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Using Glyphosate

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Ralph Waldo Emerson claimed weeds were plants for which we have not found a use in the garden. I see it differently. To me, weeds are plants that have found a use for my garden. Or should I say a misuse.

Don’t get me wrong, I’m the first to enjoy a bite of sheep sorrel (Rumex acetosella) and I allow the occasionally weedy yet charming Venus’s looking glass (Triodanis perfoliata) to survive. But in the same way that mutts have greater smarts and strength than many highly bred dogs, sturdy weeds can outcompete our flashy, finicky cultivars. This might explain why the time required for weeding is the most common and fervent complaint I hear among gardeners. Especially gardeners who can’t invest hours in hand weeding because of jobs and families or lack of paid help.

I garden in USDA Zone 7, North Carolina. Because the growing season is long, hot, humid and wet, weeds literally own this part of the world. Even in winter, annual weeds can flush and thrive. Here are the weeds that regularly want to misuse my garden: Japanese honeysuckle, Chinese wisteria, kudzu, porcelain vine, Virginia creeper, English ivy, poison ivy, bamboo (not the edible or architecturally useful kind), elaeagnus, Japanese privet, Chinese privet, Ligustrum lucidum, groundsel, Bermuda grass, crabgrass, common sorrel, annual bluegrass, broom sedge, nut sedge, henbit, chickweed, purslane, prostrate spurge and numerous little tree sprouts. (Note that some of these are natives, happy to curtail the diversity of my garden.) Even when I eliminate many of these species on my property, they return by seed borne by wind or birds, or they creep in from my neighbors’ yards.

I was an organic farmer in the ’80s and I use organic gardening techniques and materials on my home gardens, my small nursery and for clients’ gardens. But in our climate, the weeds just keep-a-
comin’, like zombies in a movie. So I’ve adopted careful use of the safest herbicide I could find to rout the weeds: glyphosate. By applying it monthly, I’m able to actually reduce the total amount of herbicide necessary. If you’re already using the organic weed-prevention techniques I describe in “Organic Weed Prevention” and can’t afford the hours that it takes to hand-pull the remainders, you may want to follow my lead.

The truth about glyphosate

Glyphosate (best recognized by the trade name Roundup) is a herbicide with a lower environmental impact quotient (EIQ) toxicity rating—15.3—than organic sprays like insecticidal soap (19), horticultural oil (27.5), pyrethrin (39) and Bordeaux mixture (67.67). (The EPA determines EIQ, a scale of 0 to 100.) Glyphosate works only on growing plants and it is frequently chosen by land-conservation agencies because of concerns about wildlife.

Applied responsibly, glyphosate enters green leaves and stalks, travels to the roots and kills most plants in a week or two by inhibiting amino-acid production. Then, soil microorganisms quickly break down glyphosate into non-threatening phosphorus and amino acids. Correctly applied, glyphosate is not a danger to pets, children, beneficial insects or other wildlife.

According to Jeff Gillman, a professor of horticulture at the University of Minnesota who writes about glyphosate in his useful book The Truth About Organic Gardening, some of the most worrisome-sounding studies on glyphosate have not been supported by follow-up research. Some news reports, such as the effect of glyphosate on villagers in Columbia and Afghanistan, stem from crop dusters incorrectly and unconscionably dumping the stuff not just on fields of narcotics, but on villages, too. On his shared blog,, Gillman says, “I can’t find any reason to think that glyphosate is anything but what it appears to be—an effective weed killer that is on the safer end of the spectrum relative to other chemical weed killers (and here I’m including organic weed killers too. Ever been exposed to those 20-percent acetic-acid vinegar herbicides? I tried one this summer—just being near it made my eyes burn.)” [From "The New Evidence Against Glyphosate," 9/23/2010.]

Safe use

In the same way that household products like gasoline and alcohol should be used responsibly, there are a few rules for using glyphosate. Don’t get it on anyone. Don’t spray on a windy day—it’ll land on garden plants and kill them. Don’t spray before a rain, as it will just wash off. Don’t spray near bodies of water, because the soap-based “inert ingredients” that come with the glyphosate will kill amphibians. Don’t use brands that promise plants will look dead in 24 hours. They include additional herbicides that might destroy the leaves before the glyphosate is carried to the roots, meaning the weeds will ultimately survive. Don’t fail to read the directions or follow them closely.

I have one good-quality pump sprayer that is used only for glyphosate. I keep a plastic measuring cup with the bottle of concentrate so I can add the right amount; following the instructions, I use a stronger concentration for perennials in summer than for annual weeds in winter. After pouring the herbicide in the sprayer, I completely submerge the end of the hose so that the mixture doesn’t foam up and overflow. I adjust the jet so that the spray comes out in drops rather than a mist, so it doesn’t travel as far.

I use glyphosate once a month during the growing season, which for me can be year-round during a mild winter. On our one-sixth acre lot, it takes about 20 minutes. Applications this frequent actually let me reduce the total amount of glyphosate that I use. Why? Weeds that germinate between applications are quite small and haven’t flowered, much less set seed, by the next spraying. A tiny spritz on one or two leaves will kill such a small plant. I just tap the trigger to see how small a quantity I can spritz on the weed. Also, by killing weeds before they can set seed, I’m slowly reducing the weed-seed inventory in my garden.

For full-grown perennial weeds with deep roots, like wisterias and ivies, the first spray hardly shows any results. But with the next month’s spraying, tough, mature perennial weeds either die or shrivel up. A third or fourth spraying does the trick for the toughest perennials.

For weeds that are growing within the skirt of a garden perennial, I do a quick hand pull if I think I can get the root out. But if the plant is too big or the ground, too dry, I either use my foot to push some of the garden plant’s skirt aside so that I can spritz a weed leaf or two (with the sprayer aimed away from the garden plant); or if the weed is tall enough, I use my foot to bend it down to the ground, beyond the canopy of the garden plant, so that I can spritz the top leaves safely. If you accidentally spritz a garden plant, quickly rinse it off or snap off the affected leaves right away.

The first time you spray weeds with glyphosate may take a while. Subsequent sprays will take less time, because you’ll have fewer and smaller weeds to contend with. You’ll be able to dedicate the time you save on weeding to more enjoyable activities like dividing, pruning and planting. Better yet, you’ll have time for just relaxing in the garden with friends on a bench, rather than toiling alone on your knees.