Fertilization and amendmentsFish Juice Fish Fertilizer bottle
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Have you ever thought of using fish as fertilizer when planting? As strange as it may seem it isn’t uncommon. Using fish as fertilizer for plants has a long history. Fish has been used as fertilizer for at least 10,000 years and was a very important part of the Egyptian farming system. When preparing the soil to plant corn Native Americans would burry fish into the soil. Throughout the growing season, the fish would decompose and continuously feed the plant.

In this article, we will go through some of the basics of fish as fertilizer for plants. We will also look at how you can make it yourself. If you do decide to make it yourself it can be a very smelly process so it may be easier to just buy it if staying on good terms with your neighbours is important. Also, it doesn’t matter what part of the fish you use. From an environmental perspective, it would be better to use the waste produced from locally caught fish from sustainably caught fisheries are used. Rather than taking food suitable for human consumption and using it to make fertilizer.

Types of fish fertilizer

Fish emulsion and fish fertilizer, are often used interchangeably. However, there are many types of fish fertilizers available.

Fish emulsion

Fish emulsion in most cases is made with the waste material from fish. This means the edible part of the fish has been removed. The fish is then ground in a slurry. The oils are removed and the solids are used to make fish meal. The liquid that is left is what it used to make a fish emulsion.

Fish meal

Fish meal is available as either a compressed cake or a loose powder. Fish meal is the dehydrated parts of the fish meat and bone. The benefit of using it in this way is that there is less of a fishy smell and it can be easily worked into the soil.

Fish Emulsion
Fish Meal
Fish Hydrlysate

Fish Hydrolase

Fish hydrolase uses the whole fish or the fish with minimum processing. It doesn’t matter if you use the entire fish or just the waste material after the fish has been cleaned. The edible parts of the fish may be removed but generally, everything else remains

Nutritional benefits of fish fertilizer for plants

Fish has over 60 elements. That’s roughly half of the elements that we have recorded on the periodic table. Most fish fertilizers are in the range of 5-1-1 or 4-2-2. The nitrogen value of the fertilizer (represented by the 5 or 4) is significant but unlike many chemical fertilizers, the quantities of macronutrients (i.e. Nitrogen, phosphorus and potassium) aren’t so high that they will run off without the plants being able to use them.

Fish fertilizer in soil

Unlike synthetic fertilizers, fish fertilizer contains more than just the elements we would expect to feed the plants. Fish fertilizer also has carbohydrates and proteins. These components are much too complex for plants to absorb. These components are an important nutrient source for the soil food web, especially the fungi present in the soil. Therefore, using a fish emulsion can help in the cycling of nutrients through the soil food web in your soil.

Soil Electric conductivity (EC)

Fish emulsion increases the electronic conductivity (EC) in the soil. Most of the nutrients plants use are positively charged. Thus, if your soil is negatively charged it can hold these nutrients better in the soil.

Clay soils already have a high EC and do well at holding the nutrients in the soil. Sometimes too well, actually. Adding fish emulsion won’t improve the EC of clay soil but can help improve the soil structure.

For sandy soils, the increase in EC would be more pronounced. Because sandy soils allow water to go through it so easily you would still need to do amend your soil with compost or some other soil amendment to move it from a sandy soil to a loamy soil. This is to ensure that the fish emulsion will stay in the soil and not just filter through it.

Soil pH

Fish emulsion is a natural way to raise soil pH. It is natural and not as harsh as some pH balancer products (e.g. agricultural lime). Fish emulsion generally works well indoors or in containers in the garden. However, it can be difficult to use it as a soil pH balancer for large areas. If you have a very large area using a calcium additive to your soil may be required.


When discussing fish fertilizers one of the concerns someone might have is mercury. Mercury can accumulate in fish. If the area the fish comes from has high levels of mercury, in the water you could potentially be adding mercury to your soil.

In regenerative agriculture, some plants are used to pull toxins out of the soil. The process of using plants to remediate soil in known phytoremediation. Some plants are very good at pulling toxins out of the soil and store them in their leaves, fruits and bark. This is thought to be a defence mechanism by the plant to defend them from being eaten.

