The combination of sunlight, warm temperatures, higher levels of carbon dioxide in the air, and rain is a recipe for abundant plant growth. Unfortunately for gardeners, this also means rampant growth of undesirable plants or weeds, those pesky plants that seem to pop up everywhere, in between, and in some cases, all over the plants that we want to have growing in our gardens.
Yet weeding can be quite satisfying, the results are immediately apparent, and one feels good about setting things back to “order” in the garden.
As a person who harbors a deep appreciation for all plants, I do marvel at the tenacity, the toughness, the survival strategies of weeds and their will to live. They exist on a spectrum of influence, from nearly harmless to downright ecologically harmful or invasive. Their exuberance in growth isn’t limited to originating from another continent; indeed, some of our beautiful native species have a reputation for being thuggish or aggressive when growing in the wrong context. And just like our cherished garden plants, weeds are annual, biennial, and perennial, some becoming woody, vining, shrubby, or arborescent.
Each plant demands a different tactic when hoping to rein in its growth. But before we delve into what to do, we must discuss whether or not eradication or suppression is the most feasible when dealing with weeds. It is tempting to imagine a weed intervention that results in all of the plants going away and never returning, even more so if that intervention did not involve the use of harsh chemicals and without any collateral damage. I have even been known to dream about a Harry Potter-style magic spell that would lift all the weeds out of the ground at once and make them disappear.
Sadly, no such spell exists, and holding onto the idea that you can get rid of weeds in one fell swoop is a flight of fantasy. Suppression is the best approach, and when combined with competition from desirable plants and timely interventions that leverage our knowledge of weed species, a gardener can hope to keep weeds in check.
To begin, why are weeds so good at survival? It turns out that they love the disturbance that we create as we garden or as we alter the landscape. Many produce prodigious amounts of seeds that can remain viable in the soil for up to a decade. I am thinking of garlic mustard in this case, capable of generating between 600 and 7,500 seeds from a single plant, and each seed is still able to germinate for up to 10 years later.
The cruel irony is that every time you pull up a garlic mustard, you bring more seeds to the surface for next year. Not letting them go to seed is the first step in suppression. Annual and biennial weeds respond well to this strategy, robbing them of their ability to return by reducing their seed production.
Some perennial species produce aggressive rhizomes that spread underground. Perennial and predominantly woody weeds are a completely different beast altogether.
Weeds of the Northeast is an excellent reference guide to learning more about which weeds plague your garden. Mass Audubon and the Massachusetts Association of Conservation Commissions have great online resources, too.
One reader writes about his frustrations with one nasty customer, Asiatic bittersweet, an ecologically harmful perennial vine that originates from Asia.
Q. I think it’s bittersweet — so I hope I’m classifying it correctly — but it’s my latest obsession, though it has been for some time, but the last few weeks it has been particularly top of mind as I spend most weekends landscaping my property.
I tore piles out between my house and a neighbor — it felt good to get it out of there. I ripped a thick, attached vine from a massive tree while feeling good about “saving” the tree. But today, I read that ripping bittersweet out can actually reinforce its regrow, leaving the soil prepared for more invading.
Chemicals seem to be the only thing to really kill them, and with their abilities to regenerate, it’s impossible with a two-gallon spray bottle — and no idea if it’s safe for kids or wildlife. I feel like it’s absolutely everywhere and it has the perseverance to take over vegetation. We live in Chelmsford, but in Haverhill — where my parents live — there’s none in their neighborhood, for now.
I know we call them invasive for a reason, but how did it become so prevalent and can we really get rid of it? The town I last worked for put $45,000 toward invasive species on town-owned land, but that will hardly make a dent.
Patrick, Chelmsford
A. Bittersweet (Celastrus orbiculatus) is one of the worst threats to our fragmented ecosystem and has a long, sordid history of how it became so prevalent in the region. The future holds more challenges, as bittersweet, along with other woody vines such as poison ivy, are responding to higher levels of carbon dioxide in the atmosphere with increased growth and vigor.
Harvard University botanist Peter Del Tredici wrote a fascinating article that traces the journey of Asiatic bittersweet from Japan to the shores of North America. It is a route that many of our worst invasive species followed, introduced to the United States as ornamental plants. Bittersweet debuted in the nursery catalog of Kissena Nurseries in New York City in 1887 and was found growing in 21 states by 1970. Its spread was aided through nursery sales and its promotion for roadside soil stabilization in New Jersey, Rhode Island, and Massachusetts.
The red berries from Asiatic bittersweet attract birds that spread the invasive weed. Garry Kessler
The vine produces copious amounts of red berries, which, when eaten by our avian friends, further aid its dispersal. I learned this firsthand as the area directly underneath my winter bird feeder sprouted thickly this spring with bittersweet seedlings.
With large vines entangled in nearby trees, there is an endless supply of seeds to establish and reestablish the vines. If you plant other fruit-bearing trees and shrubs like viburnums, chokeberry, hollies, and dogwoods, the birds will end up dispersing those plants rather than the bittersweet.
For control and suppression, I recommend physical removal of small-diameter stems (up to 1 inch thick). For larger stems, repeated cutting or targeted painting of the freshly cut stem with herbicide is effective. Be sure to use the herbicide judiciously and carefully. Keep children and pets away for at least 24 hours.
For suppression to be successful in the long term, repeat visits and vigilance are needed. At the municipal level, advocate for more long-term funding to suppress invasive species; short-term injections of funding without follow-up in the subsequent years tend to result in reestablishment.
Ecologically harmful species are an immense challenge, and one can be easily overwhelmed by the scope of it. But do not lose hope! The fight is a noble one and well worth the effort to ensure that future generations enjoy functional ecosystems as well.
Ulrich Lorimer is the director of horticulture at the Native Plant Trust in Framingham. Send your gardening questions, along with your name/initials and hometown, to ulorimer@nativeplanttrust.org for possible publication. Some questions are edited for clarity.