The Use of Epsom Salt to Boost Your Plant’s Growth
A popular old-time gardening tip is to put Epsom salt on houseplants and outdoor plants to give them a healthier look and feeling for longer. A lot of gardeners swear by it, while other critics point out there are no reliable scientific studies to back up their claims.
Have you ever soaked in a warm tub generously laced with Epsom salts? If so, you know how powerful they are. Using them soothes sore muscles, softens water and frees you from the stress of a hectic day. In spite of the fact that Epsom salts resemble gritty, fine salt, they actually contain magnesium and sulfur.
A farmer in Epsom, England noticed in 1618 that his cows were not as fond of drinking from a nearby spring. Having tasted it, he decided it could be used better as a spa, and Epsom soon gained its reputation as a bathing destination.
Generations of gardeners say this skin-softening, anti-stress compound has a direct connection to gardening. Meanwhile, Dr. Linda Chalker-Scott, Associate Professor and Extension Urban Horticulturist at Washington State University adds, “Increasing the level of magnesium and sulfur is not a sensible approach, especially in the absence of any signs of deficiency.”
At best, these claims are anecdotal, and likely to have a detrimental effect on the planet, especially if everyone jumps on the Epsom Salt bandwagon.
What is Epsom Salt?
Magnesium sulfate belongs to a class of compounds that contains sulfur and oxygen, having the formula MgSO. Epsom salt is typically found as the heptahydrate sulfate mineral epsomite (MgSO O), which is also commonly known as Epsom salt. Epsom salt is composed mostly of magnesium, sulfate, and some water.
Although magnesium is an essential nutrient to plants, it is a minor element that means they require very little of it. And most soils, especially in the midwest and western states, have plenty of magnesium in them.
The sulfate molecule is absorbed directly by plants and is used by the sulfur molecule. It is also a minor nutrient for plants. You will find that most composts and organic fertilizers contain more than enough magnesium if you use them as top dressings or amendments in your garden. Additions in the form of Epsom salts are counterproductive.
It was never intended to use Epsom salts on plants.
The Magnesium Issue
Spray Epsom salts onto your houseplant’s leaves, dissolve it in your watering water, or toss it into each planting hole. Some Epsom salts users claim the salts will produce healthier, greener plants. However, it is hard to find scientific studies that support such claims. Magnesium and sulfur are indeed essential for plant growth and health.
Both minerals are present in most soils, even in potting soils. Leaching or eroding of soils can deplete magnesium, and soils used for potting can also lose magnesium over time (long-term leaching). For a garden, soil testing may be useful for detecting mineral deficiencies, but not for houseplants.
In response to feedback from backyard gardeners, the National Gardening Association conducted a study to test the effects of applying an Epsom salts foliar spray. The results concluded that applying Epsom salts solution to plants during the growing season made the foliage greener, bushier and resulted in more blossoms.
Despite this, Dr. Linda Chalker-Scott, PhD, associate professor and urban horticulturist for the University of Georgia, is skeptic. According to her, both magnesium deficiency in the soil and intensively produced crops are crucial for Epsom salts’ success in studies like hers. If this is not the case, it could do more harm than good, Chalker-Scott says.
Epsom salt cure blossom end rot
Although many claim that adding Epsom salt to your soil prevents blossom end rot, you will be shocked to learn that this isn’t necessarily the case. Blossom End Rot is caused mostly by inadequate calcium uptake and not by low magnesium levels in the plant.
The Michigan State University extension has a great quote about Blossom-end rot. “Insufficient calcium in the tomato’s tissue causes rot. Calcium gets into the plant through its roots, which tend to locate it in just one part of the plant. Soil, stems, leaves, and plants can become rotten even when there is a large supply of calcium. Plants that are actively growing such as developing tomatoes need regular calcium to prevent these spots from forming.”
“Inconsistent soil moisture for every part of the growing season is a contributor to blossom-end rot. As calcium is only transported into the plant when there is a sufficient moisture supply, it will be affected by a calcium deficiency when drought occurs.
Adding Epsom salt to the soil may produce more rot since magnesium and calcium ions compete for uptake into the plant. The more magnesium in the soil, the less calcium will be found.
Calcium and magnesium are in competition with one another, and if one is out of balance, the plant and fruit suffer. How can you prevent blossom end rot then?
The soil can withstand extremes in moisture and dryness by adding mulch and maintaining regular irrigation.
Over fertilization may also lead to BER, especially when amino compounds such as ammonium nitrate are used (ammonium nitrate and 10-10–10). Ammonium works in competition with calcium for calcium uptake.
Tomatoes should be green, but not lush. Lush tomatoes are more susceptible to rot since their foliage takes up calcium before the fruits get to it.
It should be noted, as well, that sometimes soils that are extremely acidic prevent plants from using magnesium efficiently. An easy and long-lasting fix for that is to add organic matter. Garden limestone is another.
Epsom salt cures chlorosis
Nope. It is true that the chlorophyll molecule has magnesium in it. Consequently, treating chlorosis with additional magnesium (Espsom salts), since most soils are not lacking in magnesium, would be useless.
The most common cause of chlorisis is iron deficiency in the soil. The best thing to do is use Iron supplements in your garden. If you add magnesium instead of iron, you are only causing the problem to worsen.
Epsom salt deters pests
Not even close. I read somewhere that if you sprinkle Epsom salt around garbage cans, raccoons will avoid your trash because they don’t like the taste.
In addition, the most important thing about Epsom salt is what it does! Here’s what I want you to read … What possible harm can it do to your garden?
As we have learned, magnesium is usually not deficient in soil, but what would be the harm in using it? Many gardeners swear by it! An immediate danger is the imbalance of nutrients in the soil, which is counter to what we as gardeners all want. Your best garden recipe for success is a well-balanced soil.
Plants can suffer from potassium deficiency if magnesium sulfate levels are too high. Using Epsom salts unnecessarily will not result in better plant growth but can actually cause the plant to suffer. I received one comment regarding Epsom Salt not containing sodium. The term salt is used in chemistry, but not always in connection with sodium. An Epsom Salt injury is often equated to a chemical compound. As previously stated, Epsom Salt is a chemical compound.
Nitrogen-fixing bacteria are unable to colonize the roots of plants with excessive amounts of magnesium sulfate. Also, excessive magnesium in the soil can release aluminum and make it available to aquatic and terrestrial plants. If we consume these plants, it would pose a health risk to us.
The calcium content in the soil needs to be 10 times greater than the magnesium in order to prevent magnesium toxicity. Adding Epsom salt alone can contribute to the imbalance and create a toxic environment for the plants trying to grow.
It is a good thing that Epsom salt is highly soluble, so it won’t remain in the soil and build up. But is that a good thing? Just think about that for a minute. Despite being extremely soluble, what many seem not to consider is the fact that the excess ends up somewhere, most often as a pollutant or contaminant in the environment, especially in waterways.
Additions to magnesium in our soils are relatively infrequent (have a soil test done) so why potentially harm an environment that is already struggling?
Epsom Salt for houseplants
In pots, houseplants aren’t as lucky as our garden plants in that they tend to accumulate too much nutrients.
Adding more magnesium and sulfur to a balanced fertilizer with all the necessary macro and micro nutrients will only result in a build-up. Leaves and roots will be damaged.
Test it Yourself
There is no substantial research that supports the use of Epsom salts on plants, but thousands of people still repot plants with a pinch of Epsom salts, add Epsom salts to their watering mixture every month, or spray the mixture on their plants’ leaves. Try it if you like — just dissolve one tablespoon of Epsom salt in one gallon of water — and decide for yourself if it works.