The Latest on Weeds
Startling insight on why you’ve been removing weeds wrong your whole life
Dear Avant Gardener, I'm curious as to why pulling weeds is "out." I'm a native of southern Wisconsin, but relocated about two years ago to about 30 minutes north of Denver. It's always been a very satisfying gardening experience for me to pull weeds out with the roots – the longer the roots, the better! In this drier climate though, it's harder to pull weeds. Just yesterday, I was pulling some taller clumps of grass in a stone-landscaped area and more often than not, they broke off at the ground. — Dawn, Firestone, CO
Ugh, weeds! I listed pulling weeds as “out” and cutting them as “in” in my spring “In & Out” list based on Larry Weaner’s advice in his seminal book on ecological landscaping, Garden Revolution (2016):
Pulling roots disturbs the soil, and disturbing the soil activates seed germination that typically results in weeds. So when you pull a weed by the roots, you are initiating and perpetuating a never-ending cycle of weeding. Alternatively, cutting the plant creates no soil disturbance and generates far fewer replacement weeds.
But the plant will just come back, right? Yes, it will in a garden where open mulched spaces between the plants allow it to receive light the minute it resprouts. If, however, you cut it below the foliage in a dense, intermingled ground level, there will be little or no light available, and the resprouting weed is not likely to break through into the sunlight. In addition, it has to compete with the extensive root systems of the plants that have not been cut and are continuing to photosynthesize and become stronger. A particularly vigorous weed may break through once, or even twice, but it will not likely survive beyond that. — Garden Revolution
My Rhode Island yard currently illustrates the downside of pulling weeds where the soil is filled with weed seeds. Where last year I pulled out invasive English ivy and oriental bittersweet, the ground is densely covered by equally invasive garlic mustard and ground ivy. And where we planted plugs, their roots are entwined with speedwells and mouse-eared chickweed, which grow in the lawn we removed.
Controlling weeds by cutting (as well as pulling) requires vigilance, persistence and time, as well as competition from beneficial plants.
[Cutting] is most effective with annual and biennial weeds. . . . Consistency is crucial: if you allow the plant to regrow and retain leaves for a significant period between cuttings, this technique will not work. . . . The cons are that this technique may require a prolonged period when applied to perennials. In addition, it may not work on weeds with large capacities to store food in roots or rhizomatous or tap-rooted species, such as mugwort (Artemisia vulgaris). — Garden Revolution
Read on for tricks and tools I’m using to cut and replace my latest crop of weeds. And consider yourself “in” for breaking off those grasses at the roots!
Dear Avant Gardener, Is there any way to control mugwort short of digging up the entire garden or resorting to using Roundup? We lost one hydrangea that was infested and now one beach plum bush is being crowded. — Bill, Dennis, MA
Oh, no! That’s a tough one! As Weaner notes above, mugwort spreads by roots (rhizomatous) and is difficult to control by cutting alone. I’m going to suggest two strategies to try in combination with cutting: trenching and rhizomatous competition.
Trenching for rhizomatous invasives
Encircling the mugwort on your property with a trench and/or root barrier can stop its spread so you can focus on eliminating the existing infestation. Katie Schortmann, garden coordinator/environmental educator at Audubon Society of Rhode Island, tells me such trenching, in combination with goats, has successfully controlled mugwort, which spreads primarily by rhizomes, not seed.
The root system is extensive though shallow (to 20 cm in depth), with numerous branching rhizomes up to 1 cm in diameter. Plants can regenerate from rhizome fragments as small as 2 cm (Klingeman et al. 2004). — New York Invasive Species Information
Having used this method successfully to eliminate invasive bamboo from our yard in Florida, I suggest digging a 10-inch deep trench around the furthest extent of the infestation, lining the near side with a thick, removable weed barrier (affiliate link), then filling it with stone or shells. Our trench runs 100 feet along one side of our property, is lined with tar paper (which I don’t recommend), and is filled with local littleneck shells.
Fight fire with fire: Rhizomatous native plants
Once you’ve contained the mugwort, you can eliminate the infestation by keeping it shorn to the ground and planting rhizomatous natives in its place. If your infestation is big enough (I hope not!), the picturesque option is to rent goats from Goats to Go in Massachusetts. However, it’s probably more practical to replicate the effect of goat grazing by mowing, shearing, or pruning (see “How” below). Mugwort can tolerate mowing for at least two years, so be prepared to maintain vigilance for that long.
Note that providing competition with native plants is key to successful eradication of invasive weeds. In addition to providing shade so weed seeds cannot germinate and weed plants cannot photosynthesize, as Weaner notes, native plants can compete at the root level, too. Nancy Lawson, aka the Humane Gardener, has successfully battled mugwort with other rhizomatous plants:
So I also started planting other things that grew in a similar way, like Jerusalem artichoke, mountain mint [Pycnanthemum], these things that could really take over the ground in the shady part, the golden ragwort, the robin’s plantain [fleabane, Erigeron pulchellus], and these other things that would really either shade out germination of the mugwort seeds or compete directly with the roots. —Nancy Lawson on the Away to Garden podcast
According to Lawson, mountain mint, obedient plant, common milkweed, black raspberry, and pokeweed will also outcompete and replace mugwort.
Fortunately, beach plum is a robust — and fabulous — native shrub, so it should survive if you soon start cutting the mugwort around it.
Wishing you joy in the Zen of cutting!
