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Using Fish Food as Plant Fertilizer: Is it Worth it?

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Fish food as fertilizer may seem unorthodox, but using leftover or expired fish food from your fish tanks may be a good alternative to using normal fertilizer for plants since it also contains nutrients for plants.

Fish food contains an array of nutrients and proteins. These nutrients can also be useful to plants as a fertilizer. Fish food doesn?t directly provide nutrients to the plants, but by secondary action whereby bacteria firstly breaks down the fish food into the available nutrients for plants to use.

Fish food, not to be confused with Fish fertilizers (commercial fish by-products that are dedicated for use as fertilizers), is used to feed fishes in fish tanks and aquariums.?

If there is an excess of fish food or it has reached its expiry date, using the fish food as a plant fertilizer may be a good option because of the ingredients it contains. One of the primary ingredients is proteins, which most fish food has between 30 to 45%.

But how would plants use this protein? Would it smell? And would it attract any unwanted guests to your plants? 

I wrote this article because I bought a bag of fish food for my fish. The bag only got to half before it expired. I saw It contained 45% protein and other ingredients that may be useful to plants. So I did some research and found that fish is used as fertilizers for plants. I used it, and this is what I found.

If you want a slow-release fertilizer that will ensure your plant grows healthy for a long time with minimal intervention, I recommend Osmocote Smart-Release Plant Food.

Osmocoat fertilizer

Using Expired Fish Food as Fertilizer

fish food as plant fertilizer

When fish food passes the expiration date, it doesn’t mean that the food is not good again. The expired date is a marker showing that it is not recommended for its primary use after the marked date has passed.

Fish food contains proteins, fibers, fats, and vitamins, along with a number of other additives and preservatives meant to ensure the food does not smell and has a long shelf life. This is crucial since we’re dealing with an unrefrigerated protein product.

How do these ingredients help plants?

It doesn’t! 

Adding fish food to the soil will not directly benefit the plant. Instead, once incorporated properly with the soil, bacteria and microbes will have a field day breaking down and processing the proteins contained in the fish food.

Proteins are organic compounds made primarily of nitrogen and hydrogen with some carbon and oxygen. 

Protein compound

The proteins in the soil are broken down by microorganisms to produce carbon dioxide (CO2), energy, water, plant nutrients, and resynthesized organic carbon compounds such as nitrogen.

Microorganisms play a vital role in keeping the soil in a healthy state for plants to grow.

Soil life plays a major role in many natural processes that determine nutrient and water availability for agricultural productivity. The primary activities of all living organisms are growing and reproducing. By-products from growing roots and plant residues feed soil organisms. Source.

Nitrogen’s primary role in plant development is to help produce healthy, green, flourishing leaves since it is a major component of chlorophyll.

The fish food would, therefore, help add an essential source of nitrogen to the soil for plants to grow.

Would the Fish Food smell?

Fish food has a characteristic smell of fish since the products used to manufacture the fish food is from the byproducts of fish. 

Is smell a factor to consider when using fish food as a fertilizer for plants?

In order for the fish food not to give off that fishy odor, it is known that you will have to incorporate the food 2 to 4 inches into the soil and, in some cases, bury the food under the soil to prevent the smell from creating a noticeable distraction in your home.

Apart from the fishy odor, the breaking down of the proteins will also release some smelly gases such as H2S (hydrogen sulfide gas), which is a typical byproduct of protein synthesis.

For these reasons, fish food from your fish tank should be applied to plants grown outdoors and in the garden.

Using fish food on indoor plants may not be such a good idea since the smell will get unbearable fast! However using aquarium water on plants can have direct benefits, without the smell.

fish food as fertilizer

Will the Fish Food Attract Unwanted Animals?

Due to the protein content and other additives, the fish food will attract ants and other animals such as dogs and cats.

This may not be such a good thing since the dogs will dig directly into the soil, uprooting the plants and while trying to get to that buried bone. Or at least what he thought would have been a bone.

The result would be two things –

  1. The plants will get damaged 
  2. The dogs or cats would get poisoned from eating the potted soil mixture.

It is best to discourage dogs from eating potting soil. Potting soil is specially formulated soil that contains ingredients made for plants with specific needs when grown in pots or containers. The constituents of potting soil are dangerous to dogs and cause a variety of ailments when ingested.?

Therefore, try to avoid areas where using fish food as a plant fertilizer is in close proximity to pets and other wild animals.

Fish Food Vs Fish Fertilizer

Fish Food and fish fertilizer are created from the similar byproducts of fish and other aquatic animals. 

Fish fertilizers offer a source of burn-free nitrogen, along with the other primary nutrients. Which is the same with fish food.

Fish food and fish fertilizers differ from each other as the plant fertilizer directly feeds the plant while the cat food has to firstly be broken down before the nutrients are available for the plant,

This creates a slow release of beneficial nutrients for the plants rather than shocking it with nutrient-rich doses, as with regular fertilizers, which poses the risk of burning the plant. (Fertilizer burn)

When applying water to my plants, I use a cost-effective and durable watering can that I got on Amazon, which makes watering fun and easy without any spillage. 

MyLifeUNIT Plastic Watering Can

How to Apply the Fish Food to the Soil

Applying fish food to the soil the right way is important in preventing unwanted animals from eating the soil and digging up the plants.

The fish food should be mixed in 2 to 4 inches with topsoil first before adding it to your plant pots or garden plants.

This helps lower the odors presented by the fish food and also helps the bacteria to access the food sooner.

After addition, the soil should be watered lightly and allowed to rest. The water would cause the fish food to expand and break down faster.?

Another method is to add water to the fish food which would cause it to expand and break up before mixing it into the soil.

This would also increase the rate at which the bacteria break down the food into beneficial nitrogen for the plants.

The Takeaway 

Fish food is a good alternative to regular fertilizer since it adds a slow release of beneficial nitrogen and other nutrients for plants to grow.

Some consideration for pets and other wild animals should be taken when adding the fertilizer to the soil and it should be done in areas away from pets.

Adding fish food to the soil should be done such that the food is broken up and totally mixed in with a soil mixture before it is added to your plants to help the breakdown of the food and lower the potential smell that comes with fish food.

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