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What Can Epsom Salts Do for Your Plants?

After working as a chemist at a biotechnology company, I enjoy writing about science, travel, and gardening.

Determine if your garden is deficient in magnesium and use Epsom salts to improve foliage, fruit quantity, and plant health.

Determine if your garden is deficient in magnesium and use Epsom salts to improve foliage, fruit quantity, and plant health.

I garden on a one-acre plot of land and have used Epsom salt to enhance my garden’s productivity and quality for several years. Inexpensive and easy to use, this natural salt is a wonderful fertilizer for lawns, flower beds, vegetable gardens, and potted plants. Unfortunately, it is also easy to overuse and may actually harm plants if an overage of magnesium is added to the garden soil.

In this article, you'll learn how to test whether your soil is magnesium deficient and how best to apply Epsom salt if it is. I'll also break down a few myths about using Epsom salt in the garden.

How to Use Magnesium Sulfate in Your Garden

Sandy, acidic, and clay soils are often deficient in magnesium. For regular use, add 1 tablespoon of Epsom salts to 1 gallon of water and use this solution to irrigate garden beds twice per month.

The most important step in using magnesium sulfate in your garden is to determine if your soil is actually deficient in magnesium. Buy a soil-testing kit online or check leaves for discoloration near the veins and leaf edges for a visual indicator of magnesium deficiency.

Certain types of leaf discoloration can indicate magnesium deficiency.

Certain types of leaf discoloration can indicate magnesium deficiency.

Support Photosynthesis and Add Color to Your Plants

Magnesium is the central element in the chlorophyll molecule and is absolutely required for plants to convert sunlight into energy for growth. Plants with yellowing or red/purple discoloration near leaf veins and edges are often deficient in magnesium. Adding Epsom salts to these plants will create lusher, greener foliage.

Yellowing lawns may be deficient in magnesium. Use Epsom salt for greener grass.

Yellowing lawns may be deficient in magnesium. Use Epsom salt for greener grass.

Help the Grass in Your Lawn Thrive

Magnesium deficiency can be observed by a yellowing of grass blades. A simple solution of 2 tablespoons of Epsom salt to 1 gallon of water will replenish the magnesium in the soil where the lawn is watered. 1 gallon of Epsom salt solution will treat approximately 1,000 square feet of lawn.

Magnesium is absorbed directly through the leaf structure, so it is not necessary to saturate the soil.

Add Nutrients to Your Fertilizer and Improve Absorption

Magnesium sulfate aids in the uptake of phosphorus, nitrogen, and sulfur. Water plants with a mixture of 1 tablespoon of Epsom salt to 1 gallon of water to enhance the uptake of these nutrients. Be careful not to overuse magnesium, as it competes with calcium and may lead to a deficiency of this nutrient.

Using the Epsom salt solution as a spray on plant leaves helps the plant absorb magnesium without adding it to the soil. This is an excellent way to prevent the salt from competing with calcium uptake in the plant.

Spraying and Epsom salt solution on plant leaves helps the plant absorb magnesium without adding it to the soil.

Spraying and Epsom salt solution on plant leaves helps the plant absorb magnesium without adding it to the soil.

Common Epsom Salt Gardening Myths

Many myths exist on the use of Epsom salt in the garden. In reality, the addition of magnesium sulfate will only help if the garden soil is actually deficient in magnesium. Most household garden soils are not deficient in this nutrient.

A testing kit can be purchased to test the soil, and if the soil is deficient, then magnesium sulfate will aid plant growth and vigor. If the soil is not deficient, adding more magnesium may be harmful to plants.

It Promotes Seed Germination

Several studies have demonstrated the use of Epsom salt actually decreases germination percentages. Take care in adding any salt or fertilizer to seeds, as many thrive in a nutrient-poor environment during the germination process.

The primary nutrients required by plants are potassium, oxygen, phosphorus, nitrogen, carbon, and hydrogen. Magnesium is actually a secondary nutrient that is used for photosynthesis and is a constituent of chlorophyll.