Dear Avant Gardener, What about dandelions? Pro or con? – Deidre, Millerton, NY
Meh. I don't like dandelions, but I certainly wouldn't use herbicide or worry about having them in my lawn. I’m lackadaisically cutting them in beds where I removed the lawn and planted natives. Once those beds are established in a couple of years, I’ll probably start cutting dandelions out of the lawn, too. I’ll need a constructive outlet for my pruning habit!
Why, How, Wow!
By definition, a weed is any plant growing where it’s not wanted. Four hundred years ago, European colonizers did not consider dandelions and mugwort weeds when they brought them to New England as medicine. They considered weeds the native plants that appeared in their yards among these imports — which is why so many excellent native plants have the word “weed” in their names. Later generations — up to the present — imported ornamentals, too; oriental bittersweet, a vine native to China, Japan and Korea was introduced here as an ornamental around 1860. Unfortunately, some imported species have adaptations like aggressive roots or high seeding rates that allow them to escape cultivation and outcompete native plants, endangering and even eradicating native plant species and the beneficial insects that evolved with them.
In my garden, I consider aggressive non-natives to be weeds and hope to vanquish them over time by replacing them with natives. I’m most concerned about those I observe rapidly spreading. These include popular garden plants like crepe myrtle and rose of Sharon (grrrrr), as well as commonly recognized invasives like garlic mustard and oriental bittersweet. In the spirit of accepting those things I cannot change, I tolerate dandelions and speedwells in my lawn and am learning to appreciate Dutch white clover.
The concept “weed” leaves room for self expression, too. In my moonlight garden, where I want only white flowers, I consider yellow native evening primrose (Oenothera biennis) — one of several native volunteers in my yard — to be a weed. I was relieved to learn it will probably phase out on its own, so no need to cut it out, a reason to research your weeds before taking action.
Common evening primrose does well in newly established landscapes, but does not persist. Seeds stay, however, and germinate if soil is disturbed. – wildflower.org
New methods call for new tools. To control invasive weeds, I use:
1. Identification apps
Weeds appear spontaneously and are often mysteries. The gold standard identification app is iNaturalist, but I don’t have the patience to wait for fellow citizen scientists to verify a species when I’m cutting weeds in a bed. My default app is Picture This, which is fast and kinda accurate; I appreciate the native range map you can find by scrolling down to the bottom of plant info pages. Sadly, much of the other information is drivel — e.g., reporting a species is invasive and then extolling it for being easy-care. Because automatic app identifications are so often wrong and it’s so hard to differentiate seedlings, when in doubt, don’t cut it out.
2. Cutting tools
Depending on the size of the infestation and the number of precious natives intermingled in it, I recommend using — from broad to fine — a cordless electric mower, a cordless electric string trimmer, a cordless electric grass shearer, and needle-nose fruit pruners. (#affiliate links)
I’m absolutely in love with my RYOBI ONE+ 18V Cordless Battery Grass Shear Trimmer. While clipping away with my little pruners, I imagined designing a sort of electric razor for weeding. It later dawned on me that such a tool might exist and I eventually found a variety of cordless “grass shearers.” After some success with another brand, I bought the more powerful Ryobi. I used the grass shear blade to cut to ground level a eight by four foot infestation of garlic mustard in 15 minutes, carefully avoiding native lily-of-the-valley shoots by holding them back like a barber pushing back an ear to cut around it. (Though, unlike barber clippers, this tool could probably cut off your fingers.) Afterward, I used the hedge blade to cut down a patch of multiflora rose nearby. It looks messy, but I left all cut-off leaves where they fell to act as mulch and to foil rabbits.
3. Small rake
Another tool I conjured up that turns out to exist is a narrow rake to remove cut weeds from among young plants. I recommend only doing this with weeds that are large and heavy — so they impede growth underneath them — or have gone to seed. Otherwise, just leave them to compost naturally in place.
A major downside of removing weeds is it makes your young plants more visible to rabbits. After my weeded purple poppy mallow became rabbit food — ouch — I’ve decided to tolerate the mess of speedwells in some beds. Elsewhere, where I can see native violet volunteers pushing up among the same weeds, I’m removing the speedwells to give the violets more sunlight.
4. Weed replacements
As Aristotle said, nature abhors a vacuum. A plant will soon grow anywhere you’ve removed a weed. If you don’t have natives like my violets eagerly waiting to grow into ground where weeds were growing, put something else there — preferably plants. I rushed out to Prickly Ed’s Native Plant Emporium and bought lady ferns and white wood asters to replace the garlic mustard I cut down with my shears. Elsewhere, I lay down cardboard boxes to smother an area of dirt where I removed creeping Charlie while I decide what to plant there. Four-plus inches of mulch would also work; however, because it so stymies spreading, I don’t use thick layers of mulch in perennial beds. My heart breaks when I see so many neighborhood plants languishing in a sea of mulch!
A real success is when you remove weeds and native plants flourish in their place. When the seed bank contains natives, even pulling weeds can succeed. In my Florida yard, for example, native sea oxeye daisy and beggarticks grew where I pulled out invasive wedelia and Bermuda grass. But that yard is surrounded by hundreds of thousands of acres of pristine wilderness.
In densely populated Rhode Island where Europeans have gardened for 400 years, the seed bank is apparently filled with invasives. That’s why I am so happy that native violets filled in after I cut weeds in my front garden bed a couple of weeks ago. Isn’t this divine?
Establishing a meadow? Read about mowing to control weeds in 3 Steps to a Meadow.
Need to protect weeded beds from rabbits? See Keep Your Plants Safe.
Looking for native plants to outcompete your weeds? See Nancy Lawson’s handout, How to Fight Plants with Plants.
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