Magnesium Sulfate for Plant Care

Magnesium Sulfate Characteristics

• Magnesium sulfate is a white, crystalline solid, similar in appearance to table salt. The name originates from the English town of Epsom and Ewell, an area known for its mineral springs, many of which contained Epsom salts. It is widely used in agriculture to correct magnesium deficiencies in soils, in liquid and granular form. It occurs naturally in soil, although it is susceptible to leeching from irrigation or rainfall.

Role in Plant Nutrition

• Magnesium sulfate supplies both magnesium and sulfur to growing plants, both of which are important nutrients. Magnesium forms the center of the chlorophyll molecule, an essential compound in the process of photosynthesis. Shortages of magnesium thus result in shortages of chlorophyll, which inhibits photosynthesis and results in stunted plant growth. Sulfur is a component of many plant amino acids and proteins, and plants utilize it for protein synthesis in its sulfate form. Yellowing leaves indicate sulfur deficiencies.

Application Rates

• Apply magnesium sulfate at a rate of 1 cup per 100 square feet of growing area, depending on the level of deficiency. Always obtain a soil analysis before adding magnesium sulfate to plants or garden beds, unless they exhibit obvious signs of magnesium deficiency. For indoor or container plants, apply magnesium sulfate at a rate of 2 tbsp. per gallon of water. Roses and tomatoes require 1 tbsp. per foot of plant height for each plant.

Efficacy Debate

• Although magnesium sulfate has been used to correct nutrient deficiencies in intensively cultivated areas for many years, some debate exists regarding its effect on plants in residential garden settings. A review of the published scientific literature, conducted by Dr. Linda Chalker-Scott of Washington State University, recently found that the popular conception of magnesium sulfate as a garden panacea is largely a myth. Studies indicate that its application is not warranted except in cases of soil deficiency or intensive cultivation.