Decay of plant residue, the addition of organic matter, and the widespread use of nitrogen fertilizer also increases soil acidity. Most of North Carolina's landscape plants grow well in soil with a pH range from 6.0 to 7.0. Within this range, the essential nutrients are available to most plants, and soil organisms can carry out their beneficial functions. The analysis is always printed on the fertilizer label. Natural fertilizers generally originate from unprocessed organic sources such as plants or animals.
Synthetic fertilizers are man-made or processed.
Most nutrients from living or once-living organisms are not readily available for plant growth, because they are bound in organic molecules such as proteins and amino acids and in structures such as cell walls. These nutrients are released only when microorganisms decompose the organic matter. Slow-release fertilizers may be synthetic or natural. Because nutrients are released over an extended period of time, slow-release fertilizers do not have to be applied as frequently as other fertilizer types. Also, higher amounts of slow-release fertilizer can be added at each application without risking injury to plant roots.