Table Salt as a Weed Killer: Why It’s More Harm Than Help

We hear advice to use table salt as a weed killer and see it recommended in recipes for diy weed treatments. But it’s not that simple. Even though salt is “natural,” it is not harmless. Excess salt causes tremendous damage to nature and our ecosystems.

This is part of series where we explore popular garden myths we have all fallen for and fact-check common garden advice.

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Is Table Salt Good for the Garden?

It seems like just about anything we find in our kitchen has been heralded as great for our garden—as herbicides, pesticides, fertilizer, or other uses.

There is this longstanding idea that because we use something daily in our home—and, like salt, is found in nature—that it must be beneficial or harmless in the garden.

But this is not so.

Salt (sodium chloride) is indeed natural but, when levels are excessive, it causes tremendous harm to soil and water.

You might think, what’s the harm if I use a little in my garden to try and kill some dandelions? Can’t I just spray some on my driveway or patio?

But the fact is, these diy weed killer remedies are shared by millions of gardeners—and that’s a lot of salt (and other substances like dish soap) being introduced into nature where it does not belong.

Ultimately, as gardeners and stewards of the earth, we want our choices to benefit the ecosystem as a whole.

So, when thinking about using salt or anything else, these are helpful questions to ask first:

• Does this belong in the garden?
• How will it affect the ecosystem? What are the long-term effects?
• Is this necessary? Is there a better way?

Because, if you’re like me and you want to garden with nature and the environment, not against it, there’s no such thing as choices made in isolation.

Treating one problem only to cause another is not really a good solution at all.

Yes, table salt may kill weeds, but also does greater harm.

Contents

• Table Salt in the Garden
• How Sodium Affects the Environment
• The Role of Other Salts In The Garden
• Resources

Table Salt in the Garden

Toxic Effects of Salt

One of the most popular recipes online for homemade weed killer calls for some combination of vinegar, dish soap, and salt (sodium chloride) or Epsom salt (magnesium sulfate).

We’ve already discussed the effects of vinegar in the garden here and what dish soap does to plants here, which ranges from useless to harmful depending on the application.

If you’ve studied history, at first glance, table salt seems like an unlikely candidate for gardening. There are stories going back thousands of years of salt being used in a vindictive way to destroy agricultural land.

In addition to Biblical stories, you may have heard of the Romans salting the farmland of Carthage. That’s more folklore than history, apparently, but we’ve long known about the toxic effects of salt.

Today, we are dealing with the side effects of modern-day applications.

Because salt lowers the freezing point of water, it has been used for many years to de-ice winter roads.

But now, knowing the environmental damage caused as it gets into our fresh waterways, many communities are seeking alternatives.

And all of that connects to why it’s questionable for home garden use as well.

How Sodium Affects the Environment

Table Salt

The salt we’re talking about is table salt. Sodium chloride (NaCl). The stuff in your salt shakers and in bags of salt at the grocery store.

While not part of this discussion, Epsom salt—not the same as table salt— is not a good solution in the garden either.

So, there’s no question that salt kills plants including weeds. In fact, it is not selective so it will affect whatever it touches—weed or not.

The more important point is whether it’s something that we should be pouring or spraying in our gardens and, ultimately, into our soil and waterways.

Because it’s a kitchen product that we put on our food, there’s a perception that it’s environmentally friendly.

It’s 100% natural and lets you avoid putting harmful chemicals in your garden—they say!

If you suggested pouring acetic acid and sodium chloride into gardens, you’d get resistance, but “vinegar” and “salt” sound much more innocent.

But salt isn’t harmless—especially the sodium ion you’d be releasing into your soil.

And, of course, there’s no such thing as a harmless herbicide—it is killing something, after all—but some are more harmful than others.

Sodium is Toxic to Most Plants

Sodium is a toxic metal. Very toxic to most plants. And, while vinegar will evaporate (but can cause other issues), the sodium stays around—but not necessarily where you put it. It can get washed into any other part of your garden, and on to puddles, streams, rivers, and other waterways.

