Epsom salt contains two secondary nutrients important for plant life: magnesium and sulfur. This compound is highly water-soluble, allowing for easy absorption by grass roots when applied to the lawn. Understanding how and when to apply this material is essential for lawn care, as its use should be conditional rather than routine.
The Role of Magnesium and Sulfur in Lawn Health
Magnesium is the central atom within the chlorophyll molecule, the green pigment responsible for capturing sunlight during photosynthesis. Without sufficient magnesium, the plant cannot effectively convert light energy into the chemical energy needed for growth.
Magnesium also functions as an activator for many enzymes that regulate various plant processes, including the uptake of other nutrients and the transfer of sugars throughout the plant. Sulfur, the other component of Epsom salt, is necessary for the synthesis of proteins and certain enzymes. It is also a structural component of several amino acids.
Determining If Your Lawn Needs Epsom Salt
The frequency of application depends entirely on whether the soil has a confirmed deficiency of magnesium or sulfur. Applying Epsom salt without knowing the soil’s current nutrient balance is not recommended. A professional soil test is the most reliable tool for accurately diagnosing a nutrient deficiency, providing specific levels of magnesium, potassium, and calcium.
Visual symptoms can offer a clue, but they are not definitive. A magnesium deficit often manifests as interveinal chlorosis, where the tissue between the veins of older grass blades turns yellow while the veins remain green. Since magnesium is a mobile nutrient, the plant moves it from older leaves to newer growth, causing the initial yellowing in the older foliage.
Soil pH levels also influence magnesium availability. High acidity (low pH) can reduce the uptake of magnesium by the grass roots. Conversely, high levels of potassium in the soil can restrict magnesium absorption, even if the total content is adequate.
Recommended Application Frequency and Technique
Epsom salt should only be applied to a lawn once a soil test confirms a magnesium deficiency. If a deficiency is present, a typical application frequency is once or twice per year during the growing season, usually in the spring and early fall. The application should stop once the soil’s magnesium levels are restored to an optimal range, which the follow-up soil test will determine.
There are two primary ways to apply magnesium sulfate to the turf.
Granular Application
For granular application, a common rate is to spread approximately half a pound of Epsom salt per 100 square feet of lawn area. This dry material must be immediately watered into the soil to prevent salt burn on the grass blades.
Liquid Spray Application
A liquid spray allows for quicker nutrient uptake. A standard mixture involves dissolving about two tablespoons of Epsom salt in one gallon of water for spot treatments or broadcast spraying. Apply the solution evenly over the turf, preferably in the late afternoon or on a cloudy day to minimize the risk of scorching the leaves.
Potential Drawbacks of Over-Application
Applying Epsom salt unnecessarily or excessively can lead to negative consequences for the lawn. A primary concern is nutrient antagonism, where an excessive amount of one nutrient interferes with the plant’s ability to absorb others. Too much magnesium can inhibit the uptake of other essential elements, particularly calcium and potassium.
An imbalance in the calcium-to-magnesium ratio can negatively affect soil structure and turf health. Furthermore, because Epsom salt is a salt, applying too much granular product without sufficient water, or using a concentrated liquid solution during hot, sunny conditions, can cause the grass blades to dry out and brown, resulting in salt burn.