When applied to a lawn, gypsum reduces soil compaction, improves soil structure and increases air movement. It also helps prevent excess water runoff by preventing the soil from forming a crust.
Gypsum can reduce the level of sodium in a lawn to help reduce its harm on plants and grass. Sodium blocks the grass from absorbing water deep in its roots, which is exacerbated in the winter when road crews use salt for road safety. The best time to use gypsum on a lawn is after it is aerated. This allows the lawn to absorb the gypsum deeper, instead of just at the surface level.