Epsom Salts and Plants – Is It Worth Using Epsom Salts as a Plant Fertilizer?

— Written By Brenda Larson and last updated by

Gardeners have been using Epsom salts as a plant fertilizer for generations, but is there any evidence there’s a real benefit to the plants? There is little research to prove conclusively that Epsom salts have any effect on plants, but 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. They were first discovered in Epsom, England, where they got their name. You can find cartons of Epsom salt in drug stores and groceries, either in the laxative aisle or the sore muscle section.

What are Epsom Salts Supposed to do for Plants?

Epsom salts contain hydrated magnesium sulfate, two elements crucial 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 top soil or a pH imbalance. Some plants, like lettuce and spinach, don’t mind going without magnesium. Others may exhibit symptoms like leaf curing, stunted growth, that could be attributed to more than one cause. Magnesium deficiency has even been blamed as a cause for bitter tomatoes. 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 Better?
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 are 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 are not going to 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 more lush, it produces more canes and more roses. The recommendation for applying to existing rose bushes, is to either mix ½ cup of Epsom salts into the soil around the rose bush and water well or dissolve ½ cup of the salts in water and use to water the rose bush. Do this in the spring, just as the bids are beginning to open.

For ongoing rose care, mix 1 tbsp 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 use and do not spray on hot, sunny days.

  • Epsom Salts for Tomatoes and Peppers

Tomatoes and peppers may show signs of magnesium deficiency late in the season, when their leaves begin to yellow between the leaf veins and fruit production decreases. Whether you will get more and/or larger fruits will depend on many things besides applying Epsom salts, but using them before the plants start to decline, does seem to have some benefit.

Either mix in 1 tbsp of Epsom salts into the soil at the bottom of the planting hole when setting out transplants or mix the 1 tbsp in a gallon of water and water the seedling.

Follow-up with a foliar spray of 1 tbsp per gallon of water when the plants start to flower and again when the young fruits start to form. Try 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. In this case I’d recommend a more dilute solution, mixing only 1 tsp 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 some gardeners simply use the Epsom salts when they remember.

Brenda Larson is Horticulture Agent for North Carolina Cooperative Extension in Lee County.

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