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Garden Myth: Salt Makes a Good Weed Killer

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Salt will kill anything that grows … but that doesn’t mean it’s a good herbicide! Source: mzayat.com & fortcollinsnursery.com

Actually, this is both true and a myth. Salt really does make a great weed killer (herbicide), as it will kill just about anything that grows, but is so toxic it simply can’t be recommended in most garden settings.

Salting any type of planting will kill plants for months, years, even decades: a sort of scorched earth policy for plants of all sorts, leaving the ground absolutely barren for ages. The Romans are said to have salted the earth at Carthage in 146 BC* in order to destroy any chance of that civilization rebuilding. It’s that efficient at killing plants!

*That, in fact, probably never happened: salt was too valuable a commodity at the time to waste spreading thickly over fields! But it would have worked had they done it.

Even the much-hated herbicide RoundUp (glyphosate) pales in comparison to salt when it comes to environmental damage. At least glyphosate does decompose; salt never does.

How Salt Works

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When soil is salted, water will move from the lesser concentration of salt inside the root tissues to the greater concentration in the soil outside, causing cells to wilt then die. Source: laidbackgardener.blog

Salt kills plants by osmosis. Where there is more salt outside of the plant than inside, it will draw the water out of nearby plant cells, causing leaves (if applied by spraying) or roots (if watered in) to dry out and die. If you spray salty water on most plants, the leaves and possibly stems will soon turn brown, but they’ll probably soon put out new growth, as salt is a contact herbicide: it doesn’t travel through the plants’ vascular system and therefore only kills the tissues it touches. If it is watered into the soil, though, and kills the roots, that will kill the whole plant.

Salt also kills most soil organisms, both good and bad, including bacteria, fungus, insects, earthworms and slugs.

The Poison Is in the Dose

Of course, we humans use table salt all the time and we’re fine with it. So are plants… when the salt is highly diluted. In fact, both plants and animals (including humans) need both sodium and chlorine (table salt is sodium chloride: NaCl) for healthy growth … but only in small amounts.

Take a look at how many plants grow on the edges of bodies of water with high salt concentrations, like the Dead Sea or Great Salt Lake. There aren’t any, are there? Neither body of water has any fish either: they’re too salty.

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Here, de-icing salt has killed the grass near the road. Treating any surface with salt will have the same effect. Source: turfgator.com

How much salt is too much? I hesitate to recommend ever using salt as a herbicide, so in fact the dose matters little. Even if you apply salt to kill weeds on a patio, sidewalk or parking lot where no growth at all for several years would be a benefit, remember that the salt applied will eventually be diluted by rainfall and soak into the water table or run off into nearby bodies of water. If everyone started doing this, it could eventually render the water locally unusable. Already, the use of road salt is causing salt levels in ground water and nearly bodies of water to skyrocket near many cities, a disaster for the environment; gardeners blithely salting weeds would just make things worse.

Where You Never Want Plants to Grow

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Salt certainly will kill weeds growing in walkways, but are you willing to pay the environmental price? Source: www.inchcalculator.com

I simply don’t recommend using salt as a herbicide, especially in or near gardens, lawns, other plantings or where there are tree roots. If you insist on using salt to keep weeds down in pavement or in cracks in a driveway or sidewalk, places where you never want to see plants grow, make sure to at least keep well away from anything growing. If, under your conditions, you’re sure that the salt will not reach the water table, you can spread a thin layer of rock salt (de-icing salt) in between bricks, pavers or stones to keep weeds away for years. Or dilute table salt or rock salt in water (about 3 parts salt per 1 part water), mixing until it dissolves, then (carefully) pour it on. But you’re playing with fire!

Be forewarned that salt is also highly destructive to concrete and paving stones, so by solving one problem, you might be causing another.

Oops!

You’ve accidentally spilled salt on plantings? Soils can take years to recover if left on their own, but if you water regularly, this will gradually dilute the salt causing it to flow elsewhere.

I don’t recommend using salt to kill plants. Salt may be cheap, efficient at killing plants and even organic (hey, it’s a natural product!), but I feel the potential damage to the environment is just too great!

Learn to tolerate a few weeds rather than kill them. Then everyone will be better off!

Garden writer and blogger, author of more than 60 gardening books, the laidback gardener, Larry Hodgson, lives and gardens in Quebec City, Canada. The Laidback Gardener blog offers more than 2,500 articles to passionate home gardeners, always with the goal of demystifying gardening and making it easier for even novice gardeners. If you have a gardening question, enter it in Search: the answer is probably already there!