Cucumber, spinach, tomatoes and lettuce are very good at bioaccumulating mercury. The source of your fish and fish emulsion should be taken into consideration when applying it in the garden.

Is fish fertilizer organic?

To make fish fertilizer some companies can use harsh chemicals to process the fish. Your best option is to check your labels when purchasing and look for an organic logo from a certifying body. I should mention though, organic isn’t the same as all-natural. As long as these chemical additives make up less than 1% of the final product they can be labelled organic.

How to make fish hydrosol for plants

If you’re adventurous and interested in making a fish fertilizer at home you can. Here is what you will need to do.

Fish fertilizer Ingredients

Fish Fertilizer process

  1. In a container add 1 part fish to 3 parts water
  2. Add 1 part molasses to 3 parts weight of water and fish
  3. A couple of tablespoons of your microbes (either EM1 or lab)
  4. Let it ferment for about a month
  5. Then strain through a cheesecloth
  6. Store it in a cool dark place

How to apply fish fertilizer

Fish emulsion can be sprayed on their leaves or watered into their soil. If you are using the option above it should be diluted 1 part fish hydrosol to 10 parts water before use. With all homemade gardening mixtures test a small area to make sure there are no adverse effects before applying it to your entire garden.

If you are using a store-bought version always follow the directions on the bottle. Don’t add more than is recommended.

Fish Fertilizer and Epsom salts

Fish fertilizers are generally high in magnesium and sulphur. Adding Epsom salt (which is simply more magnesium and more sulphur) to your fish fertilizer won’t make a difference. You are likely to add too much magnesium and sulphur to your soil by doing this and it isn’t something I would recommend.

Can fish fertilizer burn plants?

If the concentration of Nitrogen in any fertilizer is too high, it can burn plants and fish fertilizer is no exception. Applying a solution of fertilizer that is too strong can burn plants due to its high nitrogen content, no matter how little is used.

What does fish fertilizer do for plants

Fish emulsion is good for plants because it is high in nitrogen. Nitrogen is the most important element for all plants Nitrogen is important to keep leaves green and the plants healthy. The nitrogen in fish fertilizers will help plants thrive Especially leafy greens such as kale, lettuce and spinach.

Because fish emulsion has so many micronutrients it can provide plants with a wide variety of micronutrients you probably didn’t know your plants were

Fish emulsion for houseplants

Yes, you can use fish emulsion for indoor plants but it does have a fishy smell. The homemade version tends to have a more pungent odour than the store-bought version. If you are planning on using it on your indoor plants you may get a fish odour but it does go away fairly quickly. There are also deodorized versions that you can use on your houseplants.
When using any fish fertilizer indoors you don’t have to apply it as often because:

  1. More of the fertilizer will stay in the soil. Because the plants are in containers, the fertilizer will stay closer to the roots. In the outdoors, you would have more of the fertilizer seeping lower and power in the soil.
  2. You don’t have to water your plants as often because they are indoors. The fish fertilizer will be diluted less often and require fewer applications.

Final Thoughts

If your focus in your garden is on living soil you will see a lot of benefits from using fish fertilizers. Unlike synthetic fertilizers, fish fertilizers require microbial activity in the soil to maximize their effectiveness.

Fish fertilizers depend on soil organisms to break them down. This type of fertilizer is most effective in warm, moist soils, which is where soil organisms are active. Because of this, it should not be applied during winter. Its best use will be a few weeks after the last frost if you are in a temperate climate. If you live in the tropics like I do, you can use it year-round.

Now that you know more about fish as fertilizer would this be something you are willing to try? Have you used it before? Feel Free to leave a comment and let us know below.

If you are in Trinidad and Tobago and looking for fish fertilizer we have some from a local business in our online store.

Disclaimer: This post contains affiliate links. Affiliate links are often used to promote certain products and services. These products and services are only promoted because we believe them to be of high quality and that they are beneficial products/services to our readers.  If you purchase these products/services through any affiliate links, Ah-Grow! will earn a commission paid for by the vendor. This is at no additional cost to you.

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