Gypsum is a naturally occurring mineral composed of calcium sulfate, utilized as a soil amendment in lawn care. Its primary function is not as a traditional fertilizer but as a conditioner that improves the physical and chemical properties of the soil beneath the turf. Applying gypsum helps create a more favorable environment for grass roots to develop, supporting a healthier and more vibrant lawn. Benefits include structural improvements in heavy soils, delivery of necessary plant nutrients, and mitigation of salt damage.
How Gypsum Improves Clay and Compacted Soil
Gypsum is frequently applied to lawns with heavy clay or compacted soil to improve their physical structure. Clay soils often suffer from poor drainage because fine particles stick closely together, leaving little space for air and water movement. Gypsum facilitates flocculation, which is the clumping together of these tiny soil particles into larger, more stable aggregates.
This structural change is initiated by the calcium ions released from the gypsum, which displace other ions, such as sodium, bound to the clay particles. The calcium acts as a bridge, pulling the clay particles closer to one another and forming small, porous units. This formation of aggregates creates pathways and pore spaces within the soil profile, reducing density and easing compaction.
The resulting improvements translate directly into a healthier lawn environment. Better soil structure allows water to infiltrate the ground more easily, reducing surface runoff and ensuring moisture reaches the root zone. Increased pore space also enhances soil aeration, providing necessary oxygen for root respiration and helping beneficial soil microbes thrive. Gypsum promotes deeper root growth, which leads to a more resilient and drought-tolerant turf.
Essential Nutrient Delivery to the Lawn
Gypsum acts as a source of two essential macronutrients for turfgrass: calcium (Ca) and sulfur (S). Calcium is a fundamental component of plant cell walls, providing structural integrity and promoting strong, healthy root growth. A deficiency can hinder the development of new cells, leading to stunted or weakened grass.
Sulfur is equally important, playing a significant role in the production of chlorophyll, the green pigment necessary for photosynthesis. It is also a component in the synthesis of proteins and amino acids within the plant. Supplying sulfur via gypsum helps ensure the grass maintains its deep green color and efficiently processes nutrients.
Gypsum does not significantly alter the soil’s pH level, which is a major distinction from agricultural lime. While both amendments supply calcium, lime is used to neutralize soil acidity and raise the pH. Gypsum is pH neutral, allowing homeowners to supplement calcium and sulfur without risking an unfavorable change to the soil’s acid-alkaline balance.
Specialized Uses and Application Guidance
A specialized use of gypsum is mitigating damage caused by high sodium levels in the soil, often resulting from road salt runoff or high-sodium irrigation water. When excessive sodium is present, it causes clay particles to disperse, leading to severe compaction and poor water infiltration characteristic of sodic soils. The calcium in gypsum chemically displaces the bound sodium ions from the soil particles.
This displacement process forces the sodium into a soluble form, where it attaches to the sulfate component of the gypsum, creating sodium sulfate. This new compound is highly leachable, meaning it can be flushed out of the root zone with subsequent watering or rainfall. Using gypsum to reclaim sodium-affected soil is often more effective than attempting to physically break up the soil.
Applying gypsum to a lawn is straightforward and can be done any time of year, though spring or fall applications are common. A typical application rate is around 40 pounds of granular gypsum per 1,000 square feet, but a soil test can provide more precise figures. The granules can be spread using a standard broadcast spreader for even distribution. After spreading, the product must be thoroughly watered into the lawn. This watering dissolves the calcium sulfate, allowing the beneficial ions to move into the soil profile to improve structure and displace unwanted sodium.