Nutrient Value of Gypsum Fertilizer

Gypsum, or calcium sulfate, adds nutrients to your garden or lawn while improving drainage. Apply 2 to 4 pounds of gypsum per 100 square feet by hand-broadcasting it on the surface of the soil or lawn, or by using a seed-spreader to apply it to the surface. Watering the gypsum in is the last step, after which your lawn and garden plants can begin reaping gypsum's benefits.

Gypsum is composed of about 23 percent calcium. A lack of calcium in the soil leads to blossom-end rot. This plant disease is especially troublesome in tomatoes, eggplant and peppers, and causes the bottoms of these vegetables to turn black. Calcium deficiency also affects foliage. Generally, the newer leaves at the top of a plant will become misshapen. For ornamental plants or for leafy edibles, preventing this damage is especially important.

Gypsum doesn't improve drainage by adding bulk to soil, as compost does. Instead, the calcium within gypsum neutralizes some of the sodium in clay soils. This is important, because excess sodium results in small, tightly packed particles. The compacted particles prevent water from passing from the soil surface to plant roots. By lowering sodium content, calcium allows for the larger, more well-spaced particles that encourage proper drainage.

Sulfur makes up 19 percent of gypsum's composition. Plants growing in sulfur-deficient soil don't grow as quickly as plants growing in soils with sufficient sulfur. The plants are also less sturdy in low-sulfur garden beds, and may experience overall yellowing, or yellowing on the upper, younger leaves. Sulfur assists in the absorption of nutrients such as nitrogen. In areas where sulfur is severely low, plants also can't take in enough nitrogen for healthy growth.

For gardens that have alkaline, or "sour" soils, gypsum makes a better calcium amendment than limestone. Limestone, used in some areas to treat calcium deficiencies, is also used to raise the pH level of acidic, or low pH, soil. If your soil is already on the alkaline, or high pH, side, however, adding limestone for calcium can have the side effect of raising the pH even higher. This increased alkalinity creates an inhospitable environment for most plants. Gypsum, on the other hand, does not raise the pH level of soil.