JoAnne Skelly: Slow-release lawn fertilizers

My friend Marty and I were talking about clover in lawns yesterday. I mentioned that clover often indicates inadequate nitrogen levels in the soil.

He said that he does fertilize regularly but is careful not to overfertilize, because he lives on the shores of a lake.

This is conscientious of him because timing of application and amounts of fertilizers is important in order to avoid excess nutrients, not only nitrogen, but also phosphorus, getting into lakes and streams.

These nutrients can cause algal blooms that not only reduce water quality and clarity, but also harm water life. We started discussing organic versus inorganic fertilizers.

Organic fertilizers are released slowly over time naturally, while inorganic fertilizers can be quick or slow release. Slow-release fertilizers, whether organic or inorganic, are less likely to leach into water.

They keep nitrogen steadily available over a longer period of time, similar to a slow-release vitamin. Organic versions have lower concentrations of nutrients and may be made from composted animal manures, alfalfa meal, blood meal, feather meal, or soybean meal.

Activated sewer sludge, which is actually heat dried microorganisms that have digested organic materials in wastewater (not poop) is considered organic. Some organic products are inoculated with beneficial microorganisms, which can often make it easier for plants to take up nutrients.

An example of a slow-release synthetic is sulfur-coated or polymer-coated urea. It takes slow-release products longer to green up a lawn than quick release synthetic fertilizers such as ammonium sulphate.

Since plants take up their nutrients in the inorganic form, the source of the nutrients does not matter to the plant. However, organics also help build overall soil health, structure and water-holding capacity, something inorganic fertilizers don’t do. This improves plant hardiness.

Slow-release fertilizers, whether organic or inorganic, can reduce mowing frequency. Other benefits include the reduced risk of burning the grass, more sustained even growth, and less leaching into surface or ground water.

Less fertilizer may be needed over the entire season. However, they can cost more than traditional quick release synthetic fertilizers. Fall is always a good time to fertilize the lawn. Slow-release products are fine for this time of year.

On the other hand, I often use a 16-16-16, synthetic fertilizer in the fall to set up strong roots before the cold sets in and to ensure good healthy growth in spring. It’s easy to find and affordable. If you are only going to fertilize once a year, fall is the time to do it.

JoAnne Skelly is Associate Professor & Extension Educator Emerita at University of Nevada Cooperative Extension. Email skellyj@unr.edu.