Fish Fertilizer – Is it Worth Buying?

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Robert Pavlis

Fish fertilizer is very popular. It is reported to be a good source of nutrients and a good source of proteins, amino acids and oils – for your plants. Can plants use fish proteins and oils? Is fish fertilizer a good source of nutrients?

Before I go any further let me say that there is nothing wrong with using fish fertilizer. It will help make your plants grow. I have two problems with fish fertilizer; it is extremely expensive compared to other sources of fertilizer and many of the claims for it have no basis.

making fish fertilizer
Making fish fertilizer

Fish Emulsion vs Fish Hydrolysate

What is the difference between fish emulsion and fish hydrolysate? The difference from a plants point of view is minor, but if you are trying to sell product–there are big differences.

Fish emulsion and fish hydrolysate start with the left over bits from the fish industry–the parts no one else wants. These are then treated with various chemicals and enzymes to break down larger organic molecules into nutrients and other small organic molecules. Further treatment can take one of two paths; it is either heated or cold processed. Fish emulsion is the end product if the heating process is used. Fish hydrolysate is the result of using cold processing.

Food Science for Gardeners, by Robert Pavlis

There is great debate between the benefits of emulsion vs hydrolysate–which is better? The reality is that plants can’t use most of the large or even small organic molecules from either process. Normally microbes in the soil degrade these to nutrients plants can use. So the argument that heat in the emulsion process is detrimental, makes no sense. it is true that heat will denature proteins, but they need to be denatured for the plants to use them.

I think the arguments for or against either process is just marketing hype. I have seen no scientific evidence to support the superiority of either process.

Fish Fertilizer Benefits

Fish fertilizer is an organic product–for the most part. So it does have the benefits other organic soil additives have. It feeds plants, microbes and improves soil structure.

But proponents of fish fertilizer make claims that do not apply to other organic fertilizers. Most seem to be centered around the fact that the liquid fertilizer contains proteins and oils. We all know fish oils are very important for our health and so they must be good for plants, right? Wrong!

Plants can’t make use of large molecules such as oils and proteins; see Organic Fertilizer – What is it’s Real Value? for more details. When these molecules are added to soil, microbes digest them and turn them into small molecules like nitrate, and phosphate. It is only then that plants can make use of these molecules.

Since the large molecules need to be degraded before plants can use them, there is little difference – to the plant – between proteins and oils from fish, cows (manure), or even plants. I have found no support for the claim that fish fertilizer is better than any other organic fertilizer.

Soil Science for Gardeners book by Robert Pavlis

The main thing plants need from fertilizer is a source of nitrogen. Garden soils usually have enough P and K and the other minor nutrients. Nitrogen is the thing that is missing in soils. Given this fact, fish fertilizer is no better or worse than other types of fertilizer.

Fish fertilizer has about 2% nitrogen, which is the same as most organic fertilizers; compost, manure, and coffee grounds.

Is Fish Fertilizer Organic?

This probably seems like a dumb question–fish are organic so why would fish extracts not be organic? Here’s why. In the process of turning fish scraps into fertilizer companies add a number of chemicals, including phosphoric acid, and odor inhibitors. Apparently, as long as these ingredients form less than 1% of the finished product, the product can still be called organic. Who knew–organic fertilizer only needs to be 99% organic!

Cost of Nitrogen

I checked several fish fertilizers and a common analysis is 2-4-2 and if you buy in large containers you can get 9 lb (3.8 Kg) for $25. Small quantities are even more expensive. This fertilizer has 2% nitrogen, and so the cost for the nitrogen is $33 for 100 g of nitrogen. Wow! Even fresh caught Atlantic salmon doesn’t cost that much!!

What is the cost of 100 g of nitrogen if you buy a commercial fertilizer? Scotts sells a 30-0-9 at $17 for 6.2 Kg, or $0.91 for 100 g.

Fish fertilizer is 35 times more expensive than commercial fertilizer and plants can’t tell the difference between the two sources of nitrogen.