10 comments on “Garden Myth: Salt Makes a Good Weed Killer

  1. Each year, our front yard is damaged by the sodium chloride applied to the road during the winter months. It use to be a small stretch along the edge of the property, but now it is huge swaths that are just dead and only turn green when weeds fill in. Ugly and no hope for change.

    • If I were you, I’d give up on lawn in such spots and go for something else. Even mulch would be better than dead grass. There are a few salt-resistant groundcovers and shrubs, however, how well even they would tolerate yearly assaults at such concentrations, I don’t know.

  2. Pingback: Can You Use Vinegar as a Weedkiller? – Laidback Gardener

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  4. It would have been of great benefit to others like myself, that found the article helpful – even changing my mind on using salt for my herbicide – but lack the knowledge for what an organic yet environmentally responsible option may be.

  5. I’m building a 60×60 area in my backyard for a dog play area, it will be fenced and have about 4″ of sand- 35-40 tons and I dont want ANYTHING growing up thru the sand or the fence- including the half dead grass that was there before I scraped most of it off. I dont want roundup or toxic chemicals around the dogs or myself, so I spread out 80 pounds of rock salt on half of the area to start with, 2 more bags will take care of the other half, and the 35-40 tons of sand over it should take care of the grass and weeds there forever!

    Most of the area had an old gravel drive around it that I had covered over with 2-3″ of dirt from excavating under the house 20 years ago, the grass seed I put in back then grew but not real well, so I’m glad to be rid of it now.

    • Problem is seeds will fall from the sky, land and germinate right on top of the sand.

      • Yes, but I’m not naive to think that can’t happen, I plan on annual salting with rock salt and contuing to spray with a super strong solution of salt, vinegar, bleach, dish soap, and muriac acid, the muriatic acid used full strength with the other stuff mixed in burns up weeds in minutes, they lose color and shrivel up. There’s no nutrients for plants/weeds in sand, they can try sprouting but have to reach soil to really survive.
        There’s no other alternative since I’m not willing to use cancer causing chemicals around my dogs or myself like “Roundup” which has lots of class action lawsuits filed against it for non hodgkins carcinoma. The muriatic acid starts bubbling up the minute it hits the weeds and the dark green color starts turning light yellow as the stem and leaves star shrivelling up, I saturate around the stem good.

  6. “Your choice. I would suggest the salt is actually more environmentally harmful that Roundup, however, but that is arguable.”(Larry)

    Roundup Maker to Pay $10 Billion to Settle Cancer Suits

    Bayer faced tens of thousands of claims linking the weedkiller to cases of non-Hodgkin’s lymphoma. Some of the money is set aside for future cases.

    Edwin Hardeman had struggled through six rounds of chemotherapy in 2015 when he saw a TV report that said exposure to a popular weedkiller could lead to the exact cancer that was destroying his life. For the first time, the Californian had a possible explanation for his disease.

    What he didn’t know then was that four years later, he would become the first person to prove in US federal court that Roundup had caused his non-Hodgkin lymphoma (NHL) – and that in the process, he would help uncover damning secrets about the manufacturer, Monsanto, and its influence in science and government.

    “I hope this is a significant turnaround in Monsanto’s history,” Hardeman, 70, said on a recent morning in his Windsor living room, his first interview since a jury ruled that the company was liable for his cancer and owed him $80m in damages. “Maybe they will finally do the right thing.”

    Monsanto first put Roundup on the market in 1974, presenting the herbicide, which uses a chemical called glyphosate, as a breakthrough that was effective at killing weeds and safe. The product has earned the corporation billions in revenue a year, and glyphosate is now ubiquitous in the environment – with traces in water, food and farmers’ urine.

    …despite Monsanto’s best efforts, the judge ordered the unsealing of key internal company documents that emerged during discovery – records which, for the first time, revealed Monsanto’s conduct behind closed doors.
    Uncovering Monsanto’s strategy: ‘I was appalled’

    The unsealed emails and documents suggested that Monsanto had an aggressive PR strategy for years that involved attacking negative research and ghostwriting and pushing favorable studies.

    In one email, a Monsanto executive advised others in the company to be cautious about how they describe the safety of the product, warning: “You cannot say that Roundup is not a carcinogen … we have not done the necessary testing on the formulation to make that statement.”
    Monsanto officials also privately talked about the company writing science papers that would be officially authored by researchers, with one email saying: “We would be keeping the cost down by us doing the writing and they would just edit and sign their names.” The internal documents also shined a harsh light on Monsanto’s cozy relationship with US regulators and its media campaign to combat the Iarc ruling.

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