Gypsum, a natural mineral mined all over the globe, is an inexpensive, safe soil-additive that can break up compacted earth. Commonly used in lawn and garden care, the product is not without controversy--its effectiveness and misapplication are subjects of debate among agriculturists.
Gypsum occurs naturally as a byproduct of sulfide oxidation. Also known as hydrous calcium sulfate or selenite, the mineral is found in shale beds and mined worldwide. Leading state producers in the United States include Oklahoma, Iowa, Nevada, Texas and California. The primary use of gypsum is to manufacture sheetrock but it can also be found in chalk, plaster of paris and portland cement. An excellent source of calcium, gypsum is heavily used in agriculture because of its ability to break up compacted soil and allow for better root growth.
Gypsum provides two necessary elements to soil--sulfur and calcium--but its ability to break down compacted soils, in particular clay, into small particles makes it an important asset. In addition to clay, gypsum can be useful around new homes where the soil tends to be compacted by heavy machinery. In addition, fill dirt used to level out landscapes often contains unwanted clay. Gypsum applied over a three-year span can break up the clay, soften soil and permit proper drainage.
Gypsum is commonly misconceived as a fertilizer, but it contains no plant nutrients and only two elements (sulfur and calcium), so there is no danger of burning your lawn or crops. Accidental over-application should not produce any significant problems. Gypsum can be applied in warm or cold weather at any time of the year. Organic and non-acidic, gypsum is non-toxic and will not effect pets or children.
Gypsum for agriculture is milled in a granular form that aids in application. Best distributed by a drop or broadcast spreader, the recommended application for a turf lawn is 40 pounds per 1,000 feet. Garden application can be done by hand or a hand spreader. To distribute the gypsum by hand, grab a handful with a loose grip and flick the grains evenly across the garden as if dealing cards. Once distributed on the lawn or garden, there is no need to work it into the soil. Instead, just apply water and allow the grains to dissolve and leach into the soil naturally.
As simple as gypsum is, it is not without controversy. Several agriculture experts, including those at the Agriculture Center at Louisiana State University, consider gypsum an unnecessary additive. They contend that most soils in farms gardens and lawns are mixtures of non-native and native subsoils called "layered soils," which show little benefit from gypsum as they are already loose. In addition, pure gypsum is neutral and does not raise soil pH, but many gypsum products are impure and contain dolomite, which can raise soil pH, possibly creating an adverse environment for a garden. The basic rule of thumb is to use gypsum only in soils with large amounts of clay.