Q: I have heard that Epsom salt can do everything from jumpstarting tomatoes to fertilizing garden shrubs. How do I know when to use Epsom salts for plants, and how to separate fact from fiction?
A: Epsom salt has a place in the garden, but a more limited one than social media posts might have you believe. Epsom salt contains relatively high levels of magnesium and sulfur. Although these are essential elements plants need, they are among many that contribute to growth and flowering or fruiting. Both elements aid in photosynthesis and help plants absorb the three macronutrients (nitrogen, phosphorus, and potassium). But plants don’t need magnesium and sulfur in large amounts; most soils provide them without additives.
In large crop-growing or timber-harvesting operations around the world, magnesium deficiencies can occur. Farmers have used Epsom salts to add magnesium for intensive crop or conifer production when the soil lacks magnesium. The causes of nutrient deficiencies are complex, and depend largely on the makeup of the soil, other mineral imbalances, and even the amount of rainfall or irrigation the crops receive.
Let’s take a look at ways in which the average home garden might require Epsom salt, as well as some of the myths or overstatements of its plant-supporting powers.
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Fact: Use of Epsom salt can boost a soil’s magnesium levels.
If you know your soil is deficient in magnesium, adding Epsom salt to your garden soil can be a good idea. However, most soil (especially loamy soil) will maintain plenty of magnesium, sulfur, and other nutrients if you regularly add some compost each year.
If your soil is sandy or really acidic (with a pH level below 6.0), it is more likely that it has a magnesium deficiency. The only way to truly know that is to do a soil test. Check with your county extension office to learn about soil makeup in your area and to find soil testing resources before adding Epsom salts, garden lime, or other amendments. If soil lacks magnesium, use Epsom salt to boost it, but don’t expect it to be the end-all solution for low magnesium or other elements in soil.
Myth: Using Epsom salt for gardening improves nutrient absorption, seed germination, and healthy plant starts.
There is a popular belief that the magnesium in the salts boosts seed germination by strengthening cell walls and providing increased energy for growth. It is said that applying a drench of 1 tablespoon of Epsom salts for every gallon of water to the soil after seeding helps keep sulfur levels up. You may also have read that adding a tablespoon of Epsom salts into a hole before planting a seed, or sprinkling a seeded bed with a cup of Epsom salts, benefits plants.
The truth is that most seeds can germinate without essential elements, especially those that are planted in seed starting mixes, which are designed for that purpose. Seeds often can germinate with little more than moisture on a paper towel. Thus, the idea that you need Epsom salts to get seeds going is a myth.
Tests have indicated that magnesium sulfate can increase cell uptake of key minerals, including nitrogen and phosphorus. Testers in five states gave pepper plants a standard drench of 1 tablespoon Epsom salts to one gallon of water, twice a month, and reported that many of the treated plants showed thicker foliage and larger vegetables.
New and transplanted roots need tender care. The magnesium might help new seedlings get a good start, but adding it really isn’t necessary if you’re starting with quality garden soil and potting mixes. On the other hand, using some Epsom salt for gardening likely won’t harm plants or soil unless it’s applied often and too heavily.
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Fact: Epsom salt in the garden can turn yellowing leaves green.
Mineral deficiencies can interfere with photosynthesis, leaching green color from leaves and interfering with nutrient absorption. If more mature foliage is turning yellow between the veins, this may indicate a magnesium deficiency. Yellowing leaves all over a plant might indicate a sulfur deficiency.
Some sources suggest applying a foliar spray of 1 tablespoon of Epsom salts mixed with four cups of water for each foot of plant height. Magnesium absorbs well if it’s applied directly to the leaves. Be sure to dilute the spray as described above and apply it on cooler or cloudier days.
Myth: Epsom salts on tomato plants, peppers, and other veggies will increase yield and enhance flavor.
Many sources suggest that every month during the growing season, gardeners should mix 1 tablespoon of Epsom salts to each gallon of water and apply liberally to the roots of fruit and nut trees, grapevines, and berry patches. Another technique is to apply 2 tablespoons of dry Epsom salts over a 9-foot root-bed area, three times a year.
Sweet peppers and tomatoes are said to benefit if gardeners add 2 tablespoons of Epsom salt to the soil of each hole at planting time, and apply a foliar spray (made up of 2 tablespoons of salt to each gallon of water) once a month.
In truth, reports on which this is claim based are from more than 60 years ago and focused on intensive tomato production. The average home gardener does not need to put Epsom salts on tomato plants. Overusing the product could contaminate the soil or harm plants.
Myth: Epsom salts can prevent blossom end rot in tomatoes.
Mentions of Epsom salts to prevent blossom end rot in tomatoes are unfounded; it’s not even clear how this myth started. In reality, blossom end rot is a calcium deficiency and its cause usually has to do with watering problems, not low levels of calcium in the soil. In fact, adding too much magnesium to soil might compete with the calcium as a nutrient, making matters worse.
