Epsom salt (magnesium sulfate) is frequently recommended as a plant fertilizer but it’s rarely lacking in home gardens and the excess harms waterways.
This is part of a series on common garden myths where we examine popular garden tips.
The Epsom Salt Garden Myth
You’ll hear gardeners gush about the benefits of Epsom salt (magnesium sulfate) as a solution for, well, pretty much everything: more vibrant flowers, greater yields for veggies, better seed germination, increased nitrogen uptake, vitamin production, sweeter tomatoes, pest control, weed control, greener leaves and so on and so on.
Well, who wouldn’t want to use something so amazing in their garden?
Only problem is, there’s really no evidence for any of this. And, the excess causes harm to our waterways.
Let’s dive into the facts and help spread the word.
Contents
- What is Epsom Salt?
- Why Soil Tests Are Helpful
- Environmental Concerns
- Correlation Is Not Cause
- Resources
What is Epsom Salt?
Epsom salt is magnesium sulfate. It’s a white, crystalline water-soluble solid. This is the formula for household Epsom salt: MgSO4·7H2O
In agriculture, magnesium sulfate is used to correct magnesium deficiencies in the soil.
It is not recommended for home gardens because they are rarely magnesium deficient and excess can cause environmental issues.
Is it possible to join an online garden forum and not hear Epsom salt recommended over and over again?
This is a classic case of gardeners spreading anecdotal tips that sound easy— and Epsom salt marketers delighting in it—but the fact is that there is not any science behind it.
And the claims are easy to debunk.
Yes, Epsom salt will add magnesium and sulphur to your garden. That’s true.
But the chances are your garden soil is not deficient in either of these things. And this means your soil and plants don’t need it.
Period.
It’s basic science.
There are specific applications in agricultural settings where mono crops seriously deplete farmland of its magnesium, but this does not translate into everyday use in home gardens. We do not grow that intensely and a soil test will show you if any nutrients including magnesium are at low levels. Odds are, it’s not.
Does Epsom Salt Fertilize Plants?
As a fertilizer, Epsom salt is very limited. It don’t provide any nitrogen, phosphorus or potassium—the macro-nutrient NPKs of fertilizers.
It does provide magnesium and sulphur, which, as we discussed, are rarely deficient in home garden soil and are not in high demand by your plants. Adding more will likely be of no benefit. And certainly not cause some miraculous growth spurts or fruiting like many claim.
Is Epsom Salt a Harmless Weed Killer?
No. This is another myth.
As a weed killer, along with the dish soap and other household items suggested in countless homemade weed killer recipes online, take a step back and consider what it is you are putting into both your garden and the environment.
The only thing Epsom salt myths do is sell Epsom salt.
Just because it’s in your kitchen cupboard does not make it safe, beneficial, or harmless for the garden. And there are no specific properties in these things that target weeds.
Basically, it’s the same as tossing a bunch of random things in the garden and hoping they somehow smother the problem. Think of it like throwing garbage on your weeds. It’s all stuff that has no business in a living, thriving garden.
To me, the Epsom salt garden folklore does nothing more than sell a lot of Epsom salt.
Why Soil Tests Are Helpful
If you are wanting to improve your soil, a soil test by a local laboratory can help determine any deficiencies.
Otherwise, if you keep your garden soil fed with annual applications of compost, soil quality at a micronutrient level may not ever be an issue.
Container plants may need fertilizing and there are plenty of organic products on the market that contain the actual nutrients your potting mix may be deficient in. Epsom salt will not do this.
Environmental Concerns
Consider the big picture.
Theoretically, you could even do harm to your garden by adding too much Epsom salt—excess magnesium can create deficiencies in other nutrients—and Epsom salt is highly soluble, which means it can get into groundwater where it ends up in rivers and lakes, and that’s not good for the environment.
It may be trivial for one gardener, but imagine thousands or millions adding Epsom salt. That adds up. Mass agriculture has shown us this.
And, that’s on top of the environmental costs of producing and distributing the Epsom salt in the first place. All for something that will likely do no good in your garden.
What about bathing in Epsom salts? Aches and pains aside, think about where it’s going—right down the drain into our water systems. Again, not helping the ecosystem.
Not what some want to hear, but that’s how it goes.
Correlation is Not Cause
If you grow beautiful roses or fabulous tomatoes and you did add Epsom salt to the soil, it might be easy to convince yourself it was the cause.
But the best evidence we have says Epsom salt does not deserve the credit you may be giving it.
If nothing else, the roses (or tomatoes or whatever) probably did well despite it. This explains the problem with anecdotal evidence if you’d like to read more.
The fact that no researchers can duplicate these results and professional growers don’t use Epsom Salt is a big hint that something else contributed to your success.
If you know someone who swears by it, see if they’ll consider following all their other good plant care habits minus the Epsom salt. Or at least some side-by-side testing.
It’s the basics like adequate sun, water, air, healthy soil, and the plant itself that work in harmony to create optimum growing conditions.
Unless there is a proven magnesium deficiency, which we know is uncommon, they can spend their garden money elsewhere and still have healthy plants.
I’d love it if there were magic solutions and easy answers for everything too, but gardening and life have other plans.
The Epsom salt craze is just one of those pesky garden myths that never seems to fade away. Hopefully one day the truth will set it free.
Resources
Listen
Read More
- Epsom Salts are Not Recommended: Unnecessary, Potentially Damaging | University of Saskatchewan
- Epsom Salt Use in Home Gardens and Landscapes | PDF format | Washington State University Extension
- The Epsom Salt Myth | NDSU
~Melissa the Empress of Dirt ♛