Gardeners have been using Epsom salts as a plant fertilizer or soil additive for generations, but is there any evidence there's a real benefit ? Very little research has proven conclusively that Epsom salts have any effect on plants. There's little research done in general on homemade gardening fertilizers and pest controls. However, many seasoned gardeners cite their own gardens as proof that Epsom salts help certain plants grow stronger and produce better.
What Are Epsom Salts?
Epsom salts are a naturally occurring mineral, magnesium sulfate. It was first discovered in Epsom, England, its namesake. You can find cartons and packages of Epsom salt sold in drug stores and groceries, either in the laxative aisle, the sore muscle section, or the bath section; Epsom salts have many uses.
What Are Epsom Salts Supposed to Do for Plants?
Epsom salts contain hydrated magnesium sulfate, two elements central to plant growth.
- Sulfur (13%) is crucial to the inner workings of plants, but it is almost never lacking in the soil thanks in part to synthetic fertilizers and acid rain.
- Magnesium (10%) can become scarce in soil usually because of erosion or depletion of the topsoil or a pH imbalance. Some plants, like lettuce and spinach, don’t mind going without magnesium. Others might exhibit symptoms such as leaf curling and stunted growth, although these symptoms could be attributed to more than one cause. Magnesium deficiency has even been blamed as a cause for bitter tomatoes, probably because the deficiency inhibits photosynthesis. However, according to the extension service at the University of Minnesota, unless your soil has been tested and results reveal a magnesium deficiency, there is no need to add Epsom salts to your garden soil. Doing so could even be harmful to soil, plants and water.
In general, magnesium plays a role in strengthening the plant cell walls, allowing the plant to take in the nutrients it needs. It also aids in seed germination, photosynthesis, and in the formation of fruits and seeds.
Do Epsom Salts Really Help Plants Grow?
Researchers have never been terribly impressed with the effects of Epsom salts on plants and some think it is wrong to continue encouraging it. Gardeners tell a different story and the use of Epsom salts is a gardening tip passed down for generations. While many gardeners simply toss in a handful of Epsom salts at planting time, it really is wiser to test your soil first.
Epsom salts won't cure an extreme magnesium deficiency and are generally considered more effective in acid soils, where magnesium is not easily accessed by plants. Three garden plants for which Epsom salts are most often recommended are tomatoes, peppers, and roses.
Epsom Salt for Roses
Rose growers in particular are strong advocates for using Epsom salts. They claim it not only makes the foliage greener and lusher, but it also produces more canes and more roses. The recommendation for applying Epsom salt to existing rose bushes is to either mix 1/2 cup of Epsom salts into the soil around the rose bush and water well or dissolve 1/2 cup of the salts in water and use the solution to water the soil around the rose bush. Do this in the spring, just as the buds are beginning to open.
For ongoing rose care, mix one tablespoon of Epsom salts per gallon of water and apply as a foliar spray. You may need several gallons of water for larger rose bushes and climbers.
A word of caution: Epsom salts sprayed on leaves can cause leaf scorch. Do not over apply and do not spray on hot, sunny days.
Epsom Salts for Tomatoes and Peppers
Tomatoes and peppers might show signs of magnesium deficiency late in the season when their leaves begin to yellow between the leaf veins and fruit production decreases. Whether your plants produce more and/or larger fruits will depend on many things besides applying Epsom salts, but using it before the plants start to decline does seem to have some benefit.
Either mix in one tablespoon of Epsom salts into the soil at the bottom of the planting hole when setting out transplants or mix one tablespoon in a gallon of water and water the seedling.
Follow up with a foliar spray of one tablespoon per gallon of water when the plants start to flower and again when the young fruits start to form. Test it on a few plants and see if you can tell the difference as the season goes along.
This is a home gardening remedy and there are as many formulas for application as there are home gardens. Some gardeners only add Epsom salts at planting time. Others like to water or foliar feed with Epsom salts every other week. When spraying directly on the leaves, use a more dilute solution, mixing only one teaspoon of salts per gallon of water, because it is not known for sure whether excess salts will build up in the soil or run off into the water supply. And finally, some gardeners simply use the Epsom salts when they remember to do so.
“Coffee Grounds, Eggshells and Epsom Salts in the Home Garden.” Umn.Edu, https://extension.umn.edu/manage-soil-nutrients/coffee-grounds-eggshells-epsom-salts
Bromley, Barbara J. “NUTRIENT DEFICIENCY SYMPTOMS.” Mgofmc.Org, https://mgofmc.org/docs/nutrientdeficiency.pdf