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The Benefits of Adding Gypsum to Clay Soil

Nearly everyone who has a garden in the Southeastern United States is familiar with clay soil. The heavy, dense soil that covers much of the Southeast has many benefits; however, it requires amending for ornamental and vegetable plants to thrive. Calcium sulfate, commonly known as gypsum, can improve soil structure over time when applied to clay soils. It also provides a soluble source of calcium and sulfur, which are essential nutrients for plant vitality.

Gypsum is made up of calcium, sulfur, and water. This composition makes it particularly mobile in soil. Unlike lime, which is often used to add calcium to soil, gypsum does not affect soil pH. Gypsum is also able to move relatively quickly through soil particles and into the plants via their root systems. Sulfur is necessary for chlorophyll development and protein synthesis in plants. Sulfur deficiencies result in yellowing and dropping foliage and reduced foliage and flower production. Calcium is crucial to build resilient and strong plant tissue. Calcium deficiency results in weak and contorted new growth, as well as rot in fruiting plants. Both of these nutrients are critical for plant health and vibrant foliage, and both are found in gypsum.


Gypsum also fosters a more stable and workable soil structure, resulting in healthier plants. Clay soils are made up of tiny negatively-charged particles. These particles are extremely efficient at storing nutrients, however, they often lock nutrients into the tight clay soil structure, rendering them inaccessible to plant roots. Gypsum lightens clay soil, creating looser soil aggregates. This more friable soil structure is not only easier to work with, it also leads to more efficient nutrient exchange between plants and soil. Improved soil structure allows plant roots to expand and cover more mass, allowing the plant to build more mycorrhizal relationships and to reach more nutrients.


Good soil structure not only helps with nutrient exchange, it also improves drainage and moisture retention in clay soils. Clay soil particles bond together so tightly that water cannot penetrate the upper crust of the soil to reach plant roots. This causes a number of issues-erosion, pooling, and hardening of the top layer of soil in a garden bed. Gypsum creates a looser aggregate structure that water can flow through more freely. It breaks up clay particles, allowing water to drain through the soil to saturate plant roots.


EarthMix® Landscape™ premium soil conditioner contains gypsum. In addition, it contains a light blend of nutrient-dense composts and beneficial microorganisms. It can be mixed 1:1 for poor soils, or 1:3 to enhance good soil. Planting a tree or shrub? Backfill with a 1:3 ratio of Landcape™ premium soil conditioner and native soil to encourage root expansion. Landscape™ premium soil conditioner can also be used to lighten and enrich native soil in vegetable and ornamental garden beds.

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