The distinction between natural and synthetic fertilizers is somewhat arbitrary. It’s very hard to craft a definition of “natural” that includes all the fertilizers that most people consider natural and excludes those they consider synthetic. In general, synthetic fertilizers are products that have been changed substantially by chemical means. For example, phosphate rock fertilizer has been changed from its natural state by being ground into a fine flour, but hasn’t been changed chemically. The addition of acid to make it more soluble changes it chemically into superphosphate, a synthetic fertilizer.
(The word “organic” is often used synonymously with “natural,” but is used in this work to mean “derived from a plant or animal,” a more accurate definition. By the former definition, rock phosphate fertilizer is organic, but by the latter definition, it is not. For more information, see What does “Organic” Mean?)
The Origin of Synthetic Fertilizers
The first synthetic fertilizer was invented by John Lawes in 1842 when he patented a process for treating ground bones with acid to make superphosphate. At the turn of the twentieth century, the world’s demand for nitrogen fertilizers was beginning to outstrip its supply. At that time, much of the world’s nitrogen fertilizer was from an enormous deposit of bird droppings, 5 feet deep, along 220 miles of the Chilean coast. Fritz Haber, a German chemist, applied himself to the problem of fixing atmospheric nitrogen and developed the process still used today for converting atmospheric nitrogen into ammonia. In 1918 he was granted the Nobel Prize for this discovery.
Complete and Incomplete Fertilizers
Today, synthetic forms of plant nutrients form the basis for most commercial fertilizers. Most of these raw materials are available to home gardeners also, as ammonium sulfate, ammonium nitrate, ammonium phosphate, superphosphate, potassium chloride, potassium nitrate, and other chemicals. In this form, they are inexpensive, but sometimes inconvenient to use, and can damage plants if not used correctly. These fertilizers are called incomplete fertilizers because they don’t supply all the primary plant nutrients.
More commonly, gardeners buy more refined fertilizers formulated for specific crops or specific uses, such as houseplant fertilizer, citrus fertilizer, or winter lawn fertilizer. These products may be blends of natural and synthetic materials, and are designed to be used in specific ways. Most have directions on the label, and should be used in accordance with those directions. These fertilizers are called complete fertilizers because they usually contain a mix of primary nutrients.