Athletes and coaches study game tapes of their opponents, looking for weaknesses and other clues on how to get the upper hand. That’s how gardeners should look at weeds, learning as much as they can about the plants and all their moves.
The process starts with learning the names, because without knowing who’s who, we can get distracted: Dame’s rocket is beautiful, masquerading as lavender-and-white roadside drifts of tall phlox in late spring. But Hesperis matronalis is not native Phlox paniculata — in fact, it has displaced many native plants on its romp across much of the country since its introduction from Europe several centuries ago.
Another trickster is mugwort (Artemisia vulgaris, from Europe and Asia), which can look like some chrysanthemum you once planted — although it isn’t.
Another reason to address weeds by their proper names: Not all plants with the suffix “weed” in their common names are alien invaders. Jewelweed (Impatiens capensis) is a native that supports bumblebees and hummingbirds, among other beneficial creatures. Clearweed (Pilea pumila) is a host plant for various butterflies.
And in a garden setting, even natives aren’t always desirable. I am thinking of you, mat-forming little spotted spurge, Euphorbia maculata, scourge of gravel driveways and patio crevices.
The First Steps
Start by identifying what you’re dealing with, using the help of printed and online field guides (see the suggested resources below). Next, look up the weed’s life cycle.
If it’s an annual (like Galinsoga ciliata, or even crab grass), you don’t want it to flower and set seed, so pull it or mow before that happens. Mulch any bare spots left behind, if they’re not ready to be replanted, to help keep the next generation from sprouting. (Weed seeds love a void.)
Is your target a biennial, like garlic mustard (Alliaria petiolata), or a perennial, like mugwort? Here’s where it pays to study what makes a weed successful.
To understand why garlic mustard is so hard to control, consider its multiple tactics of weedy prowess. A large plant can disperse 7,900 seeds that have an extended dormancy and can lurk in soil for as long as 10 years.
But there’s worse news: Garlic mustard is allelopathic, meaning it contaminates the surrounding soil, rendering it inhospitable to the germination of seedlings even as seemingly sturdy as native red maples. Nothing grows where it has marked its turf.
Knowing that makes me more determined — and also helps me forgive myself for not being able to quickly seize the upper hand.
Look to the Roots
What is the plant’s root system like? Does it have surface runners, called stolons (like the lawn-loving creeping Charlie or ground ivy, Glechoma hederacea)? The most loathed perennial weeds are often those that multiply by rhizomes — underground stem tissue laden with buds ready to sprout anew should any be left behind.
No amount of pulling or digging seems to get to the bottom of perennial field bindweed (wild morning glory, Convolvulus arvensis), which is said to have roots that go down 20 feet. Its sound-alike, hedge bindweed (Calystegia sepium), is a bigger plant, but oddly doesn’t send its roots down so deep — instead, they go sideways as far as 10 feet.
It’s important to know that you can’t just pull on rhizomatous weeds like these, which leaves their power hidden underground. When the soil is moist, loosen it with a fork or spade and patiently follow the trail. Let the area re-sprout, then do it again and again — or cover the spot with plastic sheeting to solarize some of the remains after the first try.
I’m also interested in which botanical family a weed belongs to, because that could provide additional incentive for eradication.
“A lot of weeds tend to harbor various fungal pathogens or viral diseases, or they attract insect hosts,” said Richard Dickinson, an author of the 2014 book “Weeds of North America.”
Dame’s rocket, in the mustard family (Brassicaceae), can transmit mosaic viruses to cauliflower, radishes and turnips. Queen Anne’s lace is closely related to the common garden carrot and can transfer insects and diseases to your carrots. Common chickweed can transmit viral diseases that damage beets, cucumbers, peas, tomatoes and turnips.
Just Keep Weeding
That’s the secret, really. The most expert organic gardeners — those of us who eschew the use of chemicals — have no tricks to make weeds disappear.
Vigilance is key, starting with the ability to recognize the earliest signs of infestation, including what the weed looks like as a seedling, and then acting quickly and repeatedly. Yes, we use mulch, perhaps with a layer of newsprint or cardboard beneath that might slow some opponents. But most of all, we weed.
That works with many weeds, but not the worst. Once I know I am fighting a tough one, I research one final point online: What the Cooperative Extension office nearest to where I garden recommends as the timing and method of treatment, which can differ by region.
And I try to think of weeding — making an observant, slow pass through each bed in the garden, every week, all season — as a meditation, a practice that is part of my life as a gardener. Bending, pulling; bending, pulling.
Sometimes, though, I admit I can’t help thinking of it as all-out war. On those days, I madly stuff garbage bags with seed-laden weeds I have exhumed or ones with rhizomes that could sprout, tying them closed and setting them in the sun next to my compost heap, to cook them to death for weeks before I add the remains (by then harmless) to the heap.
Name That Weed: A Crash Course
The simplest way to identify a weed is probably crowdsourcing. Register for a free account at iNaturalist (using the app or website) and upload a photo with the date and location.
Or do some homework: The Weed Science Society of America’s master list of weed databases is mostly geared toward agricultural and lawn pests. The tools on the site are not prescriptive, but rather for identification purposes, and they have a regional orientation according to which state university created them, but many weeds are widespread.
An old-style, region-specific weed field guide is another trusted tool: “Weeds of the Northeast” by Richard H. Uva, Joseph C. Neal and Joseph M. DiTomaso is the classic for my region. (In field guides, northeast means south to Virginia, north to Maine and southern Canada, and west to Wisconsin, or thereabouts.) I also use Richard Dickinson and France Royer’s “Weeds of North America,” which makes identification easier with detailed plant portraits and photos of weeds at every life stage.
Want to know which weeds are the worst of the worst? The ones that have made their names onto the states’ most-noxious-weeds lists are here, if you’re curious.