The sheetrock used to build your walls is made of gypsum. This same material can be used in your garden or lawn to benefit the soil. It may help loosen the soil and promote better water drainage. Gypsum is made up of calcium and sulfur, both naturally occurring elements. When applied to soil, ground gypsum works with other soil amendments to create a healthy environment for good bacteria and microbes.
Gypsum improves the structure of clay or heavy soils. The calcium in gypsum creates "space" between the sand, silt and clay particles in compacted soils. The humus in these soils, then, is able to integrate more fully, making for looser soil. Humus in soil is made up of the organic particles that provide stability. Humus is rich in nutrients and gypsum helps plant roots access those nutrients by loosening the soil structure.
One application of gypsum, however, will not miraculously change your clay soil into a rich loamy garden soil. Gypsum works over time and must be reapplied annually. It may take up to three years for gypsum to fully condition your soil.
Used as a fertilizer, gypsum provides calcium and sulfur directly to the soil, but it is not a plant fertilizer. Rather, by supplying nutrients to the soil, plants are better able to access nitrogen, iron, zinc and other essential nutrients.
The improved soil structure allows for a better draining soil; this means plant roots are less likely to be waterlogged or subject to rot. Well-draining soil also retains its structure, thus reducing surface crusting or clumping.
When soil doesn't crust over or clump, roots tend to grow thicker and burrow deeper into the soil, making for a stronger, healthier root system. The plant, then, is able to devote energy to producing foliage and fruit, rather than working to develop roots and force nutrients through a weak root system.
Healthy soil is neither too alkaline nor too acidic, but neither is it without salt or acid. Gypsum has the ability to adjust the balance of soils that may be out of balance.
If a soil is too alkaline, gypsum will counteract and promote a more acidic environment, lowering the pH balance. If the soil is too acidic, perhaps a result of over-fertilization, gypsum will counteract and raise the pH level.
Gypsum works to realign soil's natural pH balance. Indigenous plants have certain pH balance requirements and using gypsum as a soil amendment may aid in the soil's ability to achieve the pH balance needed for the plant's life.