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.
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.
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.
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.
References:
1) Photo Source: Cheryl’s Garden Goodies
Been under the impression this whole time I’m using my FAA as a soil conditioner to feed the microbes. Microbes feed the soil. Soil feeds the plant.
Macro nutrient content of the fish product means nothing to me as I don’t feed my plants any NPK. I feed them soil.
Just a big platter for the microbes to pick from.
Without macronutrients your microbes will die.
Fish is full of mercury and cadmium. Not an organic fertilizer.
Once fermented all fish can be used as fertilizer. Anything good enough for human consumption can be used as organic fertilizer once fermented or composted.
More than 80% of the elements in the periodic table do exist in fish it is a great organic fertilizer if made properly
Just got my own home made fish fertilizer lab tested and this is what I got:
N= 1.7%
P= 0.5%
K= 0.6%
Ca=0.7%
Mg= 0.1%
and a ton of trace elements.
I will give about 50 liters to my plants every day from April to the end of August. Because I am making my own I dont pay a fortune to fish fertilizer.
I am a farmer, I dont want to be a chemist. Synthetic stuff is way too complicated, you need to understand your your negatively and positively charged ions. I used to go synthetic and it did not work for me because I applied magnesium and calcium at the same time, I did not know they were not compatible, and I paid the price. Calcium is extremely important for my fruit quality. My own Fish Fertilizer has both and they are naturally chelated. And my plans can absorb both no problem. I used to apply peters professional products along with top of the line Ca fertilizers, all very expensive stuff. They argue their products have state of the art chelated formulas. Still did not work for me. My leaf analysis were all over the place with synthetic. I find organic farming forgiving and more disease resistant. You can not monkey with chemical stuff but organic fertilizers are very mild so very forgiving.
I understand you are concerned about its price, make your own, it is cheap. 50/50 fish scraps and a cheap sugar source, let it ferment for a few months and you are done.
The whole idea of organic farming is we feed the soil not the plant, you are so hardcoded to the plant uptake, there is a lot more going on in the soil. Study the other side of the medallion, the soil biology…
“you need to understand your your negatively and positively charged ions” – no you don’t.
“magnesium and calcium at the same time, I did not know they were not compatible” – not true – many fertilizers contain both nutrients as do many sources of water.
“The whole idea of organic farming is we feed the soil not the plant” – true – but this also applies to using synthetic fertilizer.
Robert,
80% of the time the reason why something is deficient in the leaf analysis is not because you are lacking that “thing” in your soil, but you have excess of another “thing” in your soil. So when it comes to synthetic stuff you just have to understand your positively and negatively charged ions. Remember no off the shelf fertilizer is complete so you will need to additionally apply something in the form of another thing (ie: magnesium sulphate, ion suplhate, potassium sulphate…etc.
Lets say your leaf analysis says you are deficient in iron, magnesium and/or calcium. Try giving all these at the same time and see what happens. This will inhibit the plant uptake.
Synthetic fertilizers contribute very little to the ecosystem or structure of the soil. They may actually decrease soil fertility due to chemical nitrogen stimulating excessive microorganism growth, which, over time, depletes organic matter in the soil.
incorrect or over application may burn plants due to high concentrations of chemical nutrients, which are salts.
Can cause excess top growth and stress roots.
We have said zillion times if you make your own fish fertilizer it is not expensive. You keep saying that fish fertilizer is mostly water, what is not? Even you are mostly water. People use fish amino acid and fertilizer at the same time and they get great results. Chemical stuff is for the chemists not for the farmers. And I know you are a chemist.
Please stop saying that chemical fertilizers feed the soil. They just dont. They actually disturb the soil. They are not designed to feed the soil but the plants. The bacteria in the soil needs large molecules to breakdown… very different concept. You may know a few things about chemistry and plant uptake but when it comes to biology you have a long way to go.
“80% of the time the reason why something is deficient in the leaf analysis is not because you are lacking that “thing” in your soil, but you have excess of another “thing” in your soil.” – where is the proof that this statement is correct?
