What Is a Slow-Release Fertilizer?

Slow-release fertilizers provide a steady supply of plant nutrients over an extended period of time. They require fewer applications because the materials are held in the soil and gradually release the nutrients.

Slow-release fertilizers include:
• Natural organic fertilizers; and
• Fertilizers with 50% or more of the nitrogen as water-insoluble nitrogen (W.I.N.), or the equivalent.

This definition is recommended by the Healthy Lawn and Garden Technical Advisory Committee for use in Oakland and Wayne Counties. It reflects the experience of local experts as well as the experience of Eastern states in the Chesapeake Bay Region.

Why Use Slow-Release Fertilizers?

• To protect lakes, streams and groundwater
• To promote steady, uniform grass growth
• To provide essential nitrogen for building healthy turfgrass
• To avoid over-fertilization and “burning” of plants
• To protect soil microbial life and earthworms.

Slow-release fertilizers often save time and may save money in the long-run. Products may appear more expensive, but fewer applications are needed. If products include organic matter, the general health of the soil can be improved, thereby reducing the potential for pests and diseases.

Natural Organic vs. Man-Made Synthetic Fertilizers

The choice of natural, organic vs. synthetic (man-made) fertilizers is an individual one. The nutrients from organic and synthetic products are the same after they are released into the soil system.

Organic fertilizers increase the organic content of the soil, improve the physical structure of the soil, and increase the bacterial and fungal activity which benefits plant health. Organic nutrients depend on microbial organisms in the soil for material breakdown. Distributors of organic fertilizers can provide information about micronutrient content and other benefits.

However, organic fertilizers may not have nutrients immediately available to plants at the time of transplanting. Organic products may be more expensive than synthetic products.

Slow-Release Fertilizers for Homeowners – List Updated April 2007
The following fertilizers meet the recommended standards and are available in some local garden centers and hardware stores:
Click here for a 2007 fertilizer list in PDF format

For a useful link, go to www.landscape.org