Gypsum, a mineral that has been the source of controversy in the agriculture world, is a recommended lawn care additive. Gypsum's ability to soften soil by breaking up and loosening the structure allows the mineral to help revitalize tired lawns over a long period.
Gypsum is an extremely soft mineral created in nature as a byproduct of sulfide oxidation. Known as hydrous calcium sulfate, selenite or satin spar, it is often found in large masses. Common all over the globe, domestic sources are found in Oklahoma, Iowa, Nevada, Texas and California. Well-used in the manufacturing sector, gypsum is the primary material in chalk, plaster of Paris, plaster, sheetrock (wallboard), glass and is a key additive in Portland cement. A large portion of the gypsum market is the agriculture sector, including use by backyard gardeners.
Proponents of gypsum use include the Western Farm Press, which touts numerous benefits of the mineral. Two of the elements commonly found in gypsum are calcium and sulfur, both essential for lawn and plant growth. The use of gypsum improves structure in highly compacted soils by causing sand, silt, clay and other partials to band together, improving vital air movement. The mineral counteracts acidity by leaching into the subsoil and replacing aluminum as well as other acid-forming ions, which, in turn, allows roots to successfully penetrate previously stiff soil.
On its own, gypsum contains no plant nutrients so you don't need to worry about burning your lawn or applying too much. Applications can take place with or without fertilization. Non-toxic gypsum is safe to handle without protection and safe for use around pets and children.
Available in several forms (granular, flake, powder), the best choice for a lawn is the granular form because it tends to anchor itself to the soil and not blow or wash away before it can break down. Using a broadcast or drop spreader, the mineral should be applied at 40 pounds per thousand feet. While over-application will not hurt your lawn, one application per year is sufficient. Application can take place any time of the year in cold, temperate or hot weather. A lawn should be watered shortly after application to dissolve the grains and to let the mineral leach into the topsoil.
The Agriculture Center at Louisiana State University reports that applying gypsum to most soils will have little effect due to the all-too-common mixture of non-native and native subsoils throughout the United States. These layered soils show little effect from gypsum, as they are already loose and uncompacted. Exceptions are the arid portions of the western United States and some coastal areas. Pure gypsum is neutral and does not raise soil pH; however, some impure gypsum may contain dolomite, which will raise soil pH. Unwittingly using impure gypsum can create a potential problem for gardeners attempting to maintain low pH levels in their soil. Gypsum is over-prescribed at garden centers for a variety of soil problems, many of which the mineral cannot cure or curb. The LSU Agriculture Center recommends core-aerifying in the spring and summer to reduce soil compaction. Aerifying machines can be rented locally in most communities.