Fish Fertilizer Preparation

This week in the Flog:

  • Making Fish Fertilizer
  • Photos to go with the recipe!

Some time ago I finally ran out of the fish fertilizer I made last year. Time for a new batch! I documented the process for all those interested in seeing this awesome recipe in action!

Homemade fish fertilizer is an organic fertilizing solution that allows you to move away from petroleum-based commercial fertilizer. It is made from fish which is one of the very best sources of macro- and micro-nutrients for healthy growing plants. You can make it yourself with very limited resources. And it is SCENTLESS. We have an awesome recipe on how to make it here.

In my current living situation, I don’t have the time or space to get a good source of fish waste and make the recipe that way, so I’m just buying a tilapia from the market to use. It’s a nice size fish, and using the whole fish means the end product will be that much better:

fish fertilizer - tilapia

Whole tilapia from the market, guts included.

Now the bloody work. I’m chopping the fish up into smaller pieces and then into the blender they go. This is a pretty messy process and I would encourage you to do it *outside*.

fish fertilizer - chopped fish

The fish gets chopped up and added to the blender

Now before I blend up the fish, I’m going to add the water and sugar. The fish is a little thick to blend on it’s own so I add the water before blending – and adding the sugar now allows the blending to help dissolve it. I’m adding 1L of water, a little less than what our recipe calls for but no matter, there is no real right or wrong here. I’m also adding 150g of sugar – 1/3rd part sugar to tilapia.

fish fertilizer - adding water/sugar

We add the water and sugar before blending to make the blending step easier

Now this whole mixture gets blended up really well. Only takes about 5 minutes or so of blending/pureeing.. My cheap blender has a little trouble with the bones at first but after awhile it’s pretty well blended. Check out the blended goop:

fish fertilizer - blended fish

After blending, the fish fertilizer is very thick and uniform in color

Last step – add the lacto. I’m adding 2 tbsp of dilute lacto serum – there is no rule here, I could have added more or less no problem. But 2 tbsp for this amount of mix is about right in my book, maybe a little on the heavy side which I like.

Now I just blended it enough to get the lacto mixed well, and then this goes into the fermentation vessel. In classic Gentry style this is a plastic juice jug. Your fermentation vessel doesn’t need to be anything special as you can see from mine, haha. But it should keep the liquid as anaerobic as possible. For most people this means installing an airlock in the container. An airlock, used in wine and beer production, allows air out but not in, keeping the inside oxygen-free.

fish fertilizer - fermenting

Fish fermenting away in my homemade fermentation chamber

Whoa! What is that blue tube with the hose going into it?! It’s a homemade carbon filter I added to the system. It’s not 100% functional for what I want from it, but it does cut the smell completely. I know a number of people complained about the smell during fermentation. I’ll post another article on how to make your own carbon filter, then you don’t have to worry about the smell anymore. This also works well as an airlock.

If you’re curious about how fermentation is going, watch your airlock for bubbling. In my case my airlock is the carbon filter with the little outlet tube. So for me to see, I dip the end of the tube in some water. And what do you know – bubbling away! This indicates CO2 and other gases are being released through the process of fermentation, and is a great sign of a successful fish fertilizer production.

fish fertilizer - testing for fermentation

It’s easy to tell if your fermentation is going – just watch for air coming out. In an airlock watch for bubbles – in this system I dip the end of the tube in water to check for bubbling.

Now let’s skip to the end of fermentation to see the good stuff – final product! Fast forward 3 weeks. In the warm weather of the tropics here in the Philippines, this is more than enough time to complete fermentation. To bottle up my fish fertilizer, I’ll use a strainer and funnel, and pour it out of the jug right into the storage container.

fish fertilizer - straining the fertilizer

After fermentation is complete, I strain the liquid to avoid getting chunks in my fertilizer

Here’s the great thing, it’s SCENTLESS. Very nearly anyway, and the smell it does have is like wine, like a fruit wine or something, it’s wonderful. I mean wonderful compared to how it smelled going in. Fermentation really does some cool stuff. Who would have thought a rotten fish could have no smell.

Another cool thing, what’s left in the strainer! We started out with a nearly 1 lb fish. Scales, gills, bones, skull, everything went into the brew. It was blended initially and that helped dramatically to break up those big bones and increase surface area for microbes to work on. But there were still a lot of large bones at that stage. Now look at what’s left in the strainer after I’ve emptied the jug:

fish fertilizer - solid leftovers

There is very little solids leftover after fermentation – the fish was digested almost completely during fermentation

Amazing! Around 2 tbsp worth? Tiny! Out of that whole big fat tilapia, we end up with a little tiny pile of bones. And they are different. They aren’t brittle, they are soft and rubbery. They are clearly degraded, and will break down in the soil in no time. I added these directly to one of the planters.

