This brief discussion is an introduction only to a broad field of study which has resulted in some but not enormous technologies. Microbes and enzymes are not considered in this report. By and large, foliar applications of substances which may stimulate growth or fruiting are not specifically considered at this time. Of concern mostly are those that may be applied in soil or both ways. Some composts are believed to contain biostimulants which is a basis for claiming that adding composts to soil is better than adding non composted materials.
Some specific categories are gibberellins, cytkinins, and auxins.
Biostimulants are materials that promote plant growth when applied in small quantities. They also help plants withstand harsh environments. Although researchers knew as early as 1913 that plants produced a cell division-stimulating substance, it took until 1955 to identify it as a cytokinin. In 1963, scientists isolated zeatin from corn. It was the first example of a naturally occurring cytokinin.