Listen to any garden-related television or radio show, or read a reputable garden magazine, and you'll encounter many references to a product called Osmocote. Gardeners usually reserve the use of Osmocote, a more expensive synthetic fertiliser, for only their most prized bedding flowers, vegetables, houseplants or other container-grown plants. In the United States, Osmocote is sold and marketed by the Scotts Company of Ohio. In early 2011, the Osmocote brand and product was purchased by Everris International, a global horticultural corporation based in The Netherlands.
Osmocote looks like small, round peppercorns with a creamy beige colour. Rather than being called granules, Osmocote particles are known as prills. The beige shell on the prill coats a core of nutrients. Prills are scattered atop the garden soil or incorporated into the soil at planting time. As soil warms and rain or irrigation reaches the prills, the coating allows internal nutrients to trickle out into the adjacent soil -- via osmosis -- for plant roots to absorb.
As of 2011, three brand streams exist for Osmocote fertilisers. The original formulation is called Osmocote Classic and is the Osmocote that most gardeners know and use for everyday gardening purposes. It is a formulation of 19-6-12, correlating to percentage of nitrogen, phosphorus and potassium, respectively. Osmocote Plus is similar to the classic formula but with micronutrients, best used in nurseries for fast-growing annual plants. Osmocote Pro's N-P-K formulation is similar, but with large amounts of micronutrients more appropriate for widespread use in the landscape for both herbaceous and woody plants.
Whatever the Osmocote product or formulation, the fertiliser prill is coated with a polymer that changes porosity based on temperature. As moist garden soil temperatures warm, the pores increase in size to release more nutrients. This relationship to temperature correlates to increased growth of plants, thereby well-timing the nutrient release for use by plants. As soil cools, the pores tighten and fewer nutrients are released. Depending on the thickness of the polymer layer, the amount of nutrients in a prill can last for three to 12 months.
Osmocote Use Insight
In general, Osmocote fertilisers are not flippantly used across large expanses of the garden. Usually other well-balanced, quality slow-release fertilisers suffice with their nutrient formulas, and at a lower cost. Focus Osmocote fertiliser usage on fast-growing plants grown from spring to fall, or for healthy houseplants. Osmocote prills slowly release nutrients as long as the soil temperatures remain below 26.7 degrees Celsius. (REF 4, Tips sidebar) In hot summer regions, the warm soil temperatures hasten Osmocote prill degradation, shortening the longevity of the fertiliser in the soil profile. For example, if the soil is 29.4C, expect a product's usual three-month longevity to be reduced to one month.