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Horticulture Experts Explain When & How To Use Epsom Salt On Plants

Author:

Emma Loewe

January 22, 2021

By Emma Loewe

mbg Contributor

Emma Loewe is the former Sustainability and Health Director at mindbodygreen. She is the author of "Return to Nature: The New Science of How Natural Landscapes Restore Us" and the co-author of "The Spirit Almanac: A Modern Guide To Ancient Self Care." Emma received her B.A. in Environmental Science & Policy with a specialty in environmental communications from Duke University. In addition to penning over 1,500 mbg articles on topics from the water crisis in California to the rise of urban beekeeping, her work has appeared on Grist, Bloomberg News, Bustle, and Forbes.

January 22, 2021

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You probably already associate Epsom salts with bathtime: Adding a scoop to your tub can help relax tight muscles, ease anxiety, and soothe the skin. And some gardeners say that this type of salt—a combination of magnesium and sulfur—can be great for soaking your plant pals, too.

The science is there for the human benefits of Epsom salts, but the plant ones? We asked some horticulture experts to get the scoop.

The logic behind using Epsom salts on plants.

Plants, like people, need magnesium to function. "Magnesium is one of the essential macronutrients a plant needs to photosynthesize," Summer Rayne Oakes, the plant authority behind Plant One on Me, tells mbg. "If you go back to biology days, you may recall that Mg is the central ion in chlorophyll, so plants need it to make food. It's also needed in RNA and DNA synthesis, binds with lots of important enzymes, and assimilates phosphorus, which is another vital macronutrient." The sulfur in Epsom salt is also beneficial, helping plants form important enzymes and proteins.

The healthiest and most resilient plants are the ones that are getting just the right amount of all the essential nutrients—from magnesium and sulfur to nitrogen, phosphorous, and potassium. That's why it's important to fertilize plants regularly, especially if their soil has any known deficiencies.

Epsom salt is not a complete fertilizer, so while it can boost the magnesium and sulfur count in soil, it won't add any of those other nutrients a plant needs to grow strong.

So, like coffee grounds, the value of Epsom salt as a garden additive has been slightly exaggerated. Unless your soil is deficient in magnesium and sulfur, certified professional horticulturist and author Leslie F. Halleck, M.S., says that the salts won't do all that much. "And if you already have quite a bit of available magnesium in the soil," Oakes adds, "then it can cause complications for the uptake of other nutrients."

How to know if your plants could use it.

That being said, a small group of curious gardeners has tracked their experience using Epsom salts on plants and reported some success to the National Gardening Association. For soil with slightly low magnesium levels, a salty bath did seem to boost plant growth, flowering, and fruiting for roses, tomatoes, and peppers.

However, the cohort of six gardeners noted that "it's hard to find a direct link between a specific nutrient such as magnesium sulfate and increased yield or plant growth because of all the other variables in the soil, such as pH, calcium, and potassium content, and weather, that may affect the plants."

If you're curious enough to give Epsom salts a try on your plants (they are, after all, really cheap and easy to use), here's how to tell if your greenery could use the extra nutrients:

Outdoor plants:

Before applying Epsom salts in the garden, Halleck says, "It's always a good idea to have a soil test performed on your native garden soil or soil in your raised beds." Doing so will help you decide which nutrients may require supplementation. "If your soil test shows you need more magnesium or sulfur, or both, then Epsom salts may be a good addition to your fertilizer regimen."

Indoor plants:

Getting the soil of every indoor potted plant professionally tested isn't worth the hassle. When deciding whether your indoor plants could use some Epsom salts, just look out for a visual sign of magnesium deficiency. Oakes says the most obvious one is splotchy yellowing between leaf veins, called interveinal chlorosis.

How to apply it.

Add 1 to 2 tablespoons of Epsom salts to a gallon of warm water, and shake to combine. (That National Gardening Association study concluded that a ratio higher than that won't be any more effective.) If you're working with houseplants, stick to the lower end of that range.
Once every few months during growing season, use this slightly salinated mixture on your plants instead of water. You can either apply directly to the soil or spray the mixture onto your plants' leaves for faster absorption.
Use a steady hand. "The amount of magnesium a plant needs is fairly minute, so it's also very easy to overdo it and 'overfertilize' plants," Oakes warns. Signs that you've overdone it include stunted growth and darker leaves.

Summary

Epsom salt is a popular DIY fertilizer for outdoor and indoor plants. And while it has been shown to boost the magnesium and sulfur content of soil, horticulture experts say it should only be used on plants with known deficiencies in those nutrients.