What are Epsom Salts?
Epsom salt, also known as magnesium sulfate, is a naturally occurring mineral compound comprised of magnesium, sulfur, and oxygen.
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It takes its common name from the place where it was first discovered—the waters near the town of Epsom, in Surrey, England—and was likely called a “salt” due to its crystalline chemical structure. Over the centuries, people have employed Epsom salts as a laxative and as a soothing soak for sore muscles, so it’s typically found in drugstores, not nurseries. Yet gardeners have been using Epsom salts as a fertilizer for many years.
Why are Epsom Salts Believed to Benefit Plants?
Both sulfur and magnesium are secondary nutrients key to plant growth. Sulfur aids chlorophyll formation, assists in nitrogen use, and makes plants more disease resistant. Magnesium enhances plants’ cellular structure, helping them to better absorb other nutrients, notably phosphorus. Epsom salts proponents contend that magnesium can also boost photosynthesis, germination, and seed formation.
Is it Important to Add these Nutrients?
While most soil tends to have adequate sulfur, some may be magnesium deficient, especially sandy and/or acid soil. Magnesium can also be leached by heavy rainfall, irrigation, erosion, and extensive cultivation. So replenishing magnesium with Epsom salts certainly sounds like a good idea. And those on Team Epsom point to their abundant blooms and bumper crops (particularly of roses, tomatoes, and peppers) as evidence that magnesium sulfate works wonders. Unfortunately, there’s scant research to back up the anecdotal evidence, and those in the anti-Epsom camp point out that sulfur and magnesium are mere minor players in the scheme of plant health.
Is a Soil Test Necessary?
Generally speaking, it’s wise to understand what’s going on with your soil before using fertilizer or amendments. For example, plants may show signs of magnesium deficiency, but excess potassium in the soil may be prohibiting magnesium intake—a condition that may be best addressed by adding nitrogen. Purchase a DIY soil test kit or send a sample to a local department of conservation or college agriculture department to determine what nutrients your soil is lacking and how to treat it.
Are There Visible Signs that Epsom Salts Improve Plants?
Different nutrient deficiencies often have similar symptoms, so a soil test is typically the best start to diagnosing a problem. That said, yellowing leaves all over a plant may indicate a sulfur deficiency. Lower leaves that turn yellow between the veins while the veins themselves remain green may be a sign of magnesium deficiency.
How Epsom Salts are Used in the Garden
Consider these formulas and methods that Epsom salts advocates routinely rely on. For general garden start-up, mix one cup of Epsom salts per 100 square feet into soil before planting. To boost germination, mix one tablespoon of Epsom salts in a gallon of water and add to soil after seeding. To aid nutrient intake, dissolve one tablespoon of Epsom salts in a gallon of water and use as a foliar spray twice monthly. For a lush lawn, lightly sprinkle three pounds of Epsom salts for every 1,250 square feet of turf and water well. To encourage abundant roses and bright foliage, apply one-half cup of Epsom salts to the soil around the base of each bush. Perform the treatment early in the blooming season, when buds are just beginning to open, for best results. For such shrubs as azaleas and rhododendron, sprinkle about a tablespoon of Epsom salts at the root zone (where roots spread out past the drip line, the ring-like area around the base of the plant) every two to four weeks. To give tomatoes and peppers a healthy start, add a tablespoon of Epsom salts to the bottom of each hole prior to transplanting seedlings. Once tomato plants flower and begin to fruit, mix a foliar spray of one tablespoon of Epsom salts to a gallon of water and spray weekly. To banish slugs and snails, sprinkle Epsom salts around the base of plants.
Risks to Using Epsom Salts in the Garden
There are two specific cautions when it comes to Epsom salts—and one larger concern.
If applied directly onto foliage, Epsom salts can cause leaf scorch. Use a wetting agent and avoid spraying on particularly hot, sunny days to mitigate this. Calcium deficiency can cause root rot, common in tomatoes. Epsom salt may worsen the situation because calcium and magnesium compete with each other for absorption by the plant.
Beyond those issues is the fact that Epsom salts are highly soluble. So while fans think that’s great, extolling “you can’t use too much of it,” foes note that when excess washes away, it will wind up someplace—as a pollutant.
The Bottom Line on Epsom Salts in the Garden
Perhaps you’ll end up as a rapturous Epsom salts extoller, a diehard decrier, or somewhere in between.
