Many fertilizers add nutrients mainly nitrogen, phosphorus and potash to the soil, but do little to change the soil structure. I thought it might be helpful to explain a few common, but often misunderstood soil conditioners. Gypsum - finely powdered rocks or the easier to handle pellets of calcium sulfate. Gypsum is mainly used to improve water penetration and aeration of clay soils. It helps by coaxing the fine particles of clay to stick together, so the soil has better structure.
Some gardeners swear by gypsum as a soil conditioner.
Peat - Also referred to as peat moss, sphagnum moss, sphagnum peat moss and sphagnum peat. Although these terms are often used interchangeably, there are some important differences. For the most part peat is dried plant parts harvested from bogs or wetlands. The material may be partially or fully decomposed and may be light brown to black. It is light-weight, fluffy and is known for its ability to retain moisture.