And now you can see the fish fertilizer in it’s final jugs – more recycled plastic containers. I ended up with about 1.5L of fish fertilizer from that fermentation. This will be great for my plants, they need a bit of a nitrogen boost.

fish fertilizer - final product

The final product from this fermentation is 1.5L of fish fertilizer. I have it split into 1L and 500ml bottles.

Pretty cool stuff. It is really fun making your own fertilizer and seeing how fermentation produces such dramatic results.

I use this fish fertilizer in many applications:

2-4tbsp/gal in water for plants to green them up (normally just 2tbsp/gal but sometimes more)
1tbsp/gal applied to the compost pile, nitrogen boost and microbe feed
1-2tsp/gal in aerobic compost tea (very small amount as the oil tends to reduce aeration)
2-4tbsp/gal in anaerobic compost tea (or even more, there is no limit here)
0.5tbsp/gal in water to moisten animal feed bokashi prior to feeding worms/roaches/dog

There are all kinds of applications for this stuff as you can see in the list above. It is not only amazing as a direct fertilizer, but also as a microbe food source, nutrient source for large animals, and more. Get creative and play with it around your house. It is awesome stuff!

Keep on growing. 🙂

  • Can’t wait to try this. I need to wait a week for my lacto to be complete. It could be good also to wait for the carbon filter instructions so I don’t alienate my family!

    • Patrick

      Haha yeah, you know I never noticed a big smell during fermentation, but some people have complained about it. There is definitely a smell during fermentation, which dies when fermentation ends, it’s pretty neat. But anyway I’ll post the method on how to make the carbon filter soon, it’s simple and effective.

      Cheers,
      Patrick

  • David Di Cecca

    Is Whey powder an equivalent to Lacto serum? And if so how much powder would I use.

    • Patrick

      Hi David,

      Whey powder, as in the protein powder? No, that is a different thing. To make lacto, follow our recipe on making your own lacto serum.

      Cheers,
      Patrick

  • Marion

    I make milk Kefir which is fermented milk, could the Whey strained from this
    which has a wide variety of Lacto bacillus organisms be used as a substitute.

    • Patrick

      Definitely! Would be awesome!

  • Daniel

    Hi Patrick,

    I’ve been fermenting my fish for about a month now. Most of it has broken down but there still are some chunks and smell that resembles death but not nearly as bad as it was the first couple of weeks. There is separation of the oil and the liquid is almost an orange color. I noticed yours was more of a brown color. I just wanted to know if that sounds about right? We have cold weather at night and I don’t have the ability to blend the fish so I’m hoping that may be why its taking its time even though I did chop the fish into small pieces…

    • Patrick

      yep, that’s all fine. it will separate into layers if you let it sit, due to the oils. I need to add a picture of that.

      If you want to ferment more, just add more sugar and water. Help reduce the amount of chunks in your mix.

      Cheers,
      Patrick

  • HI Gil and Patrick,

    Any idea what the NPK values of this stuff might be? I’d like to go organic at our small hops farm and have unlimited access to fish. Hops need about 160lbs N/ ac. but not sure how you might gallons/ acre required at 2 tbsp/gal dilution. Thanks for the help and what a great site! Ryan

    • Patrick

      Hi Ryan – it really depends on what fish you use, how much water you add initially, etc. But they are low in inorganic Nitrogen. You would want to still use an organic fertilizer in conjunction with these, INITIALLY. Once you convert to organic and practice composting, green manure, cover cropping, etc, these will be excellent and adequate sources of Nitrogen. But it’s a process, and takes some time to match inorganic inputs. I don’t want to discourage you but as a commercial operation, I don’t want you to lose income.

      • HI Patrick,

        Thanks for the response. I’m not at all discouraged. I think this will be a great addition on our farm, once I get it figured out. I just finished mixing 500 gallons of this stuff yesterday. It’s smelt season up here and I’m brewing it in 55 gallon barrels. It’s a bit cold up here so hopefully, things will progress (albeit slowly). Everything else has gone organic but I haven’t been able to find a suitable (affordable) organic fertilizer. We’re already using composed cow manure and white clover for cover and would love to be done with the Jack’s 20-20-20 at some point. Our farm is on a trout stream so I need to be careful with the fertilizer inputs even if it means coming up a little short in lbs N/ ac.