You have to understand that magnesium is a nutrient – you do not have to understand it is an ion, or that it has a double positive charge.
“chemical nutrients, which are salts” – all nutrients are salts even if from organic sources – this is basic chemistry.
“fish fertilizer is mostly water, what is not” – synthetic fertilizer and compost
“Chemical stuff is for the chemists not for the farmers” – but most farmers use it???
“chemical fertilizers feed the soil” – I have never said this. Soil is not alive so you can’t feed it. They don’t feed the plants either.
ive used horse manure compost 4 yr old mostly because i have free access to it ive never used fertilizer just compost very light pest problems once the soil is built just cover crop an plant dont have to irrigate any more either .building soil is the answer not fertilizer
Chemical fertilizers do not feed the soil. You should read Elliot Coleman’s books to understand the difference. A soil that is only fed organic matter will be rich in bacterial and mycorrhizal fungi that will reach much farther than the plant can to find needed nutrients. A soil that has a lot of inert chemicals dumped on it will not support the same levels of flora. One advantage of using a fish fertilizer is that it stimulates positive bacterial and fungal activity in the soil. That’s what’s meant by “feeding the soil.”
“Chemical fertilizers do not feed the soil. ” – nothing feeds soil – it is not alive, but fertilizer does add nutrients – the exact same nutrients added by organic material – basic chemistry.
If Coleman says different – I suggest not reading his stuff.
“One advantage of using a fish fertilizer is that it stimulates positive bacterial and fungal activity” – why would it only stimulate “positive” microbes? It will also stimulate pathogens. This is the kind of nonsense that is common in pro organic circles.
“nothing feeds soil – it is not alive” This is incorrect, I use many live soils. Particularly mosses. They are considered soil, and are alive. I don’t grow my Nepenthes in dead Sphagnum. One could then say the moss is just an anchor, but then that’s what soil is.
To further expand, when people talk about “soil” it means the microbiome. This isn’t coming from a pro organic person, I love using synthetics and also do tissue culture, but to flat out say soil is not alive and nothing feeds it is wrong.
“Particularly mosses. They are considered soil,” – no mosses are not soil.
By definition soil is not alive. The soil ecosystem does contain life.
Hi Peter, would you be able to let me know your recipe for liquid fish fertiliser. I was considering using Charlie Carp, but as you said very expensive. I have a beef cattle property only 70 acres. Good volcanic red soil high rainfall. Mainly use Mo single super phosphate, every 3 years. Appreciate your time Regards Myles.
I am not a scientist and know very little about anything you all are speaking of. I can only give you my experience. I am 54 years old. I grew up in South Pasadena, California. My mother was an expert gardener and had beautiful blooms of every kind over our 1 acre property. As well, she had the most big and beautiful hanging plants, and ferns of every kind. She was known, city wide for her rose garden. We had numerous, fruit trees of every kind and a vegetable garden that produced more beautiful, large vegetables and fruits in more abundance than our entire neighborhood could eat. My mother canned the rest which covered every wall of our basement. She made pies year round and gave away and sold her many canned goods, year round, so that she could make room for more. Anyone in our city (not small nor large), knew of my mother’s garden. She very rarely had to deal with pests and diseases in her garden, even her tomatos that were large, beautiful and delicious (though I hate tomatoes). My mother NEVER used any other fertilizer but FISH EMULSION IN GALLONS AND GALLONS. I am not even close to the gardener that my mother was, mainly because our lifestyle, and times, do not allow for gardening 24/7. However, FISH EMULSION has worked for all of my garden and potted plants for years. BOTTOM LINE is that science cannot compare to results! I wouldnt use anything else; WHY? Dont answer because if you read my testimony, you couldnt give me a reason!
1) Nobody said fish fertilizer does not work – that is not the point of the post. If you want to use a very expensive fertilizer go right ahead.
