Is Fish Oil a Good Fertilizer for the Garden?

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If you have some extra fish oil that you want to put to good use, take a moderate dose every day for omega-3 polyunsaturated fatty acids, or give your dog a little. But for heaven's sake, do not use it in your garden. The trending fertilizer these days does have fishy references, but it's fish emulsion—ground up, left-over fish parts with all oil removed. It provides some nitrogen to your plants, but is it worth the premium cost?

Is Fish Oil a Good Fertilizer for the Garden
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Fish oil won't help your plants, but fish emulsion might. It's a mild, moderate source of nitrogen and can do some good in your garden if you don't mind paying the exorbitant cost.

What is Fish Emulsion?

When everything is removed from fish that can be harvested and sold, including fish oil, some bits and bones remain. These are the raw material used to make most fish emulsion, a type of fertilizer gaining popularity with many gardeners these days. Various companies sell fish emulsion fertilizer as a good source of nitrogen for your plants.

Like sausages and laws, fish emulsion is more appealing if you don't see it made. Scraps of fish detritus are left to rot in warm water, decomposing as the months pass. Then it is broken down with chemicals. The longer it steeps, the thicker the emulsion, which results in a liquid as solid as fish emulsion fertilizer and often requires dilution with water.

What are the Benefits of Fish Emulsion?

Depending on the kind you buy, fish emulsions provide varying amounts of nitrogen along with two essential nutrients, phosphorous and potassium (even if only at 3 percent or less). Fish emulsions sold commercially are usually 5-1-1 or 2-3-1 fertilizers. The numbers indicate the percentage of nitrogen, phosphorous and potassium, respectively.

All liquid fertilizers have the advantage of getting to your plant roots quickly. Diluted fish emulsion passed rapidly into the soil and is readily usable by your plants. Some fish emulsion manufacturers make the claim that the product also contains proteins and oils that will help your plants.

Fishy Claims?

Everyone agrees that organic fertilizer offering moderate amounts of nitrogen is good for your plants. But critics of fish emulsions argue that the fertilizer is overpriced for the amounts of nitrogen you get. Some statistics suggest that it can be 35 times the cost per gram of nitrogen, compared with other organic fertilizers.

Second, there is some doubt about whether your plants can use any large molecules like the proteins and oils found in the liquid fertilizer. Assuming that the fish emulsion contains proteins and oils, they pass into the soil with the liquid. However, they cannot be used by the plants until microbes transform them into small molecules like nitrate and phosphate. That means that proteins and oils from manure are just as useful for this purpose and much less expensive.

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From Alaska to California, from France's Basque Country to Mexico's Pacific Coast, Teo Spengler has dug the soil, planted seeds and helped trees, flowers and veggies thrive. A professional writer and consummate gardener, Spengler has written about home and garden for Gardening Know How, San Francisco Chronicle, Gardening Guide and Go Banking Rates. She earned a BA from U.C. Santa Cruz, a law degree from U.C. Berkeley's Boalt Hall, and an MA and MFA from San Francisco State. She currently divides her life between San Francisco and southwestern France.

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