Nearly all seeds have sufficient stored nutrients to initiate root development and the growth of the first leaves. Most seeds will germinate by simply placing them on a wet paper towel, which has no nutrients at all!

It Prevents Blossom-End Rot

Epsom salt will create blossom-end rot, not prevent it. A lack of calcium in the plant’s system causes this defect in tomatoes, and magnesium ions compete with calcium ions in the plant’s uptake system.

Adding more magnesium will cause more magnesium to be taken up into the plant than calcium, potentially triggering a deficiency that will worsen rot in growing tomatoes.

Properly balance nutrients, including calcium and magnesium, to grow the best tomatoes.

Properly balance nutrients, including calcium and magnesium, to grow the best tomatoes.

It Improves the Flavor of Tomatoes and Other Fruits

It is vital to remember the improvement of tomato flavor will only occur if the soil is deficient in magnesium. An excess of magnesium may reduce fruit production and quality. Tomatoes may be firmer with the addition of magnesium and softer if the nutrient balance is shifted toward more calcium.

Applications of 300 mg/L calcium/50 mg/L magnesium near the end of the growing season improved the fruit quality of tomatoes in a study by the Journal of Canadian Plant Science. In this case, the amount of calcium added per liter was six times the amount of magnesium, resulting in optimal fruit growth. Balanced nutrients are required for crops, and gardeners should be careful not to add one nutrient in excess.

This tomato leaf demonstrates yellowing around the veins and is likely deficient in magnesium.

This tomato leaf demonstrates yellowing around the veins and is likely deficient in magnesium.

It Makes Tomatoes Grow Larger

Simply adding more magnesium to the soil will not increase tomato size. If the soil is deficient in magnesium, adding Epsom salts will increase fruit size and yield. If the soil has sufficient magnesium, adding more will actually decrease fruit size. For agricultural purposes, the amount of magnesium added to soil is measured as megagrams per hectare (Mg ha-1).

A study published in the Journal of Horticultural Science demonstrated tomato size was maximal with application at 50 kg Mg ha-1 and decreased at 75 kg Mg ha-1 to 100 kg Mg ha-1. If the soil is deficient in magnesium, adding Epsom salt will help. If the soil has sufficient magnesium, adding more may decrease fruit size and cause blossom-end rot.

It Boosts Flowering in Roses

As with tomatoes, the magnesium concentration in the soil matters. If the soil is deficient in this nutrient, adding magnesium will help a rose bush grow more canes and produce more flowers. If too much magnesium is added, calcium uptake will be inhibited in the rosebush. Symptoms of calcium deficiency include reduced petal formation and leaf deformation.

It Repels Slugs and Snails

While Epsom salt can kill slugs and snails on contact, it will not repel them from the garden. Some gardeners will place a ring of the salt around a plant they want to spare from slug damage. This is only temporarily effective as the slugs will exist elsewhere in the garden and will gain access to the plant as soon as rain or irrigation washes the salt away.

Epsom Salt FAQs

Magnesium sulfate is a salt that is used for many purposes around the home, including enriching garden soil. Many home gardeners have questions about the use of Epsom salt, including environmental impact and soil testing.

Where Can I Buy Epsom Salts for Gardening?

Epsom salts may be purchased at most grocery stores and are often located near the bath soap aisle (these salts are used to relieve muscle aches and pains). Be sure to purchase plain Epsom salt, not salt with essential oils added for scent.

Check leaves for discoloration near veins and edges to visually check for a magnesium deficiency.

Check leaves for discoloration near veins and edges to visually check for a magnesium deficiency.

How Can I Determine If Epsom Salts Will Help My Garden?

I have used the MySoil testing kit (available online) to test my garden soil prior to supplementing the ground with magnesium.

Using a testing kit will also determine if the soil’s potassium level is too high. If potassium is in excess, plants will not be able to take up sufficient magnesium levels and will exhibit signs of magnesium deficiency. In this case, however, adding more magnesium to the garden will not help. The level of potassium must be reduced to allow plants to use the magnesium already available in the soil.

