Organic fertilizers are derived from plant and animal parts or residues (cow and chicken manure, alfalfa pellets, compost, grass clippings, bat guano). Synthetic fertilizers are man-made (ammonium nitrate, potassium sulfate). A plant cannot recognize one form from the other. Plants require nutrients just like us. Nitrogen, phosphorous, potassium, magnesium, calcium, sulfur, iron, copper, boron, chloride, manganese, molybdenum and zinc are all necessary, with the first six being considered macronutrients and the remaining being micronutrients. I repeat, all plants process nutrients in the same way, whether they come from an organic fertilizer or synthetic fertilizer. I like to describe the major difference this way: if you are very sick and in the hospital, your only source of nutrition may be from an IV drip that delivers the nutrients quickly to your system. If you are healthy, you could eat a serving of beans and vegetables and wait for your digestive tract to break down these items into nutrients that your cells can then absorb. The same is true for plants. A healthy plant can wait for chicken manure to be broken down by soil microbes into the nutrient form. A severely stunted plant is better treated by a fast release synthetic fertilizer. I believe both uses are applicable.
Organic fertilizers improve soil quality, water retention, nutrient retention and, not only feed the myriad living soil organisms but add to their numbers as well. At the same time, they offer a dilute source of nutrients, can be both messy and expensive, and nutrient release is dependent on microbes whose activity and health is dependent on temperature and moisture content. Synthetic fertilizers offer a quick nutrient source but do not amend the soil quality or promote microbial activity. They are easy to over-apply, resulting in burning of plant tissue, not to mention that they are fast to leach out and run off into nearby waterways. Both organic and synthetic forms can keep plants healthy. One is not bad and the other good. Both can be good when applied properly.
If a grower uses both, the label “organic” cannot be applied. But, is the quality of the product any less than those bearing the USDA certified organic label? This type of agriculture is considered “sustainable;” growers can use labels stating that the product is sustainable and pesticide-free. I applaud their conscientious efforts, and do not hesitate to buy their products, as there is little to no difference between their quality products when compared to those bearing the USDA organic label.