Tomatoes need consistent moisture, and do poorly if they dry out one day and then you drench them another day. Use a soaker hose or other slow drip method you can put on a timer to water tomatoes consistently, mulch the soil around the roots, and leave the Epsom salts in the cupboard.
Fact: Spread or spray Epsom salt fertilizer on your lawn to help it grow.
Epsom salt is not a fertilizer or plant food. It contains some elements that plants need, but not all of them. Epsom salts have been used to ease magnesium deficiencies found in turf or pastureland, since grazing can lessen the nutrient’s presence in the soil. It is a short-term solution, however. Plus, the magnesium in Epsom salt is highly soluble and can leach or run off into water supplies, contributing to water pollution and escaping the soil it’s meant to improve.
If your soil tests positive for magnesium deficiency, Epsom salts might help your lawn with some growth and lushness. The Epsom Salt Council recommends applying 3 pounds of salts for every 1,250 square feet of lawn with a spreader or diluted with water from a hose or sprinkler system. Consider this a quick fix for turf, not a long-term management strategy.
Myth: Epsom salt plant food gives houseplants a boost.
Although Epsom salts are pH neutral and gentle on plants, including spotted houseplants, they are not plant fertilizers. The soil in houseplant containers can become depleted of most essential nutrients. Watering leaches out some, and unlike garden soil in the ground, the potting mix does not process microbes and organic matter. Eventually, the nutrients in potting soil all but disappear with time. So, in essence, Epsom salts on houseplants can replace some lost magnesium.
You might have heard that you can boost nutrient intake by mixing 2 tablespoons of Epsom salts with one gallon of water and spraying it onto leaves for maximum absorption. Alternatively, some sources suggest adding the salts directly to the soil: 1 teaspoon of salts for every foot of plant height. Some bloggers suggest adding Epsom salts to your houseplants every month, monitoring subtle changes in leaf vibrancy and growth.
The truth is that houseplants benefit much more from regular application of a balanced organic >fertilizer to restore soil health. Many houseplants also grow best if repotted every few years, both to support root growth and replace depleted soil with nutrient-rich mixes.
Mostly fact: Remove tree stumps more easily by drying them out with bulk Epsom salt.
Some homeowners turn to a DIY means of removing a tree stump by enlisting Epsom salts to kill the remains of a cut tree first. Although it takes time to completely kill the stump, using a high quantity of Epsom salts dries up the root system (a warning for its use on live plants).
When you consider that professional stump removal services can cost between $160 and $500 or so, depending on the size of the trunk, this one might be worth a try, especially since some tree care companies mention this technique as a DIY stump removal method.
Bore holes all around the top of the stump with a drill, using a ½-inch drill bit; these holes should be about half the depth of the stump and spaced a few inches apart. Then, pour dry Epsom salts into the holes and slowly add water to moisten, but not saturate, the salts. Cover the stump with a tarp to repel rain and ensure the drying process.
You might have to repeat it several times, but use of Epsom salts should speed up the wood’s drying, which makes it easier to chip away at the stump with an ax and eventually dig up and dispose of the remaining root system. So, this is not a quick fix, but an inexpensive DIY alternative to stump removal service.
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Mostly Myth: Use Epsom salt for roses for improved flower production.
Plenty of myths abound about use of Epsom salt for flowering plants, including roses. They include adding a tablespoon of salts for every gallon of water and spraying foliage when established plants begin to leaf in spring, and once again during flowering. Instructions also say to add 1 tablespoon of Epsom salts to the bottom of each hole before planting a new rose bush.
However, there is no evidence that Epsom salts boost flowering of roses or any other shrubs. The magnesium in Epsom salts can only supplement a slow-release rose fertilizer containing nitrogen, potassium, and phosphorus.
Myth: Spraying with Epsom salts can deter pests.
There is no scientific research to support claims of using Epsom salt for trees or other plants to deter pests and some diseases.
In fact, spraying Epsom salts on foliage can cause leaf scorch. Damaged leaves do not recover from scorching. The good news is that scorched edges of leaves does not prevent photosynthesis, and scorched edges are really more of a problem on ornamental plants because it affects foliage appearance. If you do spray the salt on leaves, be sure it is heavily diluted with water and avoid spraying it on hot sunny days.
Myth: Epsom salts do not build up in soil and therefore you cannot harm plants or soil.
Although it is true that Epsom salts are highly soluble, any nutrient used in excess or where it’s not needed can persist in soil and compete with other nutrients that plant roots take up and distribute within a plant. That’s especially true with potted plants, since too much Epsom salt in the soil has nowhere to go.
A concern with Epsom salts is that although they might not last a long time where they’re applied, they will go somewhere. They’ll wash away with water that runs off and become a pollutant that contaminates waterways. So, avoid using too much Epsom salt or any soil additive or fertilizer to do the least harm to plants and the environment. Instead, keep plants consistently watered and soil rich in nutrients with annual additions of organic compost.