        Thanks again,

        Ryan

        • Patrick

          Ryan,

          Sounds like you are taking environmental stewardship seriously, that is awesome to see. We need more people like you, and it’s one of the major themes of this site though I haven’t focused on it much since I’m busy enough covering the recipes and organic topics.

          Also looks like you’re well on your way to being full organic. The composted manure and cover crops should pay off after a few years – takes time to build up organic matter in the soil. Have you used biochar? Check out our page on biochar – I highly recommend it for increasing efficacy of inputs, organic and not. That also takes a few years to become fully effective, but the results in studies have been awesome.

          Cheers,
          Patrick

  • George

    Hi Gil and Patric!
    I am very excited with your website it is full of useful and practical information. I did the fish hydrolysate recipe but used live yoghurt whey instead of the suggested lacto-fermented serum. I let it ferment for 2 months (it’s still kind of cold here in Athens Greece, around 19 degrees Celcius, especially at nights) and finaly I got a mix of orange and gray colored liquid that smells “fish” and a little vinegar, not bad, not rotten, just “fishy”. Of course next time I will use the rice-wash serum that I already have brewing, but do you think this one is still good to use for my garden? I ask that because in your recipe you say it should almost have not any smell.
    Thanks,
    George

    • Patrick

      Hey George,

      Yep, that will be awesome for your garden, no worries. Yeah, depending on the fish used and such, there might be a little smell. But it should have a touch of alcohol or vinegar to the smell, like you observed, and it shouldn’t be foul or putrid. I think you’re on the right track and made a great batch.

      Cheers,
      Patrick

      • George

        Thank you Patrick for your response.
        To all people wandering if yoghurt whey can do the trick with fish hydrolysate, I have an answer!
        Yes, it worked for me. I used the amount stated in this recipe, but instead of rice-wash fermented lacto serum (which I had difficulties making it), I used fresh, homemade (greek) yoghurt whey. I made a couple of batches this way and I’m already using it regularly during watering on my vegetable garden and fruit trees with very positive results. I can’t wait to taste the first tomatoes or peppers of the season!
        The way to get whey is to get some un-strained yoghurt and simply strain it in a container using a sieve and a piece of cloth. Put it in the refrigerator and after about 5 hours it’s fully strained. Use the liquid as lacto serum substitude. It can also be used to ferment foods like vegetables, cereals, ketchup, etc. as a nutritional boost.
        Again, Thank you for this wonderful site!

        George

        • Patrick

          Excellent feedback George, I love your improvisation! That’s a great contribution to the recipe, I might have to add an addendum section for these recipes, alternative ways to make them.

          Cheers,
          Patrick

  • Taylor

    Patrick,
    Thank you so much for the information. I’m curious after fermentation is complete and you bottle your liquids is there any issue with expansion? Bluntly do your bottles explode or anything to that affect? I imagine if fermentation is completely done then no gasses would be emitted but I want to ask an expert .
    Thanks
    Taylor

    • Patrick

      Hey Taylor,

      Great question, YES – quite often fermentation goes a bit longer after you transfer to bottles, and in that case you need to make sure to crack the lid to let the buildup out each day, or keep in airlock. When fermentation is completely done, yes there isn’t expansion anymore, but that’s hard to see sometimes, so you will no doubt run into this issue at some point. Better to be aware of it. Because the bottles will explode, it’s happened to me more than once haha. Have fun! 🙂

      Cheers,
      Patrick

    • in most instances, it may “explode”. this is normally because the fermentation process may not be fully completed yet and still lots of undigested protein. what i do to accelerate the process is through aeration. put a bubbler like aquarium aerator and after a while, the “undigested” protein shall be “combusted” and eventually shall stabilize. no more “explosions”!

      • Guy

        HI Gil, Can you elaborate more on this aeration process?…how long would you leave the bubbler in? how long after initial fermentation would you do this?

  • Taylor

    Patrick,
    Ugh more questions have arose: does the mixture need to be stirred throughout the fermentation process, and where can I find your link on how to make your own carbon filter?
    Thanks,
    Taylor

    • Patrick

      Hey Taylor,

      No prob with the questions. You don’t need to stir during fermentation. I find that as long as you keep it anaerobic, stirring can help fermentation progress by mixing up all the ingredients again, but I wouldn’t remove the lid to stir or anything. Just keep the principles (anaerobic) in mind and you can do whatever within those bounds to help the process along.

      I haven’t posted the method for the carbon filter yet but I will later on – it’s pretty handy for keeping the process scentless. In any case, I don’t find the smell during fermentation to be overwhelming, it leaks out the airlock fairly slowly especially for small batches.

