in the Garden
If you know your soil is deficient in magnesium, adding Epsom salt can be a good idea. However, most soil will maintain plenty of magnesium, sulfur, and other nutrients if you regularly add compost each year.
Myth: Using Epsom salt helps seeds germinate.
The truth is that most seeds can germinate without essential elements. Seeds often can germinate with little more than moisture on a paper towel. Thus, the idea that you need Epsom salts to get seeds going is a myth.
Some sources suggest applying a foliar spray of 1 tablespoon of Epsom salts mixed with four cups of water for each foot of plant height. Magnesium absorbs well if it’s applied directly to the leaves. Be sure to dilute the spray and apply it on cooler or cloudier days.
Reports on which this is claim based are from more than 60 years ago and focused on intensive tomato production. The average home gardener does not need to put Epsom salts on tomato plants.
Myth: Epsom salts prevent blossom end rot.
Using Epsom salts to prevent blossom end rot in tomatoes is unfounded. Blossom end rot is a calcium deficiency and its cause usually has to do with watering problems, not low levels of calcium in the soil.
Epsom salts have been used to ease magnesium deficiencies found in turf or pastureland, since grazing can lessen the nutrient’s presence in the soil. It is a short-term solution, however.
Myth: Epsom salt plant food gives houseplants a boost.
Although Epsom salts are pH neutral and gentle on plants, they are not plant fertilizers. Eventually, the nutrients in potting soil all but disappear with time. So, in essence, Epsom salts on houseplants can replace some lost magnesium, but it's not a substitute for balanced houseplant fertilizer.
Some homeowners turn to a DIY means of removing a tree stump by enlisting Epsom salts to kill the remains of a cut tree first. Although it takes time to completely kill the stump, using a high quantity of Epsom salts dries up the root system (a warning for its use on live plants).
There is no evidence that Epsom salts boost flowering of roses or any other shrubs. The magnesium in Epsom salts can only supplement a slow-release rose fertilizer containing nitrogen, potassium, and phosphorus.
Myth: Spraying with Epsom salts can deter pests.
There is no scientific research to support claims of using Epsom salt for trees or other plants to deter pests and some diseases. In fact, spraying Epsom salts on foliage can cause leaf scorch.