Epsom Salts & Plants

Epsom salt is nothing more than hydrated magnesium sulfate. Organic farmers tout Epsom salts as a natural way to offer highly absorbable magnesium to your plants. However, using Epsom salts on plants and gardens is a controversial subject.

Epsom Salts on Houseplants

Not all houseplant fertilizers provide enough magnesium in all situations. If you find your plants have developed yellow or white margins, magnesium deficiency may be the cause. In the case of houseplants, supplemental feeding with a small amount of Epsom salt might solve the problem. It would be cost-prohibitive to test each of your houseplants for soil conditions. Instead, add 1 tsp. of Epsom salts to a gallon of water and water your plants normally. If there is no improvement in one month's time, or anytime your plants worsen, discontinue the Epsom salt treatment and try something else. This kind of deficiency often occurs when using distilled water on houseplants.

Epsom Salts on Roses

The Epsom Salt Council recommends heavy use of Epsom salt on roses. They recommend applying 1 tbsp. every two weeks, spraying a dilute solution of Epsom salt on the rose bush weekly and adding 1/2 cup of Epsom salt to a newly dug hole. However, a controlled study showed Epsom salt didn't protect the plant against black spot and had a negative effect on the roses' flowering and growth. Plants treated with Epsom salt did retain more leaves. Other ways of treating back spot include fungicides and the removal of shed leaves to reduce the amount of fungus in the soil.

Soil Testing

Test garden soils before applying Epsom salts intended to alter the mineral composition of the soil. Most land grant universities offer soil testing through their extension services. Applying Epsom salts or other fertilizers without testing the soil can result in an unwanted pH change. Changing the pH of the soil also affects the soil bacteria. To test your soil, take samples from four to six holes per garden area. This doesn't mean to sample each garden bed, but if you have different types of gardens, perennial vs. annual for instance, sample each garden separately.

When Not to Use Epsom Salts

If your soil tests come back stating that your soil has enough magnesium, don't apply Epsom salt. One of the selling points of Epsom salt is also a drawback, especially if you are fertilizing a large area or are in a concentrated urban environment. Epsom salt is immediately available to the plants and soil because it is soluble. However, this means that any excess Epsom salt washes away with the next rainfall. Excess fertilizer runoff isn't good for the rivers and lakes and can lead to unwanted weed growth. It's best to fertilize just the right amount and only where it's needed.

References

• North Dakota State University; Questions on: Houseplant Foliage; Ron Smith
• Epsom Salt Council: Garden Usage Tips
• Auburn; "Management Key to Controlling Blackspot Disease in Roses"; Kira L. Bowen, Bridget K. Behe, and Elizabeth A. Guertal; 1996
• North Carolina Dept. of Agriculture and Consumer Services: Soil Testing
• Puyallup University; "Adding Epsom Salts to gardens is a safe, natural way to increase Plant Growth"; Linda Chalker-Scott, Ph.D.

Resources

• University of Florida: "Nutrient Deficiency Symptoms of Woody Plants"; Timothy Broschat; 2009