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 plant’s point of view is minor, but if you are trying to sell product, there are big differences.
Fish emulsion and fish hydrolysate start with dead fish. In some cases this is leftover bits from the fish industry, and in other cases, this is whole fish specifically caught to make fertilizer. 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 are 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 and 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, 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 Its 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
Hi everyone,
I have just collect 10 kg of fish (koi) poop from my koi pond. Appreciate if you can help on the following to use it as a fertilizer for plants.
1) at one point i felt that i had too much fish poop and went a little crazy and pour about 2 cups each into my potted fruit plants, lemon, banana, fig, lime and other plants. around the home. Is this too much? Will i burn the plants with fish poop? Should i remove some?
2) i am now drying the remaining fish poop in the sun. When its dry i would imagine that it can be stored as a powder. How much to apply each time to potted plants? 2 table spoon per week?
3) and there a recommended way and how much fish poop to use as a fertizer? Better to use it dry or mix in water before you water your plants?
4) What is the NPK and other good stuff in fish poop? Would be keen to know.
Much appreciated on any info. Many thanks.
Is this safe for consumption of animals though?
What? It is not made for animal consumption.
I am a farmer from Turkey. What I would tell you is simple:
We farmers are NOT in the business of feeding the plants but the soil. It is the soil’s job to feed the plants. If your soil is full of good bacteria then it is full of life. This kind of soil will support any plant. Fish fertilizer therefore is a great microb feeder in the dirt.
Healty dirt=Healthy plants.
If you spoon feed your plants and ignore the soil health you are a greengrocer not a farmer. Hope this helps.
1. Improve soil structure, improve soil water retention and fertilizer retention, alleviate soil compaction, acidification and salinization, and improve soil permeability
2. Supplement soil organic matter, fertilize soil, activate soil solidification elements, and improve fertilizer efficiency
3. Improve the root system beneficial microbial ecological environment. Promotes hairy root hair growth, root growth and development
4. Activate the endogenous biological enzyme activity of the crop, adjust physiological functions, and improve crop stress resistance (resistance to low temperature freezing damage, drought high temperature and fertilizer damage)
5. Improve chlorophyll content, promote photosynthesis, prevent physiological yellowing and abnormal symptoms of premature aging of crops
6. Promote flower bud differentiation, improve flower bud development ability, preserve flowers and preserve fruit
7. Regulate the respiration of crops, promote the accumulation of soluble solids, promote the uniformity of fruit enlargement, high gloss, increase sugar content, and improve quality.
Good stuff! So, should I be throwing my salmon scales (cooked, usu. in olive oil with the flesh) into my cold, slow-acting compost heap? Thanks.
why not? It might attract rodents.
this is not a comment but a question. Can kudzu be made into feterlizer or do you risk just spreading the kudzu?
Once it is decomposed, it can’t spread.
You must ensure the seeds are completely broken down. That’s basic Biosecurity. I wouldn’t use it- the risks are too high. Pea straw or other legume wastes would be a good substitute.
You guys been talking about this for 2 1/2 years. I believe Robert is qualified to reveal the truth about fish fertilizer. In 1978, I was putting Sargents tick and flea powder on my dog. My neighbor, a professionial nurseryman, walked up and started laughing. He said, “you must know that Sevin Dust and that powder is the same product. I was amazed. Since I had a bag of Sevin Dust, we checked the ingredients and they were exact. Flea Powder (5 oz. for about $4.00), Sevin Dust $1.00 for 3 lbs.)
I believe this is and was Robert’s point. Thank you Robert for your help!
I don’t know about the rest of you, but I have never purchased Tick and Flea powder for any dog.
These are valid points you state. I personally like to use liquid fertilizer once I have mulched my flower beds for the season from an aesthetics perspective since I can easily mix it into a watering can to feed. There is no residue or anything to affect the finished look. Beyond fish fertilizer specifically, other ‘liquid’ fertilizers I have seen are comparable in price. ‘expensive’ is relative and really depends on the size of your gardens. If you don’t have a lot of plants to feed, spending $15 on a bottle of fish fertilizer that will last you the season is not really breaking the bank.
But you could buy the same amount of soluble fertilizer for $1 and have less effect on the environment with less shipping.
I found the article interesting informative but also there’s needs to be a Clarification
I produce 2000 gallons of fish fertilizer a year yes it’s a cold process
For my fruiting trees and bushes I do it because it’s too expensive to purchase my semi homemade version is A little bit stronger With more trace minerals than store purchased
Simply water sugar and milk is allowed to ferment in a 300 gallon tank for one week before fish is added
I get my fish scraps from A fish market 100 pounds a day during the summer it’s the bones the cartilage the skin scales heads crab and shrimp shells All the undesirable parts of the fish are the most desirable parts for Fish fertilizer that’s where all the nutrients And minerals are I wouldn’t take a truckload of salmon fillets for free!
at the end of three month process all the bones and the scales have dissolved adding the extra nutrients into my very standard fish fertilizer formula
When the tank is ready all the fish oil floats to the top just like oil in a pot of water I strain it off and Discard
If you’re purchasing Liquid fish fertilizer you would notice the oil if any it will settle at the top I agree with the article discard it I just pouring it out although I’ve never seen any in store purchased fertilizers
if need to speed up the process
I’ll add extra sugar to my tanks about 35 to 45 pounds of sugar per 300 gallon tank The sugar feeds the bacteria that breaks down the fish in the end there’s no sugar left
The reason why I go through all this trouble Is that I’m after the minerals! I don’t care about NPK Although I take it into account when I’m doing my formula for the year.
I’m not that computer savvy can’t figure out how to attach a photograph of my fermenting tanks
Josh
Human urine is very high in a good organic nitrogen…actually it is a COMPLETE fertilizer
It is not a complete fertilizer: “Urine contains 0.9% urea, or about 0.4% nitrogen. It also contains 0.1% potassium, so it’s fertilizer numbers are 0.4 – 0 – 0.1. Unfortunately it also contains 0.2% sodium which can be toxic to plants.”
From: https://www.gardenmyths.com/the-full-scoop-on-composting-poop/