By JIMMY ROGERS
As I’ve visited home gardens of friends and clients, I sometimes cause a bit of confusion referring to one of their plants as invasive. “Oh, it doesn’t spread that fast,” “It’s never been a problem for me,” or even a shrug, are common responses. Sometimes these plants are prized bushes or vast ground covers.
Ecologists tell us that invasive species cause habitat loss and the extinction of native species. So how did they become a centerpiece of many home gardens, and how did our language about them become so muddled?
As long as people have been crossing the oceans to this continent, they have brought their plants with them. Some of those plants were able to survive here, and a very small percentage, perhaps less than 1%, spread into our wild spaces. If we assume that all ecological niches were full before Europeans arrived, then that means any new arrivals displaced existing species, causing them to either decline or disappear from the area.
It’s easy to find wild spaces near Laurel that have been invaded by nonnative plants. A few weeks ago, I took a hike in Rocky Gorge near Browns Bridge Road. It’s one of my favorite spots to see interesting native plants in the wild. I was surprised to come upon a profusion of native spring ephemerals, such as spring beauty (Claytonia virginica), trout lily (Erythronium americanum) and rue anemone (Thalictrum thalictroides) carpeting the forest floor. However, the trail was choked with invasive vines like vinca (Vinca minor), multiflora rose (Rosa multiflora) and Japanese honeysuckle (Lonicera japonica). Many patches which should have been brimming with rare flowers were instead a mat of thick foliage. Unless WSSC, which owns the land, takes greater steps to manage invasive plants, the ephemerals will likely decrease in numbers each year.
It might seem improbable that our home gardens could have much impact on the local woods. Many popular ornamental plants, even those classified by scientists as invasive, seem to stay in one place and do not create copies throughout our gardens. The fact is, nearly every invasive species you find along Rocky Gorge was first planted in someone’s garden because it seemed beautiful and exotic. Birds and other animals can carry the berries of invasive English ivy (Hedera helix) and porcelainberry (Ampelopsis glandulosa) long distances. And many plants, such as invasive butterfly bush (Buddleja davidii) spread their seed for miles on the wind.
We might think our local nurseries could help us avoid invasive species. Unfortunately, most nursery workers have little training in how plants impact the local ecology, and most of the nurseries near Laurel stock and sell invasive plants because of their popularity. Sometimes plants like butterfly bush will have a special section with promotional signage. Other times, an invasive plant like creeping Jenny (Lysimachia nummularia) will be part of a planted arrangement, spilling down the sides of an attractive pot. Rocky Gorge has a sandy floodplain blanketed with creeping Jenny.
So what can the responsible gardener do? First, start with what you have in your garden today. Identify everything — you can use an app such as PlantNet or iNaturalist to help you identify plants by their leaves and flowers. It’s also handy to have a digital copy of Plant Invaders of Mid Atlantic Natural Areas (tinyurl.com/3z5y2r2k) on your phone or laptop; the book has excellent pictures and clear information about invasive species.
If your home has plants from the original landscaping, especially plantings done between the 1960s and ‘80s, there is a good chance that you have invasive Asian shrubs. Look out for barberry (Berberis thunbergii), burning bush (Euonymus alatus) and nandina (Nandina domestica), all of which regularly escape into our surrounding woods. Barberry can harbor ticks as well.
Next, make a plan to remove any invasive plants you find. For some plants, this may only require a few steps, like removing English ivy from a tree to prevent vine coverage, bark damage and resulting disease. For others, like a woody wisteria (Asian Wisteria species) vine along your entire fence, it may take many phases, or even professional help, to remove it all permanently. Prioritize the most problematic plants first as well as those that you can address most quickly.
Whenever you remove invasive plant material, be sure to put it in the trash rather than in the compost or yard waste bin. Many invasive species have seeds that can survive municipal processing, and you could spread them unintentionally.
Also, be aware that while most native gardeners try to avoid using herbicides, sometimes there are no other viable methods to control invasive species. Limited use of an herbicide and following best practices for land management can have a net positive effect on a property that would otherwise have little plant diversity or habitat due to the presence of an invasive species.
Lastly, research new plant acquisitions to make sure they’re not invasive. Pro tip: if you only buy plants native to Maryland, you’ll never buy an invasive plant again.