I can hear your objection – BUT … fish fertilizer is organic. That is true, and organic fertilizers do more than just provide nutrients. They also help build better soil by feeding microbes. Fish fertilizer is about 14% protein which is the same as manure. A 30 lb bag of manure will cost you $4 compared to $75 for the same amount of fish protein. Manure bought in bulk is even cheaper.

I really can’t think of any good reason to buy fish fertilizer if other sources of fertilizer are available.


1) Photo Source: Cheryl’s Garden Goodies

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

243 thoughts on “Fish Fertilizer – Is it Worth Buying?”

  1. Fish Emulsion is actually cheaper than some of the other products I buy, such as Fox Farm and Roots Organics products. The Fish Sh!t beneficial bacteria product I use is $50 for a less than a quart of it. For can buy a quart of Alaska Fish Emulsion. Granted, Fish Sh!t and Alaska Fish Emulsion are completely different products, but what I’m saying is that Fish Emulsion for me is one of the cheapest fertilizers that I use.

    Compared to other organic nutrient products I feel the main advantage to Fish Emulsion is the fast-acting nature of it. Most organic fertilizers release slowly which you have covered in another article, so I’m preaching to the choir on this point.

    I make decent money at my job and some of the plants I grow are very lucrative – my cannabis plants can generate over $1000 per plant, so for me the price tag of Fish Emulsion is irrelevant. Other growers with smaller budgets might not like the price tag. However, just because you want to harness the power of Fish doesn’t mean you need to buy anything. I used to volunteer at a pig farm and the farmer there told me his grandfather always threw Fish in thr planting hole under the plant. Even that will work, although personally I would prefer it in liquid form. There are recipes for making your own Fish Emulsion easily available online. If you already own a fishing pole then you really don’t need to buy anything. You can just catch some fish and make your own if you want to save money.

    • When I farmed avocados in CA. I was looking for a fertilizer that would give the highest pounds per acre. My farm advisor told me about a grower in Santa Barbara who only used fish and kelp in his orchard and averaged 10k pounds per acre, when the county average was 5k pounds per acre. Somehow he figured out how to overcome the clogging problem for the orchard irrigation emitters and got an orchard of healthy and productive trees.

  2. Read the article. Read the comments (took awhile). But it all boils down to whether or not fish fertilizer works.

    I have 26 raised beds here in S. VA where the soil is compacted clay – hence, raised beds. Nowhere within 50 miles can I get good topsoil – it’s all junk. For 4 years my crops have been mediocre at best, even with compost (I always have 3 piles in various stages of cooking)

    I grow peas, beans, beets, okra, tomatoes, potatoes, various lettuces, spinach & pak choi.

    Two years ago I tested FF on 13 of my beds. It was the only thing I did different. The other 13 beds were my “control group”. Both groups of beds were identical in what was planted. I do not spray – direct pour to the soil (don’t wanna be tasting rotted fish when I eat the produce)

    The FF group was bigger, healthier looking, more productive by a country mile – especially the tomatoes.

    This year, I used FF on all beds, and I have already had the best “first plant” crop ever. Getting ready for the “fall” planting that begins soon.

    All I care about is results. And my results speak for themselves. Y’all can say whatever you want – it works for me.

    • It is a known fact that adding nutrients to soil will grow better plants that was never in doubt. It is just that fish fertilizer is a very expensive way to grow plants.

      • I think that what is missing is a discussion about how concentrated FF is in polysaccharides which feed microbes and enhance nutrient turn over. The only other more polysaccharide rich amendment would be aloe which is even more expensive.

        • polysaccharides are starches and sugars. There are much cheaper forms of these if you feel they are needed.

          Unless you add significant amounts – much more than in fish fertilizer, they don’t do much for soil. Molasses for Plants

  3. I have been using fish emulsion as a boost only to vegetable plants that appear nitrogen deficient. (I also generally top off beds with an inch or so of compost between crops.) Is there a less expensive organic “nitrogen booster” that can be applied in liquid form?


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