Lawn fertilizer selection (3-22-10)

Proper fertilization is a key factor in keeping your lawn healthy and beautiful. However, you should always have a purpose for applying fertilizer whether it is to establish a new lawn, encourage growth from excessive wear or pest damage, or simply to maintain color and health. The turf species, the growing zone you are in, and the source of fertilizer you use will also dictate your fertilization program.

There are many different types of fertilizers with varying amounts of the essential nutrients within them, but the three numbers marked on the bags always represent the percentage of nitrogen, phosphorous, and potassium. Generally, most warm season turfgrasses prefer a ratio of 4-1-2 of N-P-K so keep this in mind when selecting a lawn fertilizer.

Plants, including our lawn grasses, can’t tell the difference in elemental nitrogen once it becomes usable by the plant. However, there is considerable difference in the types of fertilizer sources and their release of nitrogen to the plant.

Nitrogen fertilizer sources are classified as either readily available or slow release.  Products such as ammonium nitrate, urea, and ammonium sulfate are very water-soluble and become available very quickly.  The advantages of such fertilizer sources are that they are generally less expensive per pound of actual nitrogen and plants respond very quickly following an application.  Disadvantages are that they have greater burn potential, have a greater risk of leaching, and do not give extended results. 

Slow-release formulations primarily contain nitrogen sources that are not immediately available to the turf.  The oldest slow-release products are natural fertilizers such as compost, cottonseed meal, sewage sludge and manures, which release their nitrogen as the microorganisms in the soil break them down.  Other sources combine urea with formaldehyde while many of the more modern products contain quick-release nitrogen forms that have thin plastic, sulfur, or resin coatings that allow water to dissolve them slowly. 

The main thing to remember is that all these slow release products will release their nitrogen over a longer period of time and provide more uniform vegetative growth to the turf without the potential of turf injury from over fertilization.  The initial costs of these products are generally higher, but they perform much longer and reduce flushes of growth that encourage disease attack.

For more details on selecting the right fertilizer for you turf species or growing zone refer to Extension publication #1322.

Published March 22, 2010

Dr. Wayne Wells is an Extension Professor and Turfgrass Specialist. His mailing address is Department of Plant and Soil Sciences, Mail Stop 9555, Mississippi State, MS 39762. wwells@ext.msstate.edu