2) Your statement “science cannot compare to results! ” clearly shows that you do not understand how science works. What you are describing is anecdotal results – which mean very little when we are trying to understand the facts. I’ll bet your mom never made properly designed controlled studies? Without them, the observations do not mean very much, except that it worked for her.
https://www.gardenmyths.com/anecdotal-evidence-not-worth-the-screen-its-displayed-on/
Very Interesting how many folks over the years how commented on this post defending Fish Fertilizers. I am a long time market farmer growing fruits and vegetables for retail market. I have trialed various fertilizers side by side. The trials were with similar NPK organic fertilizers. Some manure based from various animals, soy based, meat/blood meal based, fish based and more. Fish based fertilizers always won any of my trials by producing healthier, higher quality, better yielding plants. Yes, I believe Robert is absolutely right the nutrients are the same from any source. But I also believe there are phytonutrients and/or other not studied compounds in fish that contribute to higher performance of this fertilizer source. Whether the plants benefit from these nutrients directly or they benefit the microbes which in turn benefit the plant is unclear. The benefits of phytonutrients on human health is a new and not thoroughly studied/understood topic yet. Certainly could be concluded that nutrition in other life forms is not 100% understood. There is no study proving fish fertilizers have any special properties beyond the mineral nutrients it contains but there is also no study proving it doesn’t either. All we have is a lot of antidotal evidence. Quite a lot it appears when you read the responses to this post.
You need to understand soil biology! plant chemistry and soil biology are not the same, you are talking as if they are the same thing. we organic farmers indirectly feed our plants and conventional ones directly feed their crop. Ours is more sustainable yours is not, our product tastes better more disease resistant than yours, in 50 years you will have dirt in your hands and we still will have soil full of life and ready to go another thousand years.
Chemical fertilizers have extremely high TDS levels, only a fracture of that is being absorbed by the plants, guess where the majority of that stuff is going? Lakes, underground waters, rivers and lower altitude residential areas. Chemical fertilizers not only disturb the soil but also the inner seas and ocean shores. You are turning the world into desert, your kind has been doing this in the last 5 decades, this just has to stop, our soil can only handle a certain amount of salt, yes chemical fertilizers are salt! We want our soil back and you may be happy with the dirt you have. That’s not what we want. Synthetic fertilizers can not be used responsibly because they are salt, and why would someone downgrade to syntactic? There is enough organic source. Make your own fish fertilizer, your own compost, your own kelp fertilizer even your own worm castings, neither more expensive nor more complicated than growing plants. Sorry I will go organic, and you can get all salty and dirty
You missed two critical points in the story.
1) Organic sources decompose to provide the exact same nutrients as synthetic fertilizer. Everything you said about synthetic also applies to organic. You need to understand basic chemistry.
2) This post is not about organic vs synthetic. It is about the fact that fish fertilizer is a very expensive source of organic material – it is mostly water, and it contains very little of the carbon source that is important for soil biology.
“Organic” fertiliser is just as capable of polluting waterways as chemical fertiliser. That’s why we don’t allow septic to leach into water, nor send sewerage straight into the river (if we are clever). The idea that “organic” = “good” is nonsense. I can point to a dozen species of trees that if turned into mulch,the leachate would cause fish deaths in waterways. As for salt contamination, “organic” methods are not risk free either. If you use seaweed as a soil improver you have to remove the salt first- it’s deadly! I use natural mulches and organic materials on my farm everywhere. They work well, as far as they go. But the fact that they are organic does not automatically make,them good or fit for purpose. It’s just not that simple and any suggestion that it is, is just dogmatism. We need to stop relying on rubbery terminology like “organic” and “natural” to understand or promote techniques. What IS useful is understanding plant physiology, soil chemistry, soil ecology. First stop for all of us should be soil and water testing. That might include looking at pathogens. I used lovely, clear dam water to irrigate a crop of parsley. Too bad I didn’t test the water for pathogens- my lovely “natural” water contained fusarium and trashed the parsley. Lucky I didn’t irrigate the bananas with it. My advice is, yes, build up your soil structure and treat it as an ecosystem. But stop using imprecise language to avoid problems or limitations with any particular approch. Understand the processes that create optimum conditions for plant growth and choose methods demonstrated to create these conditions. Forget about the labels.
