Fish Emulsion as a Plant Fertilizer

Overview

Fish emulsion is a "natural" garden fertilizer made from byproducts of the fishing industry. Fish emulsion is touted as an all-purpose organic fertilizer since it is made from all-natural ingredients without artificial chemical additives. Most brands available for sale are concentrated and require dilution before being applied to the garden. Though initially rather odoriferous, gardeners who use the substance as a fertilizer should be assured the smell fades within two days, according to North Carolina State University Extension.

Fish Emulsion Production

Most fish emulsion products are made by baking, pressing and processing the menhaden fish, an algae-feeding fish which is an important prey food for commercial-grade fish such as mackerel, striped bass and bluefin tuna. A very bony fish, menhaden is valued primarily for its oil, a gallon of which can fetch as much as two times the market rate of petroleum, according to University of Minnesota Extension. Menhaden oil is placed into a centrifuge, and the solid materials which are skimmed off are then boiled down and sold as fish emulsion.

Nutrient Content

Chemical analysis of the nutrient content of fish emulsion vary from brand to brand. Nitrogen content varies widely, with some brands containing as much as 5% or as little as 2 percent nitrogen (N) by weight. Phosphorus (P) content is generally around 2 percent and potassium (K) from 1 to 2 percent. All three nutrients are required for healthy plant growth, flowering and root development. Most types of fish emulsion also contain trace elements of calcium, magnesium, sulfur, chlorine and sodium, all of which are taken up and used by plants in small quantities.

Benefits

Compared to plants grown with no fertilizer at all, applications of diluted solutions of fish emulsion twice a week results in taller, more vigorous tomato and pepper plants, according to a study conducted on seedling transplants by North Carolina State University. Fish emulsion provides similar benefits as other types of fertilizers; its main benefit is that it is one of several organic alternatives to traditional inorganic chemical fertilizers.

Myths

Fish emulsion companies market their products as having additional benefits other than strictly nutritional. These companies claim that fish emulsion, when used frequently and liberally, improves plant vigor, promotes cold and heat resistance, increases seed germination rates, improves disease and pest resistance as well as improves yield and flavor of fruits. Other than improved vigor and growth, these claims have yet to be firmly verified by science.

Warnings

Fish emulsion should always be diluted according to label instructions, as a concentrated application can easily burn the roots and foliage of plants. North Carolina State University researchers also found that applying diluted solutions of fertilizer to foliage of plants neither increases plant vigor nor yields, so fish emulsion as fertilizer should always be applied to the soil for best results.

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About this Author

Michelle Z. Donahue lives in Washington, D.C., and has worked there as a journalist since 2001, when she graduated from Vanderbilt University with a B.A. in English. She first covered politics as a reporter for the weekly Fairfax Times newspaper, then for the daily newswire Canadian Economic Press, where she reported from the U.S. Treasury. Donahue is currently a freelance writer.