Gypsum is a mineral widely used in agriculture and gardening as a soil amendment to improve soil health and plant growth. The material, known chemically as calcium sulfate dihydrate, has been applied to soils for centuries as a source of two essential plant nutrients. While traditional powdered gypsum is effective, it presents challenges for handling and application due to its fine, dusty nature. Pelletized gypsum represents an advanced, user-friendly format that makes the product easier to spread and more effective in a variety of settings. This specialized form allows gardeners and farmers to apply the beneficial mineral precisely.
Composition and Difference from Powdered Gypsum
Gypsum is composed of calcium sulfate dihydrate, which provides approximately 23% calcium and 17% sulfur in its pure form. The powdered form is created by crushing and finely grinding the mined or synthetic mineral, resulting in a product that is highly susceptible to wind drift and difficult to handle. This fine powder requires specialized equipment for even distribution, and the dust can be a concern for operators and nearby areas.
The pelletized form is created by taking this fine powder and mixing it with a binder, such as lignosulfonate, and moisture in a process called wet granulation or agglomeration. The mixture is forced through a die or tumbled in a pan granulator, forming uniform, dust-free granules. This process transforms the messy powder into a free-flowing product that can be easily handled and blended with other granular fertilizers.
The physical change imparted by pelletization makes the gypsum suitable for standard broadcast spreaders used for lawn and garden applications. These uniform pellets significantly reduce dust exposure during handling and ensure a much more even spread pattern across the soil surface. Once applied, the pellets are designed to break down rapidly upon contact with water, releasing the fine gypsum particles into the soil where they can begin working.
Essential Roles in Soil Structure and Chemistry
Once dissolved into the soil solution, the released calcium and sulfate ions begin to provide significant physical and chemical benefits to the soil environment. The calcium component plays a prominent role in improving soil structure, particularly in heavy clay soils. Calcium ions cause clay particles to flocculate, meaning they clump together to form larger aggregates.
This aggregation creates larger pore spaces within the soil, which leads to improved aeration and enhanced water infiltration and drainage. Better soil structure helps reduce surface crusting, which can otherwise impede seedling emergence and prevent water from soaking deeply into the root zone. Furthermore, the application of gypsum provides the plant-available nutrients calcium and sulfur, which are often depleted through cropping and leaching.
Gypsum remediates problematic soils without altering the soil pH, as it is pH neutral and can be used on both acidic and alkaline soils. It is particularly effective in reclaiming sodic soils by supplying calcium, which replaces excess sodium ions on the clay exchange sites. The displaced sodium then leaches away as soluble sodium sulfate, improving the soil’s physical condition. Gypsum also helps mitigate aluminum toxicity in highly acidic subsoils, allowing plant roots to penetrate deeper and access more water and nutrients.
Guidelines for Application and Spreading
The pelletized nature of gypsum simplifies the application process for the home gardener and commercial operator. Because the product is free-flowing and uniformly sized, it can be applied using any standard rotary or broadcast spreader. This eliminates the need for specialized equipment typically required for dusting powdered materials, ensuring an even distribution across the target area.
For the active ingredient to reach the soil, the pellets must be dissolved, which happens naturally with rainfall or irrigation. Watering the area immediately after spreading helps break down the pellets quickly, moving the gypsum into the soil profile where it can start interacting with clay particles. While application rates vary based on specific soil needs, a common maintenance application for turf or gardens is often between 25 to 50 pounds per 1,000 square feet annually.
The ideal time for application is generally in the spring or fall, though it can be applied anytime the ground is not frozen and conditions allow for even spreading. For severely compacted or sodic soils, higher corrective rates may be necessary, and soil testing is always the best way to determine the precise amount required.