While a small amount of salt isn’t going to ruin your garden or the environment, if you’re using enough to kill your weeds, that adds up.

And then multiply that by millions of gardeners around the world, and it’s hard to recommend salt as environmentally-friendly or harmless.

So, can salts kill weeds? Yes.

Are there negative side effects? Yes.

Would I use it in my garden? Nope.

The Role of Other Salts In The Garden

As a gardener, it’s helpful to understand the difference between table salt (sodium chloride) and other salts.

Chemists Define “Salt”

The word “salt” has been in the English language for centuries and it’s one we all know and use.

But, in the late 18th century, chemists came up with a new, more scientifically precise definition of salt. And with that new definition, what we know as salt—the stuff from salt shakers, also known as table salt (sodium chloride)—was just one of hundreds of salts.

And this has been causing confusion ever since. When someone is talking about salt, do they mean table salt or chemical salts in general?

It can be a particular problem in gardening, because one of those salts is definitely bad for the garden and can kill plants, while the other includes things that can help plants, as long as they’re used properly.

The Importance of Ions

Chemically, salts are a combination of two or more ions, which are atoms or molecules with an electric charge, either positive or negative. When they come together in a salt, those charges cancel each other out and the salt has no net electrical charge.

Almost all of the nutrients that plants take up from the soil are in the form of ions. We call them by their elemental names, but what plants actually take up are those elements in ions.

So, for example, we talk about plants getting nitrogen from the soil, but what they actually take up are nitrate—a negatively charged ion—or ammonium—a positively charged ion.

Related to this, the pH level of soil—a measure of the concentration of positively-charged hydrogen ions in the soil—changes how or if plants can take up nutrient ions.

Salt Examples

Table salt (sodium chloride) is a positively charged sodium ion and a negatively charged chloride ion, so it follows the same pattern.

Epsom salt is a form of magnesium sulfate (MgSO₄·7H₂O), combining a positively charged magnesium ion and a negatively charged sulfate ion. And both magnesium and sulfur are essential macronutrients for plants.

Ions In Soil

Chemically, salts are comprised of ions, and most of our plants’ nutrients are ions. We want those ions in our soil.

Most of them are already there in sufficient quantities (there’s very little chance that your soil has a sulfur deficiency, for example), but if a soil test confirms that we need to add some plant-accessible nutrients to the soil, a quick way to do so is in the form of salts that will almost immediately dissolve into their ions once they contact moist soil. That’s what synthetic fertilizers do. They are usually comprised of chemical salts that quickly become ions in the soil.

But not all ions are nutrients—sodium, for example, is not only not a nutrient but it can harm plants. And even nutrient ions can become a problem if there’s too much of them—particularly if there’s too much of some of them and they get in they way of others that plants need too.

So, when it comes to your garden, you can’t generalize from table salt (sodium chloride) to all salts. Sodium is bad for plants but most other salts don’t include sodium and some are comprised of nutrients that your soil needs for your plants to be healthy.

What should I use instead?

Removing weeds—which are unwanted plants—is both an art and science.

While certain invasive species can be very difficult to remove or eradicate, it is helpful to learn about the plant you are tackling to understand how and when it reproduces or spreads. That’s key information for knowing the best way to stop it.

These deweeding tips for home gardeners should help.

There are no perfect answers or solutions but at minimum it’s rewarding to make choices that avoid causing environmental harm.

Resources

Listen

Read More

• Environmental, Health, and Economic Impacts of Road Salt | New Hampshire Department of Environmental Sciences
• The Impact of Salts on Plants and How to Reduce Plant Injury from Winter Salt Applications | UMass Amherst
• Effects of Weed Killer Made from Vinegar and Salt | Oregon State Cooperative Extension
• Why Dandelions Are So Misunderstood (Whether You Like Them Or Not) | Empress of Dirt

~Melissa the Empress of Dirt ♛