We hear a lot of advice to use table salt as a weed killer, and it appears in many home garden recipes. But, does it work? And, is it good for the garden? Should we use it? Here’s what you need to know before pouring it on.
This is part of series where we explore popular garden myths we have all fallen for and fact-check common garden advice.
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.
But a lot of this information is shared without answering these basic questions:
- Do they really work?
- And, if they do, what are the side effects?
- Will they do more harm than good?
- And, 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.
- Table Salt in the Garden
- How Sodium Affects the Environment
- The Role of Other Salts In The Garden
Table Salt in the Garden
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.
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 Bibilical stories, you may have heard the famous story 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.
Because salt lowers the freezing point of water, it has also 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
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.
The question is whether it’s something that we should be pouring or spraying in our gardens and, ultimately, into our soil.
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, afterall—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, 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 hundreds of 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.
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.
- 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 ♛
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