Submitted by Terry Twigg, Haddam Garden Club.
(June 1, 2021) As rookie gardeners, we all made rookie mistakes—planting too close together; trying to get sun-loving plants to thrive in shade; over- or under- watering or fertilizing or deadheading. We learned, and don’t repeat those mistakes. But even experienced gardeners get tripped up in one area: Garden thugs.
A thug is a plant which, once admitted to your garden, attempts world domination. It’s not necessarily recognized as a true invasive—at least, not yet—but in the minds of many, it should be. (For a list of invasives, see https://cipwg.uconn.edu/invasive_plant_list) Plants, remember, multiply by several methods. The best-known is seeds, but plants may also send out stolons or rhizomes, which are creeping (in some cases, racing) horizontal stems. Stolons grow above ground, and when a node on the stem touches the ground, it sends down roots. Wild raspberries are a good example. They’re definitely thugs, but at least you can see where they’re headed. But rhizomatous plants are the real sneaky ones. They send out grasping fingers underground in every direction, sending up new growth five, ten, twenty feet away. They dive under barriers and around obstacles, and by the time you discover their newest outpost, it’s already so firmly rooted that you’ll break your back before you dislodge it. They have a fallback strategy, too: every broken bit left behind will resprout. Seedlings can be pulled up fairly easily while they’re still small, and stolons, however tenacious, at least can be traced to their ends, but rhizomatous thugs are the champions.
How do thugs get into your garden? Regrettably, they’re often gifts from one gardener to another (“Here, take a piece of this—I have lots.”). And beware: thugs often lurk at garden club plant sales. But all of them are also sold at garden centers, without warning labels, except for the understated “Vigorous” or ”Spreads easily”). To be fair, thuggery can be a function of location and purpose: Both yarrow and Missouri primrose devoured my garden beds, crowding out everything else I tried to grow, yet they’re perfect choices for colonizing a hillside that’s too steep to mow. And some plants that perform as thugs in the rich cultivated soil of a border are reasonably well-behaved in the leaner, wilder areas of your yard.
A few nemeses on my “Never Again” list:
Mint, of course. Even newish gardeners know mint’s reputation. You can try to keep it in bounds by planting it in a pot and sinking the whole thing into the ground—but it will go over the top AND send roots out the bottom. Most members of the mint family (including many herbs) share its traits. Plant them in a pot, yes, and keep that pot off the ground.
Chinese lanterns. These tiny orange balloons are so cute! Until they take over every inch of cultivate soil. Pots, only.
Lily of the valley. This fragrant beauty, so prized by florists and brides, stakes out its territory with determination, and is relentless. It’s also a Level One poison. My niece, hiking the Appalachian Trail this spring, tells how another hiker had to be carried off the trail and rushed to the ER after mistaking the leaves for edible ramps.
English ivy. Also toxic, though less so. English ivy is well-behaved in its native habitat, but in North America it will smother other plants out of existence, kill full-sized trees, and dismantle your house. I am engaged in a battle to the death for the survival of my north foundation.
Chinese wisteria. Beautiful monster grows fast, sends out runners for what seems like miles around, and self-seeds prolifically. Plant our native wisteria instead—just as lovely, and it belongs here.
Loosestrife. This can be the sweet white gooseneck variety, the common yellow, the ground cover “creeping jenny,” or the lovely purple loosestrife that’s killing our marshes. All are aggressive (in fact, all are on the invasive plant list) even though some are still sold by nurseries. Avoid them.
Houttuynia (Chameleon plant). According to the Global Invasive Species Database, this groundcover can spread thirty feet. Enough said. But, while we’re on the topic of groundcovers, note that vinca, ajuga (bugleweed), and Japanese pachysandra regularly escape cultivation and spread to formerly wild places—and they do so at the expense of our native plants. I inherited all three, but if you’re fortunate enough to be able to choose your own, consider natives like bearberry, wild ginger, white wood aster, and partridgeberry.
Sweet autumn clematis and Japanese honeysuckle. Both are lovely vines, and both are characterized by rampant growth and self-seeding. Don’t be tempted. Stick to native honeysuckle and the more restrained clematis varieties.
This is, unfortunately, only a very abbreviated list. Luckily for us, it’s never been easier to research plant characteristics before buying. Just type in the name of the plant and “aggressive” or “invasive” to save your money, your garden, and your back.
All photos from the public domain.