The use of fish as a fertilizer is thought to have been pioneered by Native Peoples, but the practice certainly has a place in contemporary gardens.
The primary value of fish based fertilizer is one shared by many organic nutrients. That is, it improves soil health by fostering microbial life, which in turn break down complex organic molecules, and so improves soil fertility.
Further, research has shown that organic fertilization not only benefits soil biota populations, but actually fosters beneficial biological organisms, while simultaneously reducing the load of pathogens. Another improvement stemming from the life building qualities of organic inputs, is that the soil biota improves soil structure. Examples abound.
For instance, the movement of worms through the earth provides avenues for both gaseous exchange, and the movement of water. Arbuscular mycorrhizae produce glomalin, which acts as a sort of glue, and therefore binds soil elements into a cohesive whole. In essence then, it might be fairly said that organic inputs are an integral component of, and act in accordance with, the evolutionary milieu that plant life has developed in.
Despite needing the assistance of beneficial biology, fish based fertilizers rival “chemical” fertilizers in their ready availability. Even better is the fact that such products offer a relatively safe non-burning form of nitrogen. Many also provide phosphorous, potassium, calcium, magnesium, and trace elements.
Although most commonly found in liquid form, dry granular products are available. These are ideal for those gardeners that like to build their own soil, or wish to employ traditional top dressing.