Does Epsom Salt Benefit Tomatoes, Roses, and Garden Plants?
Some gardeners swear by Epsom salts as a gardening hack. We’re here to tell you that Epsom salts are good for neither plants such as tomatoes or roses—nor the soil. Yes, it’s one of those gardening myths. Learn more—and let’s talk about alternatives.
Most gardeners love a reliable home remedy and are eager to embrace a magic bullet. This is the case with Epsom salts. They are supposed to make flowering plants bushier and blossom more and make peppers and tomatoes more productive. But are they really a miracle cure-all? Can Epsom salts be harmful? Let’s separate fact from fiction.
What Is Epsom Salt?
Epsom salt is the chemical magnesium sulfate (MgSO4)—which means both magnesium (about 10%) and sulfur (about 13%).
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- Magnesium is needed by plants to generate the chlorophyll needed for photosynthesis. On a plant lacking magnesium, the older leaves will turn yellow between the veins and along the edges, and growth will be stunted. Sandy, light, low pH soils are prone to magnesium deficiency. If your soil is quickly leached by rainfall and has a pH of 5.5 or less, it probably lacks sufficient magnesium. Adding compost to raise the level of organic matter in the soil will help.
- Sulfur is needed to form some vitamins and plant proteins. If a plant lacks sulfur, its young leaves will turn yellow. Sulfur also gives vegetables such as broccoli, onions, and mustard greens their flavors. Sulfur is seldom deficient in garden soils in North America, so deficiencies are rare. Plus, if sulfur is overdone, it will build up in the soil and make it hard for plants to use the other nutrients they need. If you are lacking sulfur, manure is a good organic source.
Is Epsom Salt Good for Plants?
Bottom line: No, Epsom salt is not beneficial for plants.
- One reason people use Epsom salts is to prevent blossom-end rot. This isn’t true. In fact, Epsom salts can be harmful! Why? Blossom-end rot is caused by a calcium deficiency, not magnesium or sulfur deficiency. Adding too much magnesium to your soil can actually prevent calcium uptake!
- While many vegetables (leafy greens, beans, peas) can grow in soil with low magnesium levels, other plants, including tomatoes, peppers, and roses, need high levels of magnesium. So what if Epsom salt is added to the soil to correct large soil magnesium deficiencies? Unfortunately, horticultural studies (Auburn University, Delaware Valley College) prove that adding Epsom salts to the soil (directly or through watering) does not link to higher yield or healthier growth from peppers and tomatoes to roses. When it comes to your soil, do not rely on Epsom salts to adjust deficiencies in magnesium or sulfur! The only real way to know if your soil is lacking magnesium or sulfur is to test your soil. Here are 3 simple DIY soil tests. (Or, there are soil tests provided by your cooperative extension.) If you add Epsom salts to soil that already has sufficient magnesium, this can harm plants and contaminate the soil.
- In addition, spraying Epsom salt solutions on plant leaves can also cause leaf scorch. Excess magnesium can also increase mineral contamination in the water that percolates through the soil. Remember that Epsom salt is a highly soluble chemical. When you use Epsom salts on plants, they will leach out of your soil fast, running into and polluting ponds and streams. The best practice is to avoid adding any extra chemicals to your soil—even things that seem ‘safe’— because you can easily do more harm than good.
Alternatives to Epsom Salt in the Garden
Before heading to the drug store for some Epsom salts, look for a slow-release form of magnesium that will have longer-lasting effects, such as magnesium-enriched biochar or kieserite. If your soil is acidic, dolomitic limestone will raise the pH and add magnesium.
Save the Epsom salts to soothe your tired, aching body after a day in the garden!
Read more about gardening myths!
Have you ever used Epsom salt in the garden? What was your experience?
Robin Sweetser
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I my part of the world, the desert southwest, Miracle Grow is not as effective as it is in kinder soils. The additives we need in our depleted soils is that provided by FertiLome or Carl Pool.
I use epsom salt to treat the snow and ice on my porches. The grasses near the porches are greener and look healthier in the spring. Have used the salts for years without problem as a sprinkling along with compost. Doesn't seen to cause problems.
I have my doubts about the university study cited in this article to suggest Epsom salts are of no value to roses. What is true in the area where testing/study occurred might not be hold up in a different gardening/soil environment — of which there are MANY in the United States.
With Epsom salt, I can visibly see the difference in my roses in the form of more growth and healthier looking leaves. (I have also seen it do wonders for citrus trees.) As the old saying goes, however, "Your mileage may vary": Gardeners in other states may or may not notice similar results because their soil is higher quality to begin with. Not so where I live. I live near a seasonal lake that is covered in white residue when it dries out — presumably evidence of calcium/potassium abundance in the soil. The well water in the area is filled with so much iron, I have to filter it to drink it. The sandy soil in my area is presumably also very alkaline (can't grow a camellia or blueberry bush to save my life no matter how much I attempt acidify the soil).
To be perfectly honest, after relocating from a coastal zone to the High Desert (Zone 9), I have found Epsom salts more useful in a pinch than the County cooperative extension (would love to try soil testing but can't raise anyone on the phone who seems to know where to point me. Phone tag is about as good as it gets here in LA County. I've even tried writing to UC Davis and UC Riverside with no success).
The notion that Epsom salts may accumulate in such vast quantities to become an environmental pollutant seems amusing to say the least. It is one of the least processed substances one can apply to plants, compared to the many chemical-based fertilizers sold in garden centers. I have never heard of "magnesium runoff" spoiling water tables, whereas I have heard plenty about contamination tied to nitrates linked to agriculture, septic systems and the like (i.e. "blue baby syndrome").
In conclusion, just as it is possible to over- or under-apply a "balanced" fertilizer, it is possible to over- or under-use Epsom salt. Debate about whether it is harmful or helpful is about as useful as saying a balanced fertilizer is "beneficial" — without the caveat of how often or how much! It's a matter of common sense, really. In moderation it can't hurt — and if it helps one will observe the results soon enough.
These days, "science" is defined as that which almost always runs directly contrary to the decades long, direct personal experience of hundreds of thousands of people, yet someone has a piece of paper in a frame on their wall so, they still insist they're right.
Using epsom salts on my ailing tomato & pepper plants was a game changer for me. The change in my lettuces and brassicas was profound. It's use has been nothing but beneficial for me.
The "Universities" can make all the proclamations they want, I will never stop using it.
Do your own soil test..they have a how-to on almanac's site here.
