Can You Turn Fish Waste Into Fertilizer? 7 Facts

Fish waste is not something most people think of when they think of fertilizer. However, some farmers and homesteaders use it as part of a compost pile, which makes it seem like it would also be a good fertilizer.

You can turn fish waste into fertilizer by mixing it with grass clippings, wood chippings, and leaves. You can also add it to the soil directly by blending it up first. When mixed into a compost pile, fish waste can work as a soil amendment and fertilizer.

The rest of this article will discuss some interesting facts about using fish waste as fertilizer. Be sure to read on if you want to learn more!

Things To Know About Turning Fish Waste Into Fertilizer

Turning fish waste into fertilizer is an excellent way to prevent it from being put back into the ocean or in a landfill. But of course, it’s also a great way to help your soil and plants due to the nutrients present in fish. 

Not only can you use the excrement from pet fish as fertilizer, but you can also repurpose leftover components of the fish you cook. There are many benefits of using fish waste in this way, so it’s worth considering. But before you decide to transform your fish waste into fertilizer, it’s essential to learn more about the process.

Below, I’ll discuss some interesting and important things you should know about turning fish waste into fertilizer.

1. Fish Waste Can Be a Soil Amendment and Fertilizer

Although you can blend fish waste and apply it directly to the soil, you can also mix it into a compost pile and use it as a soil amendment. This is easy to do, and you only need a few materials:

  • Blended fish waste
  • Other organic waste (grass, leaves, etc.)

To make fish waste into compost, you need to mix the fish in with things like grass clippings and leaves. It’s vital to turn it regularly to promote airflow. Once you’ve created your compost pile, microorganisms will begin to feed on it, heating it and breaking it down into humus.

Eventually, you’ll be left with a nice pile of nutrient-rich compost soil. When used as compost, it can help amend the soil. So if your soil is too dense and clay-like, this mixture can help loosen it up. Or, if your soil is too sandy and loose, it can help make it denser. 

On top of that, the mixture will act as a fertilizer by adding vital nutrients to the soil. If you want to add nutrients and don’t care about amending the soil, you can simply put the fish waste directly into the ground without composting it.

2. The Foul Odor Goes Away When Composting

You’re probably wondering how bad the smell is when using fish waste during the composting process—that’s a valid question! As you probably know, fish can develop a foul odor pretty quickly. 

With this in mind, you need to be prepared for the initial smell. 

However, the smell eventually goes away due to the decomposing process. As the microorganisms feed on the fish waste and break it down, the scent begins to fade. By the time you use your compost mixture, you likely won’t notice much of an odor at all.

You should still be aware that the smell will be bad initially, so you should keep any compost piles as far away from your home (or other people) as possible. Due to the nature of the pile, it will attract bugs, insects, and rodents, and you certainly don’t want them near you or your home.

Although the smell eventually subsides when composting, it won’t diminish as quickly if you use the fish waste directly in the soil without composting it first.

3. Fish Waste Fertilizer Helps the Environment

Fish waste is terrible for the environment for several reasons. It’s mainly because the waste gets put back into the ocean and causes issues like: 

  • Disease
  • Oxygen blockages
  • Smothering of organisms in the ocean

Therefore, using fish waste as fertilizer helps alleviate some of the negative things that occur in the ocean because less fish waste gets put into the sea.

Plus, the soil benefits greatly from fish waste, which is another reason why it’s great for the environment!

4. Fish Waste Adds Plenty of Nutrients to the Soil

Fish waste is full of nutrients, so you certainly don’t want them to go to waste. Soil and plants thrive when they receive the nutrients they need, and fish fertilizer is an excellent way to provide them with what they need.

Most importantly, fish waste contains the three essential nutrients that benefit plants:

  • Potassium
  • Nitrogen
  • Phosphorus

It’s also an excellent source of other minerals, such as:

  • Zinc. Zinc is essential for soil and plant health, so using fish as a fertilizer is a great way to give the soil this much-needed nutrient.
  • Iron. Iron is another essential nutrient for the maximum health of soil and crops.
  • Magnesium. Magnesium is essential for soil, and fish waste contains plenty of it. 

Although many soils naturally contain some of these minerals, using fish waste as fertilizer ensures that your soil and plants can thrive as much as possible. 

5. You Can Go to Grocery Stores/Markets for Fish Waste

Now that you know more about using fish waste as fertilizer, you may be wondering where you can find fish waste in the first place! If you don’t have any fish waste at home, you can visit your local grocery store (if they sell fresh fish) or a fish market and ask if they have any leftovers.

If they do have waste, you can most likely take it for free; in fact, you’re doing them a favor by taking it. Once you’ve got all the waste you need, you can bring it home and use it.

6. Fish Poop Is Also Good for Plants

While fish waste and leftovers are good for plants, fish poop is also an excellent source of nutrients. This might not surprise you, considering the benefits of other animals’ manure, like cows. 

Of course, many would consider this disgusting and wouldn’t want to use it as fertilizer, but you can try it if you wish. The best way to do it is to collect the poop from your fish tank and add it directly to the soil around your plants.

7. Fish Waste Fertilizer Is Suitable for All Plants

Fish waste fertilizer is not something you can only use for specific plants or certain soil types. No matter where you are or what plants you have, fish will benefit your garden! 

It won’t be beneficial (and might cause issues) if your soil is already packed with nutrients and doesn’t need anything extra. If you’re unsure of whether your soil needs any nutrients or not, you should do a soil test. 

Although fish waste is highly nutritious for the soil, too much of the nutrients can harm your plants. However, this isn’t specific to fish waste fertilizer. Any fertilizer will be bad for your plants if your soil already has enough nutrients.

Once you know what your soil needs, you can be sure that fish waste will be nothing but valuable and beneficial.

How To Make Fish Fertilizer

I’ve already briefly discussed how to make fish waste compost, but I haven’t talked about how to make a fish emulsion fertilizer. There are two great ways to use fish in the soil. You can either blend it and apply it directly to the soil or create an emulsion.

In this instance, I’ll explain how you can create your own fish fertilizer by making an emulsion.

  1. Mix fish waste with organic waste. A popular example of organic waste would be grass clippings.
  2. Add in molasses (this is optional).
  3. Add water to the mixture.
  4. Leave it to sit for a few weeks (two at least).
  5. Check on the mixture weekly and mix it each time you check on it.
  6. Once ready, you can drain it into a container. The liquid that drains out is the emulsion you can use in your garden.

Before using your homemade fish emulsion, you will need to mix it with water to dilute it. The best time to use this fertilizer is during the growing season. To learn more about the best time to fertilize plants, check out this article.

If using fish emulsion fertilizer, you can apply it every 3-4 weeks during the season.


You can turn fish waste into fertilizer because it’s highly nutritious and beneficial for soil and plants. Fish waste contains nitrogen and potassium, which are vital for plant health. It also has other nutrients that are helpful to the soil.

There are different ways to use fish waste as fertilizer. You can add it to a compost pile to create a fertilizer and soil amendment. Alternatively, you can put fish directly into the soil or create an emulsion.

Fish waste is organic, meaning it’s free from harmful and unnecessary chemicals. Additionally, it’s suitable for all plant and soil types!

If you want to learn how to make homemade fish fertilizer, you can read my other article here: How to Make Homemade Fish Fertilizer (DIY Guide)

Alexander Picot

Alexander Picot is the principal creator of, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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