Alkaline Soil and Chloride-Based Fertilizers
Alkaline Soils and Chloride Salts
Potassium in fertilizers comes from two sources: potassium chloride or potassium sulfate. The vast majority of fertilizers are formulated with potassium chloride (also called "muriate of potash" to hide its true name). The reason for this is cost: potassium chloride is cheaper than potassium sulfate. However, using potassium chloride means the fertilizer is adding chloride ions to your soil. Chlorides are plant toxins and contribute to the alkalinity of soil. Our soils in Kern County are already alkaline. Alkalinity causes poor growth, browning of shrub and tree leaves, and in extreme cases, the death of plants. Adding potassium chloride makes a bad situation worse. Because of this problem with potassium chloride, Gardener's Supply custom-blends the fertilizers we sell so that they contain potassium sulfate. The sulfur in potassium sulfate is a plant nutrient, often called the "fourth number" in a fertilizer formula. Sulfates do not contribute to the build-up of alkaline fertilizer salts. Sulfur is also necessary for the plant to metabolize nitrogen in the growing process.
The advantages of sulfates over chlorides has been demonstrated time and time again by professional gardeners who compare Gardener's Supply products with others on the market. Invariably, when our fertilizers are used in close proximity to other brands (see photo below), the difference is obvious: our fertilizer outperforms the competition every time!
