Fish Emulsion

We’ve all heard about fish emulsion, but what’s really in it and how does it actually work in the garden?

Before writing this post, I had always thought that fish emulsion was, well, fish poop. I was wrong. Fish emulsion is actually the mashed up leftovers from fish processing plants - sort of a fish mojito for plants. Ew, sorry.

Proponents claim that fish emulsion is an excellent slow-release fertilizer, especially for delicate seedlings, providing a gentle dose of nitrogen. Fish emulsion is organic and nontoxic.

Some of the down sides of using fish emulsion are cost and smell. Let’s face it, dead fish have a pretty short half-life. The smell may also attract some unwanted wildlife, such as skunks and flies. Some fish emulsion manufacturers claim that their product is “non-odorous”. I can’t imagine how that happens, but maybe.

Now, most commercially available fertilizers range in significantly higher numbers than fish emulsion, when it comes to nutrients. If you recall, the NPK numbers found on fertilizer packaging refers to the percentage by weight of nitrogen, phosphorous, and potassium, respectively. Commonly, the nitrogen and potassium numbers will be in the double digits, while phosphorus is usually a single digit number. For fish emulsion, the numbers are much lower. The NPK ratio of fish emulsion ranges from 4-1-1 to 5-2-2. This is neither good nor bad, it simply shows that the nutritional value of fish emulsion is lower than many other sources of plant food.

The science behind fish emulsion studies has come to some specific conclusions:

• While some gardeners claim that soaking seeds in fish emulsion will increase germination rates, scientific research has shown that this is not true.
• Transplanted tomatoes and peppers drenched with 1/2 ounce of fish emulsion per gallon of water grew bigger than all of the other plants in one study.
• Studies on the use of foliar (leaf) sprays of fish emulsion showed no significant difference between sprayed and unsprayed plants.
• In a study using fish emulsion, combined with humic acid, on a soybean crop, yields were not impacted by the fish emulsion.

So, the bottom line on fish emulsion: it is an effective way to feed delicate seedlings and transplants, providing easy to use nutrients, but it doesn’t do much of anything for larger, more mature plants. 

In my book, I categorize fish emulsion as a plant baby food.