People have been using fish waste and by products as fertilizer for centuries. There are even stories of Native Americans who used to put small fish in the stilled soil before thy planted their seeds. These small fish decomposed slowly, thereby releasing small amounts of nutrients to the plants as they grow.

This makes a lot of sense, especially for fish scales and bones, which make up the majority of the waste from the fish industry. Commercially, fish waste is also incorporated in fertilizer if you read carefully, you should find the ingredients in your bag of fertilizer probably contains some kind of fish byproduct.

Making your own fish scale fertilizer is just one-step away from having your own compost heap, and even though you can add fish waste to your outdoor composting system, it may be best used on its own. So if you are considering making your own fish scale fertilizer, here is what you will need to do.

Fish mulch contains Potassium, Nitrogen and Phosphorus, which are vital elements for plant growth and reproduction. To make your own fish scale fertilizer, create a compost mix by mixing equal parts of fish waste with organic matter in a large container. Add some water and cover with a lid. Allow this mixture to ferment in a dark place for several weeks. Once ready, pour off the liquid and use diluted to fertilize your soil.

Fish scales and by products can actually be used as fertilizer in two ways. Firstly, as a slow release fertilizer and secondly as a quick release fertilizer, both with their own advantages and disadvantages.  Let’s have a look at these in dome more detail.

Slow release Fish Scale Fertilizer: a Step by Step Guide

This is probably the easier method of the two but is has some distinct drawbacks in terms of smell. This method skips the fermentation process and adds the fish mulch directly to the soil of your plants, allowing it to decompose naturally and slowly over time.

  1. Gather your fish by products and emulsify in your food processor to mulch.
  2. Take small amounts of this mulch and work directly into the soil of your garden, making sure to cover the mulch completely with a layer of soil to cover the most of the smell.
  3. Water the soil well to allow decomposition and slow release of the nutrients from the fish scales.

This method has the advantage in that is less hands on work, and it attracts a diverse variety of microorganisms in your soil, thereby improving its overall condition.

The disadvantage of this method is obviously the smell of the decomposing fish, which may leave a stench in your garden that will not only disturb you, but also your neighbors! This smell could also attract some unwanted visitors, depending on where you live.

This is why most gardeners believe in first fermenting the fish by-products to release the nutrients and to diminish the smell.

Quick Release Fish Scale Fertilizer: a Systematic Guide

Since fish scales by itself does not contain high amounts of all the essential nutrients plants need, home composters often add other ingredients to offer a more complete source of nutrients to the plants. Below is a systematic guide on making fish scale fertilizer and what to add for additional nutrition. This guide was adapted from The Grow Network community

  1. The first thing you would want to do is to gather all the necessary ingredients you want to add to your fish scale fertilizer. Fish scales, bones, organs and any leftovers that you want to get rid of, is great to include.

Some gardeners add in seaweed and molasses to increase the nutrient factor. Along with some leaf litter from your garden, you should have a good nutritional mix for your fertilizer.

  • Now take the fish waste and purify it in your food processor. This is a very smelly process, but it luckily washes right off with soap. The reason for doing this is that this will release the nutrients from the harder parts such as the bones and scales much quicker, than simply leaving it to decay on its own.
  • To create your composting mix, add the fish waste to equal amounts of leaf litter, your molasses and seaweed.
  • Fill a container three-quarters of the way with the compost mix and then top it off with water.
  • Leave this mixture covered and out of direct sunlight for several weeks. Make sure to stir the mixture every few days to keep the organic matter and microorganisms equally distributed.
  • Once ready, pour off the liquid. This liquid is your fish scale fertilizer and you can use it in diluted form either by adding to the soil of your plants, or by spraying on the leaves. A good dilution ratio is 1:12 of fertilizer to water.
  • Whatever is left over in the bin after you poured off the liquid fertilizer can then be used to ferment another batch of fish scale fertilizer by adding more water, or you can simply throw the leftovers into your normal composting system.

Plant nutrients from fish scales

You will see that most fertilizers contain a high ration of Potassium, Nitrogen and Phosphorus, which is why fish by products make such great fertilizer. Below is some basic information on why these elements are important for plants and what their deficiency symptoms are. For more detailed information, you can visit


Potassium plays and important part in plant metabolism, photosynthesis and disease resistance. More specifically, it allows the plants to take up CO2 and enables the production of ATP, a molecule that distributes energy throughout the plant.

The plant’s water balance is also affected by potassium, as it regulates uptake and evaporation from the leaves. Potassium also affects plant growth as it plays an important part in protein and starch synthesis.

Deficiency symptoms include brown discoloration and scorching of the leaf tips as well as yellowing or other discoloration of the leaf veins. In some plants, purple spots appear on the underside of leaves and in most cases, growth is stunted.


Nitrogen is a major component of chlorophyll, the powerhouse of a plant’s energy production. The chlorophyll enables the plant to make sugars from CO2, minerals, sunlight and water, which keep the plant alive and growing. Chlorophyll is also what makes a plant green.

Lastly, Nitrogen is an important part of all amino acids, and without it, the plant cannot grow and reproduce. Deficiency symptoms include the yellowing of leaves as not enough chlorophyll can be produced. Plants will also stop reproducing and have stunted growth from a Nitrogen deficiency.


Just like Nitrogen, Phosphorus plays and important part in the production of energy, or ATP, through conversion of the suns energy to sugar compounds in the leaves. It is also an important element in the structure of DNA, and therefore affects growth and reproduction in plants.

Deficiency symptoms in plants are usually seen in stunted growth and lack of or poor seed formation. Stems are usually spindly and weak in some cases, while older leaves may turn a dark bluish-green.

When a plant starts to show symptoms of a Phosphorus deficiency, it may already be too late to recover, so it is important to make sure your plants always get enough of this nutrient.

I hope you enjoyed this post. Have you used fish products in your composting? Let us know in the comments below.