Fish meal is a staple in most organic gardens across the world. It's a byproduct of the fish industry, and a great use of what would other wise be a waste product. Obviously the fish industry wanted to find a way to profit off of their waste, and organic gardeners were there to make that happen. It's honestly a great symbiotic relationship, and a wonderful re-purposing of an other wise not very useful ingredient.
In America most of us grew up learning of the Native Americans placing a fish in the hole of each corn plant. I sure don't remember learning about why this was so beneficial, but as I got into gardening more I learned the native Americans had it figured out. Obviously there were no soil tests, ph testing, micronutrient tests, etc.., but for the limited knowledge they had of how soil worked, that single fish was ground breaking. Yes that was a pun.
One of the benefits the Native Americans had no way of testing, was that fish can be used as a microbial food in the soil. In present day agriculture, fish meal can help to stimulate microbial populations. As most know, the more active, and diverse the microbial population the healthier the over all soil can be. Increased microbial populations can lead to higher rates of nutrient cycling, disease suppression, and many other plant health boosting benefits.
Fish meal Contains Nitrogen
Fish meal often contains high amounts of nitrogen. Because of it's make up, the nitrogen will be a slower release that can last most of the season. So one single application of fish meal could last you until harvest in your tomatoes, and other vegetables. In cannabis production, especially indoors, a single application may last you multiple harvests. Since the nitrogen in fish meal is a slower release, if you are in need of a quick shot of nitrogen, try something like an alfalfa tea.
Fish Meal also Contains Phosphorous
Fish meal will be the entirety of the fish parts ground up. Where as fish bone meal is just the bones. Since fish meal is the entirety of the flesh, bone etc.. it also contains phosphorous. This phosphorous will be a slow release phosphorus source that can be season long just like the nitrogen. That being said, if you have access to both fish meal and fish bone meal, they do work well together. Just make sure not to over apply either and inadvertently add to much phosphorous to the soil.
Fish Meal Use Rates:
Fish Meal Use Rate For Potting Soils
1-2 tablespoons per gallon of soil
Fish Meal Use Rate Per Yard Of Soil
2lb- 5lb. Per cubic yard of soil
Fish Meal Use Rate For Gardens
2.5lb.- 5lb. Per 100' square foot of soil
When adding fish meal to potting soils its always a best practice to mix it in before you pot. That being said, if you have existing potting soil that you are wanting to fertilize then there are multiple different ways to add it to your soil.
If you are growing cannabis in a no-till living soil style pot, or soil bed then top dressing it can be sufficient because the worms, microbes, micro-arthopods, etc.. will digest your fish meal and make it bio-available to the plant. If you are in a standard potting soil situation with no worms, etc.. then lightly scratching the fish meal into the surface is a fast and easy way to add it to your pots.
When scratching an amendment in it really just means what it says. You will sprinkle the fish meal around on the soil surface, and with either your hand, or a tool, scratch in the fish meal to the top few inches of your soil. This will get the nutrients down where the microbes are and begin the digesting process of making the nutrients bio-available in the rhizosphere.
Alternatively in smaller house plants, and pots with limited ability to scratch in an amendment, you can mix the fish meal into water, and water in the fish meal. Some of it will penetrate the surface, and get below where the microbes can do their thing.
How I use fish Meal in My Gardens
I personally use fish meal in my vegetable gardens, and obviously in the soil we manufacture. I also will use it in my cannabis pots and beds, as an amendment that we top dress.
When adding it to my vegetable gardens, I like to add my amendments early in the season to give them a few months to digest, and become available. Depending on whether I am doing no-till vegetable beds, or containers, I will either top dress, or scratch it in. I typically only add it one time per season. Obviously this is for personal use, and if you have any kind of money on the line it is always best to get a soil test.
In our cannabis pots and beds we use it as a top dress as the worms will do the heavy lifting when it comes to digesting it. I typically will only use it once per cycle. In cannabis production, since it's such a high value crop, getting your soil tested, as well as doing tissue testing is always a good idea.
Fish meal is always a go to amendment that I suggest to most home vegetable gardeners. Whether trying to grow in native soil, or even a store bought potting soil, as long as you apply a reasonable amount, you should see positive benefits in most gardens.
With a proven track record of thousands of years, fish products work very well in most soil situations. What better way to turn trash into treasure then using fish meal in your garden.