In horticulture, gypsum is used as a soil improver. Gypsum works to improve the drainage and the physical structure of heavy, clay soils. By changing the way a heavy, clay soil behaves, gypsum helps to release nutrients that would otherwise be unavailable to plants. Being water soluble, the effects of gypsum are not lasting and gypsum needs to be reapplied every two to three years.
Gypsum can be spread over clay soils, but is more effective if dug into the soil. Spread at a rate of 1kg per square metre.