      Glad you’re having fun with the recipe, your plants will love it!

      Cheers,
      Patrick

  • Taylor

    Patrick,
    Thank you for the information. Iv seen people run their airlock exit through a bucket of water. If no air bubbles come out does this mean that the fermentation is done or can expect that the process might restart, and create more fumes? Is there anyway to be certain that the fermentation is complete or anyway to stop the fermentation . Refrigeration? I live in a cold climate where my access to fish is at the end of the growing season and I want to save my fertilizer till the spring without fear of explosion over the 6 months. Harsh right? Also I wonder would it be as advantageous to fertilize during fall, end of growing season, rather then before or during growth.
    Thanks again for your spring of knowledge,
    Taylor

    • Patrick

      Hey Taylor,

      Lots of questions there but I’ll try and answer them. Yes it can restart a bit after you transfer containers, so watch for that. You can refrigerate and that will SLOW fermentation but it wont stop it completely. Just crack the container every few days for the first while. Ideally you would just make the fish fertilizer, then leave it in airlock all winter. No need to transfer it, and the airlock will let air out as it needs to and keep it anarobic. You’ll want to fertilizer before and during growth. You can also fertilize during fall no prob, feed that nice winter cover crop to be turned in during spring.

      Cheers,
      Patrick

  • George

    Love this stuff, great informative article!

  • Taylor

    Hi again Patrick,
    Just getting to final steps of my LAB. Nervous haha, but all looks well. The three layers you speak of are they as follows: top thin film, middle (most of the quantity) foggy, and bottom thick curdy looking stuff?

    Do you dilute the final LAB before putting into the fish mixture? Or do you use pure?

    If you were going to ferment fish in a 55 gallon container/quantity how much lacto would you use? Would you keep the same ratio as with smaller batches?
    Thanks again,
    Taylor

    • Patrick

      Hi Taylor,

      Yeah that happens sometimes the curds sink, that’s ok. For your questions: Yes, dilute before adding to fish. For a 55 gallon drum of fish you would use the same rate as for smaller batches, although you could use less. I would just add a gallon of diluted serum. I just picked that number, it should be plenty, although at the rate recommended in the recipe it would be 6 L i think. Up to you how much you add.

      cheers,
      patrick

  • Hi, I am new to all of this and would like to make my own fish fertilizer. I had a question, can I use frozen fish? Tried catching fish but it didnt work out. Fish is fairly expensive here in Japan. How long will this keep in a fridge, can I freeze the end product?
    TX, enjoy your articles
    Hugo

    • Patrick

      Hi Hugo,

      Yep you can use frozen fish no prob – thaw it first obviously..

      Once fermented it will keep a long time.. Don’t freeze it though or you’ll kill the beneficial microbes in it.

      Sorry for the late reply, hope you were able to make some!

      Cheers
      Patrick

      • Hi, TX for the reply. I was in the local supermarket and it was close to closing time. They had these small fish (ayu) on sale for 1$ and it. Was just the amount I needed. I did make the stuf, it’s been 2 months since I started it. I haven’t dared to take the airlock off, ha, curious if it worked. I did follow your sample recipe.
        I did have another question, I started composting, 1 part greens and 3 parts brown. Lots of brown bamboo leaves where I live. I used a rectangler bin and drilled some holes in the bottom and back side. Here’s my ?, I have a drip pan to catch the liquid that comes out, can I used that for fertilizing my veggies? Implored it in a bin and deluded it with water and then used it like that. Is that correct, should I do some thing else with it?
        TX for taking of your valuable time. To answer,
        Hugo

        • Patrick

          Hey Hugo,

          You can definitely use the drippings, and diluting is a good idea. Your plants will love it! You can probably also check the fish fertilizer, it should be finished now. Shouldn’t smell too strongly, and shouldn’t smell much like fish anymore either. Let me know when you’ve checked it out.

          Cheers!
          Patrick

  • Ed

    Dear Patrick,

    I have thoroughly enjoyed learning these things from you, LAB and fish fertilizer making, including from those great answers that you have given to relevant questions in your forum. Thank you very much. I am just starting a small organic vegetable farm. Before I start fermenting some fish for fertilizer, I want to make sure that my project wont pollute the air of my neighborhood by fabricating a similar filter system with airlock as yours to mitigate the smell of decomposing fish. I therefore hope that you can give me some leads as to where to buy this airlock. I am writing you from Cebu City.

    • Patrick

      Hi Ed,

      You can make the air filter airlock no problem. Just get some carbonized rice hulls, which you can get here in Philippines pretty easily. Add those to a length of pvc pipe, cap both ends and connect to your fermentation vessel via clear plastic tubes as shown in my pic.

