When my family moved into a new home in the spring of 2005, the only plants growing in the garden were a rhododendron by the front door and a few scattered daffodils and ferns. I was delighted to see a stunning perennial pop up a month later.
Being little more than a fledgling gardener then, I didn’t know what the plant was, and to be honest, it didn’t matter: I was in love with my new purple beauty.
Two years later, after graduating from Cornell University’s master gardener program and working as a gardening columnist for my local paper, I sadly knew better: My favourite plant, purple loosestrife (Lythrum salicaria), was considered invasive in my home state of New York.
“But it’s not spreading on my property,” I whined to no one in particular. “It’s actually well-behaved.”
Further research revealed that, although some plants make their invasive nature known at home (looking at you, mint), others are wolves in sheeps’ clothing. They seem well-contained in the garden but become downright thugs when their seeds are eaten by birds and dispersed elsewhere.
Those seeds grow into plants that outcompete native vegetation because they aren’t recognised as food by much of the local wildlife, which would otherwise keep them under control. Unchecked, they grow larger and eventually choke out native plants that provide food, nesting material and shelter for birds, pollinators and small animals. This disrupts the entire ecosystem.
Many state environmental agencies prohibit the sale and use of plants deemed harmful to human or ecological health. But some invasives are not officially designated, and others may be listed by one state but not another. To complicate matters further, some invasives continue to be sold at the retail level.
So what’s a gardener to do?
For starters, avoid any plant advertised as “vigorous,” “fast-spreading,” “quick-climbing” or a “rapid self-sower,” which are marketers’ code words for invasive. Next, familiarise yourself with your home country's list of locally invasive plants.
Yes, I yanked out that purple loosestrife, which the EPA warns “clogs rivers and lakes, grows into mats so thick that boats and swimmers can’t get through and destroys food and habitat for our fish and water birds.”
I replaced it with the tame but equally beautiful Liatris spicata, which has been a respectful resident of my garden for the past 15 years.
Here are seven other garden bullies and suggestions for mild-mannered alternatives
7. INVASIVE: Butterfly bush (Buddleia davidii)
This sounds like a butterfly-friendly plant, but don’t let the name fool you. Although your butterfly bush may, indeed, be covered in butterflies, the food source it provides them is less than ideal. In addition, it forms large thickets that displace native species in the wild.
California lilac (Ceanothus) is an evergreen shrub with deep blue flowers that grows well in zones 8-10, or try the white-blossomed wild hydrangea (Hydrangea arborescens) in zones 3-9.
6. INVASIVE: Scotch broom (Cytisus scoparius)
This is a nitrogen-fixing legume, is easily established even in the worst growing conditions, and its seeds can remain viable in the soil for decades. According to the EPA, it has “invaded most of the remaining Garry oak savannah ecosystems in Oregon, Washington, and British Columbia (and) is considered to be a threat to the native plant community.”
For similar loose-looking shrubs with small yellow flowers, consider Mormon tea (Ephedra) in zones 3-6 or California flannel bush (Fremontodendron californicum) in zones 8-10.
5. INVASIVE: Rugosa rose (Rosa rugosa)
This is ubiquitous on beach dunes along the entire Northeast coast, as well as in coastal areas of the Pacific Northwest and parts of Minnesota, Wisconsin, Michigan, Alaska and elsewhere. It is considered noxious for its ability to displace desirable vegetation.
Arkansas rose (Rosa arkansana), California wild rose (Rosa californica), Carolina rose (Rosa carolina), Rosa virginiana (Virginia rose), Rosa woodsii (Western wild rose) and prairie rose (Rosa setigera) are suitable stand-ins. Choose the native rose named for the region nearest you.
4. INVASIVE: Both Chinese wisteria (Wisteria floribunda) and Japanese wisteria (Wisteria sinensisuse)
These are aggressive vining plants that threaten native species, including large trees.
Seek out the fragrant, stunning American wisteria (Wisteria frutescens) in zones 5-9.
3. INVASIVE: Japanese barberry (Berberis thunbergii)
This forms large thickets and serves as a habitat for deer ticks and black-legged ticks, which transmit Lyme disease and other illnesses.
For eye-catching berries that provide winter interest, consider American beautyberry (Callicarpa americana) in zones 6-10, winterberry holly (Ilex verticillata) in zones 3-9, or red barberry (Mahonia haematocarpa) in zones 5-9.
2. INVASIVE: Winged burning bush (Euonymus alatus)
This produces an abundance of seeds that root easily around the garden and in the wild when dispersed by birds.
For similarly dramatic red fall foliage in zones 3-8, plant “Autumn Magic” black chokeberry (Aronia melanocarpa “Autumn Magic”) or the fruit-producing Northern high bush blueberry (Vaccinium sp.). In zones 2-8, fragrant sumac (Rhus aromatica) is a lovely substitute.
1. INVASIVE: The ornamental Miscanthus grass (Miscanthus sinensis).
Although still widely sold and planted, this has been deemed invasive in more than two dozen states, where it is known to overtake forests, roadsides, fields and other areas.
Plant little bluestem (Schizachyrium scoparium) in full sun or prairie dropseed (Sporobolus heterolepis) in full sun to part shade.
Both are suitable for zones 3-9.