Fish fertilizer is burn free N. Forget about about the N uptake, it is not your job to feed the plants N, let the soil feed the plants. Burn free N it will not get washed out, who cares about the NPK ratio? it will keep fermenting the soil if used often enough. And if you make your own it is not expensive at all. Beneficial bacteria will get attached to the root system and will keep the plants healthy, can any synthetic fertilizer do this? NPK ratios are BS, they get washed out, what you need is organic burn free stuff multiplying itself and attaching to the root systems
1) What is “burn free N” – there is no such thing really. Organic nitrogen won’t burn plants because it is not in ionic form. But organic N decomposes, release ionic N and then it can burn plants.
2) Burn free N will be washed out of the soil as it is released. It is no different than fertilizer N.
3) “it will keep fermenting the soil if used often enough” – no it won’t – microbes cause fermentation, not nitrogen.
4) “Beneficial bacteria will get attached to the root system and will keep the plants healthy, can any synthetic fertilizer do this?” Bacteria can’t keep plants healthy and provide nutrients if there are no nutrients in the soil. It is the NPK that feeds both the plant and the microbes. And Yes, synthetic fertilizer can keep plants healthy – think about hydroponics – nothing but water and synthetic fertilizer.
5) “NPK ratios are BS” – you really do not understand the whole concept of plant nutrients.
6) “organic burn free stuff multiplying itself” – organic nitrogen sources can’t multiply” themselves.
people rarely ask where the fish by products come from, especially if they ignore toxic farmed fish by products
Plants can take up large molecules, though:
https://www.sciencedirect.com/science/article/pii/S1674205214605499
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6164190/#:~:text=The%20'rhizophagy%20cycle'%20is%20a,a%20free%2Dliving%20soil%20phase.&text=Intracellular%20microbes%20trigger%20formation%20of,they%20exit%20from%20root%20hairs.
From your first link “the importance of organic N uptake for N nutrition and plant performance in different ecosystems is still a topic of debate.”
But I fail to see how this changes the main message and conclusion of my post. Unless you can show studies that demonstrate better plant growth with amino acids, the conclusion remains the same.
I would pick an average organic fertilizer over the best synthetic fertilizer. Why? Simply because organic fertilizers feed the microbes and microbes are 90% water. You should study the “trade” between the microbes and the root systems.
Fish fertilizer if properly fermented one of the best microbe feeders on the face of the earth.
Synthetic fertilizers are toxic to our under ground waters, they make the soil lifeless.
I am not surprised you hold some of these views. They are common myths promoted by some organic gardeners – but that does not make them true.
1) You did not provide any scientific references to support your position.
2) Both organic and synthetic fertilizer feeds microbes – that is why you see an explosion of microbe growth right after applying synthetic fertilizer. The nutrients from both sources are identical.
3) Synthetic fertilizers are not toxic to microbe life. Both types of fertilizer release the identical nutrients.
4) Both types of fertilizer, if applied in excess, will pollute ground water.
This is all explained in more detail in my book on soil: Soil Science for Gardeners.
I agree that the commercial fish emulsion fertilizer may be overpriced for the scientifically not yet quantified benefits.
But I have one point to make, current science might not able to quantify all the nutrients required by plants. NPK plus other trace minerals might be oversimplified. Imagine what a human required nutrients will be, protein, mineral, carbohydrates etc, thats all? is that all human body required? Probably that’s also oversimplified.
So current price might not have scientific support but there might be empirical evidence, probably only commercial farmers might tell the difference?
But if we insists on just comparing the N, then the answer is straightforward.
When comparing plants to animals we find plants don’t normally need a lot more than the basic nutrients – they are better able to make the chemicals they need. Plant roots are also not able to absorb larger molecules so we can be quite sure these are not used by plants. But it is certainly valid to think there might be some small molecule that is of benefit to plants and found in fish fertilizer.
Since plants can grow quite well in simple fertilizer providing the essential nutrients only – that is how hydroponics works – we can be quite sure the plants don’t need these other molecules. That is not to say they might not benefit from their presence. So far science has not found evidence of this.