Along with seaweed, fish has been used as a fertilizer for centuries.
But using fish as fertilizer does beat liquid seaweed in one way – the major nutrients it contains, especially nitrogen (N) and phosphorus (P).
N and P are two important elements that are often deficient when our gardens aren’t yet up to a point of cycling nutrients optimally (which is most of the time).
Here’s why we need them:
- Nitrogen. Is the building block of proteins in plants, and so ultimately proteins in our body. We don’t need all that much nitrogen in the garden, but we do need a quality source, and that’s where liquid fish fertilizer comes in.
- Phosphorus. This element is important not just for root growth (as is the common myth), but it’s central to photosynthesis and building carbohydrates, and it’s involved with transporting almost every other mineral throughout the plant. Without phosphorus, our plants just aren’t going to be very healthy.
Seaweed has nutrients, too, but we especially use it for the natural plant growth regulators, whereas with fish fertilizer, it’s more about the nutrients.
Plus, if you get a quality fish product, you’ll be getting oils and proteins that feed microbes – that’s why I think of it as true whole food nutrition.
As with seaweed, I generally prefer a liquid fish fertilizer as being the most economical when compared to a fish meal.
How To Make Fish Fertilizer
This is some smelly good fun!
Get some fish (ocean fish is much preferred, but any fish will bring in at least some benefits) and grind it up in a blender or food processor. You’ll need a solid machine to break through the bones.
Add water to cover the mixture and then process some more until it’s all blended up nicely.
There you go – you have a basic liquid fish fertilizer.
Now, you could use it right away by mixing it with 10 parts water and watering plants.
But to get much more benefit, you should ferment it further so the nutrients will be more available for plants.
For that, I use 1 teaspoon of SCD/EM per cup of fish/water mixture, but if you don’t have that around and you’re a real do-it-yourselfer, other kinds of probiotics will offer at least some help.
Yogurt or kefir or some other lactic acid culture are good choices – use the same ratio as for the EM above. Or if you have a probiotic supplement, that will offer something too.
Then add 1 teaspoon of sugar or dextrose per cup of fish/water to give the microbes an energy source.
Put the whole mixture into a container with a lid or towel over the top, but don’t tighten the lid because there will be gases produced that would cause the container to explode. So just leave the lid slightly off, or use a carboy that allows gases to escape without oxygen getting in.
After a month or two, the horrible smell will be gone, which means the fish has been consumed by the microbes and your fish fertilizer is extra special and ready to go.
It will be much more beneficial than the fresh fish fertilizer at this point because the microbes have made the nutrients more available to the plants.
Finding A Quality Liquid Fish Fertilizer
By quality, I generally mean a fish hydrolysate fertilizer instead of a fish emulsion fertilizer:
- A liquid fish emulsion has had most of the fats and proteins removed for use in other products (like fish oil supplements and pet food) and also denatured because of the high-temperature cooking process used. That high temperature destroys a lot of the beneficial components of the fish. Also, chlorinated city water is generally used, so the end product is often very high in chlorine – not good for plants and microbes. An example is the (unfortunately popular) ‘Alaska Fish Fertilizer’ made by chemical company Lilly Miller.
- A hydrolyzed fish fertilizer is going to retain all that good stuff because it’s done at cooler temperatures, using enzymes, so it retains its vitamins, amino acids and enzymes. A good hydrolysate will have this done before all of the bones, oils, etc. have been removed, when the fish are still fresh – that also means it doesn’t smell bad, or at least not as bad as an emulsion that uses rotting fish.
Note that some companies will create a liquid fish emulsion fertilizer and then add enzymes back in after so they can call the product ‘hydrolyzed,’ but still, many of the beneficial components of the fish will have been destroyed or denatured during the processing.
Now, you won’t see anyone else who sells a hydrolysate saying this, but I actually don’t want to imply that a fish emulsion is useless – it generally has a higher nitrogen number and can be beneficial for soil applications.
