Sulfur is essential for turfgrass health, classified as one of the three secondary macronutrients alongside calcium and magnesium. Plants require these nutrients in relatively large amounts, though less than the primary macronutrients (nitrogen, phosphorus, and potassium). Sulfur impacts both the internal biochemical processes of the grass plant and the chemical environment of the soil. Managing its levels is important for maintaining a lush lawn.
Sulfur’s Role in Grass Growth and Color
Sulfur is a building block for numerous organic compounds in the grass plant’s metabolism. It is a structural part of the amino acids cysteine and methionine, which are required for protein synthesis. Without sufficient sulfur, the grass cannot produce the proteins needed for growth and development.
The nutrient is also directly involved in forming chlorophyll, the green pigment responsible for photosynthesis. A lack of sulfur limits the plant’s ability to manufacture this pigment, causing the grass to lose its deep green color. Sulfur is also required for the activation of several enzymes and helps the plant utilize nitrogen efficiently.
How Sulfur Changes Soil pH
Sulfur is used as a soil amendment to lower the pH of alkaline soils, a process known as acidification. This is relevant for turfgrass that thrives in slightly acidic conditions, typically with a pH range between 6.0 and 7.0. This pH reduction relies on the activity of soil bacteria.
When elemental sulfur is applied, specialized microbes, such as Thiobacillus species, convert the sulfur into sulfate through oxidation. The sulfate then reacts with water to form sulfuric acid, which lowers the soil’s pH level.
The resulting lower pH improves the availability and uptake of many other nutrients, especially micronutrients like iron and manganese, which are often unavailable in high-pH conditions. Acidification also enhances the grass’s ability to absorb and utilize nitrogen fertilizer. Since this process depends on microbial activity, it is slow and requires warm soil temperatures.
Recognizing Sulfur Deficiency in Your Lawn
A lack of available sulfur in the soil produces distinct visual symptoms in turfgrass. The most common sign is generalized yellowing, or chlorosis, of the grass blades. This yellowing typically appears first on the newest or youngest growth, rather than the older leaves.
This pattern of chlorosis is an important diagnostic detail, as it helps distinguish sulfur deficiency from nitrogen deficiency, which usually shows yellowing on the older leaves first. Other symptoms include stunted plant growth, resulting in a thin turf stand, and delayed spring green-up. When sulfur is deficient, the grass cannot properly convert nitrogen into proteins, leading to poor overall vigor.
Sulfur is highly mobile in the soil, often existing in the sulfate form which can be easily washed away by heavy rainfall or irrigation. For this reason, deficiencies are more likely to occur in sandy soils, which do not hold nutrients well, and in areas with low organic matter. Observing these symptoms suggests that a soil test is needed to confirm the sulfur level and determine the soil pH.
Applying Sulfur Amendments
Applying sulfur amendments is the primary way to correct a deficiency or adjust soil pH. The choice depends on the goal, with two main categories available: quick-release sulfate forms and slow-release elemental sulfur. Sulfate forms, such as ammonium sulfate or potassium sulfate, provide immediately available nutrition and quickly correct a sulfur deficiency.
Elemental sulfur, typically sold in granular form, is used for lowering soil pH. Because it must be oxidized by bacteria to form acid, its effect is slow and can take several months to fully manifest.
Application rates should always be based on a recent soil test recommendation. It is best to apply elemental sulfur in the spring or fall when soil temperatures support microbial activity. Never exceed a maximum annual rate of around 10 pounds per 1,000 square feet, as over-application can injure the turf. Always water the lawn immediately after application to wash the material into the soil.