All begin as a granular complete fertilizer, which is normally composed of ammonium nitrate, ammonium phosphate, calcium phosphate, and potassium sulfate. The coating's thickness, along with temperature, determines how long the fertilizer lasts. Compared to other controlled-release fertilizers, Osmocote releases more nutrients in cooler soils. Several formulations are available, and all are based on fertilizers such as urea, ammonium nitrate, ammoniated phosphates, potassium sulfate, potassium nitrate. The green pellets have a thin, hard, and nearly break-resistant polymer shell.
Nutrient release is regulated primarily by temperature, allowing extremely predictable results.
Depending upon the formula, the green particles release nutrients for three to nine months at 86 o F. Polyon is marketed to home gardeners as Pursell's Sta-Green. Both are made by spraying molten sulfur onto granular urea. SCU is relatively inexpensive and is a component of various brands of home lawn fertilizers. As its name states, polymer-encapsulated SCU is coated with a thin polymer layer, a step that makes it last longer. Both SCU and polymer-coated SCU are used in many lawn and garden fertilizers.