A handful of plain Epsom salt, magnesium sulfate.
Julia Nichols ©2025 HGIC, Clemson Extension
With the growing season quickly approaching, you will soon be inundated with information on how to fertilize your garden with household items. Epsom salt is typically marketed as an organic way to feed your plants the necessary magnesium they may need. It has been touted as a natural way to improve blossom end rot and increase crop yields; however, scientific research suggests otherwise.
The Role of Magnesium in Plants
Magnesium (Mg) is considered a micronutrient for plants, meaning plants only need it in minimal quantities. Plants use magnesium in carbohydrate transportation, photosynthesis, and the synthesis of proteins. Mg levels in most garden spaces, especially if amended with organic matter, are generally already at sufficient levels for plants. While Epsom salt does contain magnesium sulfate, it can also add unnecessary salt to your garden soil if used in excess.
Use a Soil Test to Determine Magnesium Levels
The first step to checking your soil’s nutrient levels is completing a soil test by an accredited soil or agricultural laboratory in your state. Soil testing is the most accurate way to let you know where your magnesium levels stand, and the results will contain fertilizing recommendations if adjustments are needed. University-run Extension Services have their own soil testing laboratories. At-home soil test kits can result in inaccurate or inconsistent results. Contact your local county Extension office to inquire about a soil test. For soil testing and fee information for South Carolina residents, see Clemson Ag Service Lab: Soil Testing.
Is it Possible to Apply Too Much Epsom Salt?
Too much salt in the soil can create a saline environment that garden and vegetable plants do not enjoy. Magnesium sulfate (MgSO4) is a magnesium salt. Salt can begin accumulating around each plant’s root zone, blocking the plant’s ability to take up water from the surrounding soil. If soil magnesium levels are already sufficient, too much magnesium inhibits calcium uptake. The more magnesium in the soil, the less likely calcium will be absorbed and can worsen blossom end rot on tomatoes, peppers, and eggplant. The plant will then display general symptoms of an excess of salts. This can include dark-colored vegetation and stunted overall growth.
Alternatives to Using Epsom Salt
It is good practice to refresh your garden soil with organic matter before Spring or Fall plantings each year. Organic composts, properly aged manures, crop residue, and mulches (tree leaves, grass clippings, or straw) are all good choices for adding organic material. Organic matter improves depleted nutrient levels, improves drainage, and helps to aerate the soil properly. With Mg only being needed in plants at minuscule levels, adding organic materials to your garden will add sufficient amounts of Mg and other micronutrients. For more information on organic matter, see The Role of Organic Matter in Healthy Soils.
Can Applying Water Help Reduce Salt Levels in the Garden?
If Epsom salts have been used in your garden and you are worried about salt levels, flushing your garden space with water can help dissolve these salts and carry them away. This practice is known as leaching. Flushing the area a few times before planting plants can help desalinize the growing space. A soil test measuring soluble salts can give you an exact idea of the amount of salt in your growing space and tell you where your natural range should be.
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