Understanding Fertilizer Values for Better Results

— Written By and last updated by Emily Walter

With spring comes a list of outdoor resolutions and many have to do with lawn and garden projects that require some basic knowledge of fertilization.

All values in the fertilizer industry are based on 100 pounds, explains Duplin/Sampson Area Horticulture Extension Agent Tom Hroza. What this means is that a 100-pound bag of 8-8-8 contains 8 pounds of nitrogen, 8 pounds of phosphorus and 8 pounds of potash.

“When figuring how much fertilizer to apply to a yard or garden, I always recommend a soil test first. Soil test supplies are available at our local Extension offices and the analysis is free this time of year.” If that is not available, Hroza noted a general fertilization guide to use for untested plots. An example would be a centipede lawn.

“The recommendation is 1 pound of nitrogen per 1000 square feet. If our yard were 15,000 square feet we would need 15 pounds of nitrogen for the whole yard. If we used 8-8-8 we would need approximately 200 pounds, but we do not need the phosphorus and we need more potash. So a better choice would be an 8-0-24, we would still need 200 pounds to get our 15 pounds of nitrogen but in addition we would get 48 pounds of potash. We would be applying 1 pound of nitrogen and 3 pounds of potash per 1000 square feet which is what most of our soils need. If 8-0-24 is not available 15-0-14 will work, but we will not be getting as much potash as our lawn needs,” Hroza explained.

A high nitrogen fertilizer, such as 24-3-10, 16-4-8, are commonly packaged as a lawn product and is available in area stores. However, Hroza emphasized these high nitrogen products are not for centipede lawns because when used the grass does not go dormant when it should and results in winter kill.

Like prepackaged lawn fertilizers, another product available in area stores is a lawn weed and feed. Hroza also noted that weed and feed items are too high in nitrogen and have an early time-frame for application to achieve success from the product.

“If your applying this any time after the weeds germinates it’s too late to get good control. In our climate mid-March is getting late. Some weed and feed products need to be applied in the fall for best control. Another thing is these products are expensive to use and not achieve your desired results.”