Every spring, articles and social media posts on using Epsom Salts to improve your garden and lawn are ubiquitous. You’re encouraged to use Epsom Salts for bigger blooms, better shrubs, greener grass and even pest control. The truth is, there are no scientific studies – none – to back up the claims about Epsom Salts and for the most part these are at best, urban myths.
The claims for Epsom salts include:
- fertilizer for lawn and garden
- speed seed germination
- makes shrubs “bushier”
The facts about Epsom Salts
Epsom Salts are not actually a salt and are not related to table salt in any way. Table salt is sodium chloride; Epsom Salts are sulfate (sulfur+oxygen) and magnesium. The Epsom refers to the area of England in which the salts were first collected from a spring.
Most articles and posts claim that adding Epsom Salts to soil and around roots when planting tomatoes, peppers and other vegetables, boosts magnesium and sulfur levels, which stimulates blooms. But few soils are deficient in magnesium or sulfur except for very sandy soils which experience a great deal of rainfall. And with any fertilizer, more is not better – each plant requires specific amounts of nitrogen, potassium, phosphorous, magnesium, calcium, sulfur and other elements, and what they don’t take up washes away as a pollutant. A lack of magnesium uptake by plants is usually caused by excessive potassium in the soil and adding more magnesium won’t improve the situation at all. Magnesium and sulfur are micronutrients from a plant’s perspective – they need only small amounts for optimum health.
But Epsom Salts are sometimes used in commercial agriculture (crops under intensive cultivation, unlike your garden) when the soil has been shown to be deficient in Magnesium (based on soil tests).
It’s also promoted to discourage Blossom End Rot in tomatoes. But Blossom End Rot is caused by a lack of calcium and wet conditions. Magnesium actually competes with calcium for uptake, so adding Epsom Salts could make this problem much worse.
Epsom Salts are frequently advertised as highly soluble so they can’t be overused, which is false. Highly soluble chemicals which aren’t used by plants don’t just disappear from the environment – they wash away, to somewhere else, like your local waterways or neighboring properties.
Regarding the pesticidal claims, in scientific testing, insecticidal claims do not hold up. Epsom Salts are found to be of no value in killing insects, including slugs, at any stage in their development. A similar lack of results has been found in claims that epsom salts can reduce powdery mildew and apple scab.
As far as the claim that it helps seeds germinate: seeds already have all they need to germinate and require no fertilizer to do so. If you start seeds in a quality starting soil with a heat mat and proper amount of moisture, the seeds will germinate just fine.
Claims that Epsom Salts improve the health of shrubs and trees have not been reproduced and verified in any studies. Used as a foliar spray, Epsom Salts solution may actually cause leaf scorch.
On lawns, the use of epsom salts is discouraged, because grass doesn’t require magnesium. Epsom Salts are sometimes used to reinvigorate pasture land (once again, a crop under heavy cultivation). But it is only a temporary solution, as literally half of the chemicals was away when it rains.
The bottom line on Epsom Salts
Few soils are deficient in Magnesium or Sulfur and plants will only use as much of these nutrients as they require. The only way to know for sure if your soil is lacking in any element is to have it tested by an accredited soil lab. If your test results note a deficiency, you should only add the element/s needed and in proper quantities to bring the soil into the normal range.
Read more about busting the Epsom Salts myth from Linda Chalker- Scott, Ph.D.