Gypsum is a naturally occurring mineral that is also known as selenite and alabaster. The word "gypsum" is derived from the Greek word for a calcified mineral. "Selenite" comes from the Greek word that means "moon rock," because of the mineral's pearly surface. Ground gypsum is used in the garden to improve soil conditions.
Use on Clay Soils
According to an article by Linda Chalker-Scott of Washington State University, gypsum improves clay soil by altering its structure and fertility. She says this is especially true of clay soils that are overworked due to intensive crop rotating. In regions where the soil is naturally dense and clay-like, gypsum sprinkled atop the soil and watered in makes the soil easier to work and plant in.
Chalker-Scott says gypsum also aids in removing excess sodium from the soil. Gypsum leaches out the salt and replaces it with calcium, which is beneficial to crops. This is particularly helpful in coastal regions, where salt air and proximity to water make local soils sodic (saline).
Gypsum is applied topically to soil, using a hand- or push fertilizer spreader. For best results, the granules should be spread at a rate of 40 pounds per 1,000 square feet. Gypsum only needs to be applied once per year, any time of year. After spreading, the gypsum should be watered into the ground immediately, so it can begin to penetrate the soil.
Gypsum is safe and non-toxic to both humans and animals. It is safe to spread gypsum in the yard and around established plants; it will not affect the growth or development of plant life. Because it is a fine, granulated powder, users should don particulate-rated face masks when working with gypsum. Precautions should be used when working with any particulates, even if they are non-toxic. This is especially true for people with asthma or other lung-related diseases.
Besides its use in the garden, gypsum is a key ingredient in other products. Ground gypsum is used in sheetrock (also known as drywall) used in home construction. Gypsum is not a good conductor of heat or cold, which makes it a good insulator. The mineral is also used in paint fillers, some types of cement and plaster of Paris.