A visual method to identify magnesium deficiency in plants is to check the plant’s leaves. Deficient plants will exhibit yellowing near the leaf veins and yellow or brown leaf edges. Purple or red discoloration may also be observed. Magnesium is required for photosynthesis, and older leaves will suffer the discoloration before younger plant leaves.

Leafy greens benefit the most from magnesium supplementation.

Leafy greens benefit the most from magnesium supplementation.

Which Plants Benefit Most From Epsom Salts?

Leafy green crops like kale, collard greens, and spinach require the most magnesium for growth. Adding Epsom salt to the soil will generally benefit these plants the most. Bean plants, corn, and wheat also require soil with sufficient magnesium or they will yellow and perform poorly in the garden.

Which Plants Don’t Like Epsom Salts?

Magnesium toxicity is extremely rare in any plant. In general, calcium or potassium deficiency is observed as the first indicator the magnesium concentration is too high in the soil. Tomatoes may suffer from blossom-end rot and other plants may exhibit chlorosis (whitening of the leaves) and develop brown spots from a calcium deficiency.

Spray an Epsom salt solution onto plant leaves rather than pour it into the topsoil, where it might leach into groundwater supplies.

Spray an Epsom salt solution onto plant leaves rather than pour it into the topsoil, where it might leach into groundwater supplies.

Are Epsom Salts Bad for the Environment?

Many sites state there are no negatives of using Epsom salt, as it is highly soluble and rarely leads to accumulation of magnesium in the soil. Unfortunately, its soluble nature means that applications in excess of what is needed for plant health will leach into groundwater, where it becomes a pollutant.

Citations

  1. G. W. Winsor, J. H. L. Messing & M. I. E. Long (1965) The Effects of Magnesium Deficiency on the Yield and Quality of Glasshouse Tomatoes Grown at Two Levels of Potassium, Journal of Horticultural Science, 40:2, 118-132, DOI: 10.1080/00221589.1965.11514126
  2. Kwon, M. C., Kim, Y. X., Lee, S., Jung, E. S., Singh, D., Sung, J., & Lee, C. H. (2019). Comparative Metabolomics Unravel the Effect of Magnesium Oversupply on Tomato Fruit Quality and Associated Plant Metabolism. Metabolites, 9(10), 231. https://doi.org/10.3390/metabo9100231
  3. Effect of Four Different Salts on Seed Germination and Morphological Characteristics of Oryza sativa L. cv. MR219. (2018). International Journal of Advanced Research in Botany, 4(1). https://doi.org/10.20431/2455-4316.0401005

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2021 Leah Lefler

Comments

Leah Lefler (author) from Western New York on June 27, 2021:

I am glad the article helped, Dora. Sandy and clay soils are particularly prone to nutrient deficiencies and plants often show poor growth in these conditions. We live in an area with a lot of clay and shale, so we occasionally have to apply fertilizer and magnesium supplementation to our garden.

Dora Weithers from The Caribbean on June 27, 2021:

Thanks for this very helpful article. I was ready to go out and start applying Epsom Salts because the leaves in your picture resemble some in my yard. Thanks for the warning, and for all the smart facts.

Leah Lefler (author) from Western New York on June 27, 2021:

Some gardeners overapply magnesium sulfate and actually cause damage to their plants. I really wanted to point out that Epsom salt only helps if the soil is lacking sufficient quantities of magnesium, Liz!

Leah Lefler (author) from Western New York on June 27, 2021:

It is an inexpensive way to boost plant health if there is a deficiency. I keep Epsom salt in our pantry because there are so many uses for it!

Liz Westwood from UK on June 26, 2021:

This is a fascinating article. I appreciate the way that you address some of the myths associated with Epsom salts and gardening.

Peggy Woods from Houston, Texas on June 26, 2021:

This article about the use of epsom salts in gardening is very informative. Thanks!

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