of exotics can’t be disputed, however, there are some exotic plants that cross the line. They are known as invasive. We aren’t talking about native plants that have aggressive behavior, like spiderwort or bee balm and bergamot. These plants may be a bit too vigorous for some gardens, but there are species of Tradescantia and Monarda that originated in North America. We call these plants aggressive natives. They do have a place in the landscape, just not next to your prized peony or pricy perennial.
So, what’s the big problem with exotic plants that behave badly? These plants escape the garden, moving into natural areas where they outcompete and displace native plants. They may have been valued in the past but now we know they do more harm than good.
Examples include the once recommended Bradford pear, Pyrus calleryana ‘Bradford.’ We now know this tree as an invasive threat that forms thickets, choking out native trees like dogwoods, oaks, and redbuds. The attractively named Princess or Empress tree, Paulownia tomentosa, is another problem. It reproduces prolifically and survives difficult situations including fire. While the flowers may appeal to you, this tree is one of the most difficult to control and is on the top of many invasive lists. Japanese stilt grass, Microstegium vimineum, is another very difficult to eradicate plant that can be seen throughout the area. It covers the floor of natural forests, producing tons of seeds that can remain viable for years.
There are many invasive plants. You may be dealing with them in your own landscape or wondering what you can do to help with the situation. We want to be smarter gardeners and not plant anything today that will become tomorrow’s problem.
The value of plants is subjective. Every gardener will have their own perspective. If you want to attract pollinators like butterflies and bees, visit gardens like Chatham Mill’s Pollinator Paradise for inspiration. Debbie Roos, the creator and curator, is an award-winning Chatham County extension agent. The Pollinator Paradise Garden in Pittsboro, North Carolina, contains 215 species of plants, 85 percent being native to North Carolina. Visit Carolina Pollinator Garden for Debbie’s plant lists and inspiring photos.
If you are creating a formal rose garden, you want to avoid any plants that are known to be problems, thuggish aggressive plants, or harmful invasive plants. If you are interested in creating a sanctuary for yourself and wildlife, it makes sense to focus on native species that are known to provide benefits to native fauna.
So how do you know if a plant is native, exotic, aggressive, or invasive? There are websites that can provide good information. The U.S. Department of Agriculture has an online database of plants. Visit their website and search for plants that are native to the lower 48 states. You can also find non-native plants, indicated by the letter I for introduced. The USDA website lets you search by common and scientific plant name and contains the entire classification from kingdom Plantae and the higher orders, through family, genus, and species. It’s a great tool, but if you are looking for a website that is more specific to North Carolina, visit projects.ncsu.edu/goingnative/howto/mapping/invexse/index.html.
So now you’ve looked up your shrubs and realize your privet (Ligustrum) that blooms in May is an invasive species. What are you going to do? That’s up to you. What do you value more? The shrub or the possibility that it’s producing seeds that are escaping your property and getting into the natural habitat.
It’s not an easy decision when you are appraising existing plants that provide value to you, but when you decide it’s time to add or replace plants you can make an informed decision.
Karen Guy volunteers as a Wake County Extension Master Gardener. She completed the certificate program in general horticulture at NCSU. She is a certified rain garden designer and an instructor for Landscape Maintenance (HOR-3307E3) at Wake Tech. Follow her on Instagram @wakeforestgardener.