      I will be issuing a post with detailed instructions also.

      Sorry for the late reply, I’m glad you’re enjoying the site though, keep reading!

      Cheers,
      Patrick

  • Angelo

    Hi there, I am familiar with the lacto serum and have made many batches with great success, I work in a restaurant in Canada and have saved a fair amount of salmon scraps as we process/clean alot if this for our guests, I tried to make a batch of the fish hydrolysate for a few friends and let it sit for just over a month as per your directions, however the entire thing ended up smelling l like strong cheese, I have since been afraid to try t to use idid I go wrong somewhere?

    • Patrick

      Hey Angelo,

      Sorry for the late reply, I’ve been swamped…It should be fine. As long as it doesn’t smell putrid, you should be ok. You might try adding less lacto next time, but in any case this batch sounds fine to me.

      Cheers,
      Patrick

  • Angelo

    Any help you could offer would be amazing, I have played with fish emulsion before with HUGE success, but as I said in my previous post, the cheese smell has me concerned

  • Dan

    Hey Patrick,

    Greetings from Niagara Falls Canada, thanks for all the great info, I’ve made the bloom, grow, lacto and BIM. Seen major improvements in my garden this year…so much so I’m expanding and tripling my garden space.

    I also attempted the fish fert. However the fish fert is smelly, fishy and kinda gross. I strained it, got only small bone fragments like you displayed above. I followed the steps to the letter. It’s the same color, has oil separation. I’m wondering if the cool weather we’ve has this last month would have called for a longer fermentation? Would adding a bit of water and more sugar help complete the fermentation and reduce the smell? Or can it be used as is? Not sure if I should use it, I’m testing it on a small section to see if any adverse effects. I’d would love your input on how you’d proceed in this situation?

    thanks again for all your time!!

    • Patrick

      Hi Dan,

      Sounds like it could have used some more fermentation and cooler weather would be the culprit. You are exactly right, you can add a bit more water and a bunch of sugar, seal it up and it will ferment again. Try to keep it warm, like 25 and above, if you can.

      Note, you should be able to use it as is no problem, your plants should love it. I would use it as a soil drench obviously haha, but yeah should be fine. Make sure you dilute it appropriately, maybe start with 1 tbsp/gal just to be safe. Let me know how your test goes anyway.

      If it were me I’d probably start using it now but also add some more sugar and water and keep it sealed as much as possible so it keeps fermenting. I’d also try to keep it somewhere warm to make sure it really ferments, but that’s kinda optional, if its a big hassle I wouldn’t worry too much about it..

      Cheers,
      Patrick

  • […] I think this batch will get to the same place as fish fertilizer in terms of smell. Remember when making fish fertilizer, during fermentation you get all kinds of smells out of the bottle, as the fish is digested. […]

  • Juan Pablo

    Hey guys I made a batch of this recently in a 1000L IBC. We got all our fish waste from a local seafood processing factory. Mainly Squid guts and prawn heads/shells.
    We’ve been bottling it up this week and have found that sometimes its a dark liquid and other times its pale/watery, we’ve tried mixing it with a long pole but the results are varying. Have you had this problem?
    How much water and how much lacto serum would you recommend to put in 1000L. We filled it to about 2/3rds full of fish guts and the rest water with a 15L bucket worth of serum. Still took over three months to be completely finished. We had to add water a few times because it seemed the top just kept drying out and not breaking down. It was bubbling the whole time though, so the bacteria was still alive.

    Also it definitely does not smell sweet. We had a bit leak out of the lid in the car last week and we’re still trying to get the smell out! I don’t mind it so much and can bottle it up easily but everyone else runs out of the shed screaming! 🙂

    • Patrick

      Wow that’s awesome!! Hmm yeah I would have used more water, like 2 parts water for every part fish guts. But doesn’t matter! Just affects how easy it is to work with, as you’ve noticed. The fats and oils will rise to the top, and if you haven’t blended the stuff going into it, the chunks will float because they contain fats and oils..

      Yeah if you want to make it scentless you’ll have to ferment again with more sugar and lacto, I think it has more to go if it has the smell. That said there is no need to, you can use it as is and it’s gonna be an awesome fertilizer!

      Cheers
      Patrick

  • Rollray Galguerra

    vcan yakult be used in place of lacto basillus?

    • Patrick

      Hi Rollray,

      Yep it can be used instead in a pinch, though better to make your own lacto if you have the time.

      Cheers
      Patrick

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