Fertilizers play significant roles in managing yard and garden plantings. Making proper decisions during the growing season not only impacts plant growth but can also impact the environment. When considering nitrogen fertilizer use, some frequent questions often arise.

For example, are lower-analysis fertilizers (containing less nitrogen) safer to use than higher-percent nitrogen fertilizers? More than one factor comes into play to answer this question. The first of the three numbers on the package is percent nitrogen. If one fertilizer has twelve percent nitrogen and another product has 24 percent nitrogen, then less material needs to be applied with the second product to supply the same amount of nitrogen to the plant. So, always adjust your rate being applied based on the percentage nitrogen in the fertilizer.

Another key component to answering that question is what kind of nitrogen is in the product. Fertilizer nitrogen is not immediately available for plant use, as it must go through conversion typically to nitrate, driven by beneficial bacteria in the soil. Two categories of nitrogen fertilizer carriers (nitrogen sources) include fast and controlled-release. Fast or quick- release nitrogen, as the name implies, becomes available quickly, which does increase potential plant injury if too much is applied. Examples include urea, ammonium nitrate, and ammonium sulfate. These materials have high salt indexes, indicating higher potential of burn if misapplied.

Conversely, controlled-release nitrogen sources are much slower in making nitrogen available to plants after being applied to the soil. Terms including slow-release, slowly available, and water insoluble nitrogen (WIN) all refer to controlled-release. Potential risk of plant injury is significantly less due to exceptionally low salt indexes and slow conversion of available nitrogen for plants. Examples include sulfur coated urea, coated urea, IBDU, and ureaform, among others. Many organic nitrogen fertilizers contain WIN and are controlled-release, including activated sewage sludge (Milorganite).              

Which is better, liquid- or granular-applied fertilizer? To accurately answer, compare the guaranteed analysis listing of all nitrogen sources in each product (found on the package), rather than application form. Both fast and controlled-release nitrogen sources are available for either liquid or dry (granular) application. Some liquid applied products are clear solutions, other are cloudy due to suspended particles. Without knowing the kind(s) of nitrogen in fertilizers, an accurate comparison cannot be made.

When fertilizing plants, research and understand the amount of nitrogen your yard and garden plants require. Choose quality materials and apply them cautiously using proper rates applied at the correct time. Avoid application near bodies of water or having fertilizer land on streets, sidewalks, and other impervious surfaces that drain into waterways.