ASK THE HORT AGENT
Question Can I add Epsom salt to my flowering plants?
Answer Yes you can, but why would you want to do that? A very wise man (Tom Glasgow) once told me “A person needs to have a reason for doing something before they do it.” That wise man was correct.
I am sure that the “reason” is to “make the flowers grow better.” The addition of Epsom salt may or may not make the flowers grow better. Epsom salt is high in magnesium (Mg). If you have a sandy soil, then your soil may need Mg. However, if your soil is low in Mg, then it is probably low in Calcium (Ca) and potassium (K) as well. Dolomitic lime, simply referred to as “lime”, contains both Ca and Mg.
But how do you know if you need Ca, K or Mg? Simply take a soil test. Cooperative Extension, high school horticulture instructors, local garden centers, and many others have all preached on the importance of taking soil samples. Farmers take soil samples, because they know how important it is to be efficient.
Soil sample results will indicate whether you need Mg, Ca, K or any other specific nutrient. These results will also tell you how to add that nutrient and how much to add.
There are times when you may need Mg, but do not need to raise the soil pH (lime will raise the pH). In these situations, then you can add Epsom salt at a general rate of one teaspoon per gallon of water.
If you need Mg and potassium, then you can add a fertilizer called Sul-Po-Mag (0-0-22). Again, the soil test results will tell you how much to add. The percent Mg in Sul-Po-Mg is about the same as the percent Mg in Epsom salt. Keep in mind that Epsom salt is not sold as a fertilizer. Therefore, it does not have to be as consistent with its analysis requirements as fertilizers.
More is not always better. Too much Mg in the soil can hinder a plant's ability to take up Ca and K. Be careful when you are listening to the advice of a neighbor that is “spreading it on too thick.”
When in doubt, find out. Take a soil sample, and take the guess work out of the process. In North Carolina, soil samples are analyzed by the North Carolina Department of Agriculture. Their lab is located in Raleigh near the fairgrounds. You can find sampling information at http://www.ncagr.com/agronomi/pubs.htm You can also call me at 910-893-7533 or email me at firstname.lastname@example.org
Epsom salt is great for soaking your feet or your whole body. It can be used for other medical purposes as well. I’m sure you would consult your doctor, not your neighbor when using Epsom salt as a laxative.
Gary L. Pierce
Horticulture Extension AgentHarnett County