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How to Make Fish Scale Fertilizer

How to Make Fish Scale Fertilizer

People have been using fish byproducts, such as fish scales and bones, as fertilizer for centuries. Native Americans used to put small fish in tilled soil before planting their seeds; these small fish decomposed slowly, thereby releasing small amounts of nutrients to the plants as they grow. Today, fish waste is usually incorporated in fertilizer; if you read carefully, you may find the ingredients in your bag of fertilizer probably contain 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. Fish scales and byproducts can actually be used as fertilizer in two ways: First, as a slow-release fertilizer, and second, as a quick release fertilizer. 

How to Make Slow Release Fish Scale Fertilizer

This is probably the easier of the two fishy fertilizers to make. It skips the fermentation process and adds the fish mulch directly to your plants’ soil, allowing it to decompose naturally and slowly over time.

To make this fertilizer:

  1. Gather your fish byproducts and emulsify in your food processor to mulch.
  2. Take small amounts of this mulch and work it directly into your garden’s soil, making sure to cover the mulch completely with a layer of soil to cover 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 it requires 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 disturb not only 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 fermenting the fish byproducts to release the nutrients and diminish the smell.

How to Make Quick Release Fish Scale Fertilizer

Since fish scales do not contain high amounts of all the essential nutrients plants need, home composters often add other ingredients to offer a complete source of nutrients to the plants.

Below is a systematic guide on making quick-release fish scale fertilizer and what to add for additional nutrition:

  1. The first thing you would want to do is gather all the necessary ingredients you want to add to your fish scale fertilizer. Fish scales, bones, organs, and any leftovers you want to get rid of are 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.
  2. 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.
  3. To create your composting mix, add the fish waste to equal amounts of leaf litter, your molasses, and seaweed.
  4. Fill a container three-quarters of the way with the compost mix and then top it off with water.
  5. 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.
  6. Once ready, pour off the liquid. This liquid is your fish scale fertilizer, and you can use it in the 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.
  7. Whatever is leftover 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 Available from Fish Scales

You will see that most fertilizers contain a high ratio of Potassium, Nitrogen, and Phosphorus, which is why fish byproducts 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 Encyclopedia.


Potassium plays an 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, regulating 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.


Like Nitrogen, Phosphorus plays an important part in the production of energy, or ATP, through converting the sun’s 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.

Final Thoughts

So, next time you have leftover fish scales and bones and have no idea what to do with them, consider converting them into nutritious fertilizer for your plants!