But a fish hydrolysate is more of a whole food and is definitely better for encouraging beneficial microbes and for foliar feeding.
I should also mention fish meal fertilizer. It’s a great soil additive, but it’s really expensive, especially when shipping is factored in. Any kind of liquid fish fertilizer is going to be much more cost-effective than a fish meal fertilizer.
The Hydrolyzed Fish Fertilizer I Use
I’ve experimented with several of the best liquid fish hydrolysates on the market and I’ve been happy with most of them.
I settled on the organic fish fertilizer I use now called Neptune’s Harvest because even though it’s a little more expensive, it’s much more nutrient-dense so the application rate is much lower, making it a better deal in the end.
Plus they do a great job of properly processing the fish to retain all the beneficial components. The fish come from the deep, cold waters of the North Atlantic ocean, not near the polluted shore.
There are freshwater fish liquid fertilizers available, but that misses the point because it’s ocean fish that are full of micronutrients, due to the fact that they live in the nutrient-dense ocean.
With this product, once the fillets are removed for human consumption, the rest is made into the fish fertilizer.
It used to be dumped back out in the ocean and was actually creating a dead zone, but they’ve found a way to make good use of it.
I’m very concerned about the overfishing of the oceans, but the way they’re taking this byproduct of fishing that was causing environmental problems solves a lot of the problem for me.
But it certainly could be argued that it’s creating yet another reason to continue fishing the oceans, which is a valid point. The reason I haven’t stopped using it is that it’s just so beneficial for the garden, and if a little bit of ocean fish helps my organic garden produce more food – and much more nutritious food – I think it makes a lot of sense.
As with almost all organic liquid fish fertilizers, they’re using a touch of acid to drop the pH because otherwise, the microbes in the product would get so active that the container might explode.
In this case, it’s phosphoric acid, the same stuff they use in soda like Coca-Cola that is really not good for us to be consuming, but in the garden, it is VERY useful.
This little amount is allowed in organics (indeed this product is OMRI-Listed), and I would strongly prefer to have it in there than not.
How To Use Fish Fertilizer
Shake well before each use because sometimes there’s a thick part that separates out.
Once you’ve mixed with water, use it the same day.
Here are their suggested application rates:
- House Plants: Use 1 tablespoon per gallon of water every 1-2 weeks.
- Outdoors: Use 2 Tbsp per gallon of water every 1-2 weeks.
- Lawns: Use 1 gallon for 8000 sq ft every month.
- Seeds: Use 1 teaspoon per cup of water for soaking seeds.
They suggest applying until the soil is saturated or as a foliar feed until the leaves are wet.
That may be enough for you but it doesn’t really tell you how much to apply overall, so I’ve also dug into their agriculture recommendations to see if I could find a little more detail.
They recommend 3 gallons of product per acre, 4 times per year. That works out to about 1 quart per 1000 square feet per year, so that’s what I aim for.
For example, you could use 1/2 cup of liquid fish fertilizer per 1000 square feet every month for 8 months of the year.
Note: Since I also use sea minerals fertilizer, I alternate them every other month (eg. fish in March, sea minerals in April, fish in May, etc.). I use seaweed every month along with them.
I suggest mixing it with at least 50 times as much water, which would be 1.5 gallons for 1/2 cup of fish. Or just set a hose-end sprayer to spray 5 Tbsp per gallon. If the sprayer has trouble sucking it up, you can instead mix it with equal parts water in the sprayer and then setting the sprayer to 10 Tbsp per gallon.
You Can Get It Here
In summary, this liquid fish fertilizer:
- Provides many benefits, but is especially known for providing nitrogen and phosphorus that promote rapid plant growth, as well as the complete fats and proteins that microorganisms need.
- Is a hydrolysate, processed with enzymes at cool temperatures in order to retain all of the beneficial components.
- Is organic, OMRI-Listed, and not even too smelly.
Just choose your container size and click ‘Add To Cart’ up above!
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