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Organic Soil Supplements

By Fern Fischer ; Updated September 21, 2017
Deep rich topsoil
the field image by Angela Suppan from Fotolia.com

All soil needs to be improved with supplements for optimum plant growth. Adding compost and humus improves the soil composition, improving its tilth and texture. Compost also contains some nutrients as well as active microbes that are necessary for healthy organic soil and good plant growth.

Soil should also be amended with organic micronutrients and mineral supplements. They improve the soil’s capacity to retain water and dissolved nutrients, and they improve the ability of plants to use those nutrients.


Agricultural gypsum contains approximately 23 percent calcium and 18 percent sulfur. These minerals raise the pH of soil, making it less acidic. Gypsum applications loosen heavy clay soils, improving the penetration of moisture and nutrients. In some cases, gypsum will increase the calcium in the soil without altering the soil pH. Gypsum can remove fertilizer residues from alkaline soils that carry a high content of salts from chemical fertilizers. Garden gypsum quickly improves garden soil that has been ravaged by synthetic chemical garden products.


Greensand may also be used to loosen clay soil. Greensand contains about 3 percent potash, and it also has over 30 important trace minerals. The term greensand is a common name for the mined mineral glauconite, or natural iron-potassium silicate, which is found in dry areas that were once part of the ocean floor.


Agricultural lime is derived from different sources. Oyster shell lime is powdered oyster shells, a byproduct of the seafood industry. It contains 36 percent calcium and dozens of nutrients and micronutrients in a natural balance from the sea. Dolomite lime is powdered, premium-grade dolomitic limestone, a good source of calcium and magnesium. Both types of agricultural lime raise the pH, making soil less acid.

Rock Phosphate

Nearly all soil is low in phosphate. Soft rock phosphate remains in the soil without leaching away, but it becomes depleted from plant use. One application of rock phosphate can last for up to 10 years. Phosphate helps plants develop strong root systems, and it is necessary for plants to produce good quality fruits and flowers. Phosphate also promotes beneficial soil bacteria and a healthy earthworm population.


Some plants, such as azaleas, and blueberries, require acidic soil. Elemental sulfur lowers the soil pH, increasing the soil acidity. The garden sulfur available at garden centers is sometimes blended with bentonite as a binder to aid in product flow during spreader application.


Plants must have magnesium to produce chlorophyll for photosynthesis. Magnesium makes phosphorus and nitrogen more readily available to plant roots, aiding in the absorption of these nutrients. A good source of both magnesium and sulfur is Epsom salt, which is magnesium sulfate.


About the Author


Fern Fischer's print and online work has appeared in publications such as Midwest Gardening, Dolls, Workbasket, Quilts for Today and Cooking Fresh. With a broader focus on organic gardening, health, rural lifestyle, home and family articles, she specializes in topics involving antique and modern quilting, sewing and needlework techniques.