The advice to use Epsom salt in the garden is the top garden myth that never goes away. The internet is filled with articles and anecdotes about how great they are for your plants but it’s just not so. Epsom salt is just magnesium sulfate and the average home garden has no need for it. Save yourself some money and just stick to proven growing practices for healthy plants.
This is part of a series on common garden myths and advice, and what the facts show.
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.
- What is Epsom Salt?
- Why Soil Tests Are Helpful
- Environmental Concerns
- Correlation Is Not Cause
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 because there is not much to it.
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.
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 every day use in a home garden. 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 (see more on Fertilizers for Organic Gardeners here).
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. And 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.
Containers plants may need fertilizing and there are plenty of products on the market that contain the actual nutrients your potting mix may be deficient in. Epsom salt will not do this.
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.
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 is that 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 them is a big hint that something else contributed to your success, not the Epsom salt.
If you know someone who swears by it, see if they’ll consider all the 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, 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.
And no, smothering weeds with a bunch of household stuff is not a recommended solution either. If you want to read more, see What Vinegar Really Does to Weeds and these 7 Weeding Tips Every Gardener Should Know.
I’d love it if there were magic solutions and easy answers for everything too, but gardening and life have other plans.
- 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 ♛