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Make your own Fish Fertilizer

Updated: Mar 29, 2022

Fish Hydrolysate is a liquid fish fertilizer and simply consists of ground up fish mixed with water. To help break down the fish and prevent it from spoiling, the liquid has to be made more acidic, as most putrefying bacteria will not survive if the pH drops below 4.5. There are different methods of doing this.

You'll need:

Method 1

any parts of any of your local fish

(the fresher the better)


phosphoric acid

(use 75% or 85% acid if you have access to it,

phosphoric acid cleaners are available online,

depending on the concentration you'll have to

adjust the recipe)

PH paper

heavy duty working gloves and safety glasses for working with phosphoric acid

Method 2

any parts of any of your local fish

(the fresher the better)


EM (Effective Microorganisms)

solution with certain types of bacteria and fungi

that's widely used to create an environment that

aids and supports fermentation

you can order this online

PH paper


Use a sharp knife to chop your fish and all its parts into 1 inch size chunks.

This will make it easier to digest in the liquid.

You can also use a blender to chop it even finer - if you don't mind the mess.

For method 1 with phosphoric acid mix the fish 1:1 with water.

About 6% of the 75% acid are added to 100% of volume of the fish and water mix. That means if you measure 1 gallon (16 cups) of fish and water mix, you have to add just a little less than 1 cup of acid. If you end up with higher concentrated acid of 85%, you have to add about 5% acid to the fish liquid.

For method 2 with EM mix fish with water at a ratio of 1:3 . Add 2 tbsp of EM and 2 tbsp of

sugar or molasses per litre of your liquid.

Once you've added all the ingredients, close the lid and put your bucket in a warm place (optimal 25º - 30ºC) though out of the sun if possible as it does attract flies.

And try to stir it throughout the day every 2 - 3 hrs.

A simple contraption would be to hold your drill with a mixer rod attached to it that fits through a hole in the lid. That way you don't have to open your lid every time to stir thoroughly. You can even tape the lid to the bucket to take extra caution to keep the flies out.

If you are doing method 1 with phosphoric acid it should take about 2 - 4 days (around optimal temperature) to digest all the fish parts.

If you are doing method 2 with EM it will take up to 2 weeks for that process.

Now you can strain out any undigested bones or pieces. A colander almost works better than a sieve. You'll end up with a fairly thick, fatty liquid that can smell of fish, a little musky, almost sweet. It should not smell bad.

It's time to measure the PH of your fish liquid. You need to get to a PH of 4 to achieve the acidic state that means you're done and makes your fertilizer shelf stable. Anything above the PH of 5 is too alkaline, and you'd have to add some phosphoric acid to lower the PH.

Or if you're following method 2 with EM try to lower the PH by adding more EM and sugar sources to bend your liquid over into the more acidic state.

Voila - if you've reached a PH of around 4 you have just made your own fish hydrolysate which you can store in a cool dark place for up to 3 years (or maybe longer). Simply pour it into some recycled and washed 1 gallon plastic orange juice or milk jugs.

When applying it to your garden beds or pots - mix it with water at a ratio of 1:10 for soil and 1:50 for foliar application.

For foliar application I tend to water on cloudy days so the sun doesn't burn the leaves.

When watering with the higher concentrate I do rinse with water after the fertilizer application.

If you would like to read more about this please feel free to download this PDF.

130534 Fish Hydrolysate
Download PDF • 4.01MB

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