How To Make Fish Fertilizer

If you’re looking for a powerful, natural boost for your garden, learning how to make fish fertilizer is a fantastic skill. This simple and effective homemade solution feeds your plants and enriches your soil with minimal cost.

Commercial fish emulsions are great, but they can be pricey. Making your own puts you in control of the ingredients and saves money. It’s a great way to use scraps you might otherwise throw away, like fish parts from cleaning your catch or leftovers from dinner.

This guide will walk you through the easy process. You’ll learn why it works so well and how to use it safely in your garden.

The core process for making fish fertilizer is straightforward: you break down fish parts in water. This creates a nutrient-rich “tea” you can dilute and apply to your plants. The main methods are fermentation and blending, with fermentation being the most common.

Why Use Fish Fertilizer in Your Garden?

Fish fertilizer is packed with benefits. It provides a balanced, slow-release source of major nutrients.

Nitrogen (N): Promotes lush, green leafy growth.
Phosphorus (P): Supports strong root development and flower/fruit production.
Potassium (K): Aids in overall plant health and disease resistance.

It also contains valuable micronutrients like calcium and magnesium. Beyond feeding plants, it adds beneficial microbes to your soil. These microbes help break down organic matter, improving soil structure and fertility over time.

What You’ll Need: Materials & Ingredients

Gathering your supplies is simple. You probably have most of these items already.

Fish Parts: Any non-oily scraps work—heads, guts, bones, skins. Avoid using fish cooked with oils, salts, or heavy spices.
A 5-Gallon Bucket with Lid: A food-grade plastic bucket is perfect. The lid is crucial for containing the smell.
Water: Non-chlorinated water is best. Use rainwater, pond water, or let tap water sit out for 24 hours so the chlorine evaporates.
A Sugar Source (for fermentation): Unsulfured molasses or plain brown sugar. This feeds the beneficial bacteria.
Stirring Tool: A long stick or old wooden spoon.
Strainer & Cheesecloth: For filtering the final liquid.
Storage Containers: Old milk jugs or juice bottles with tight-fitting lids.
Optional: A handful of garden soil to inoculate with microbes, or some finished compost.

Step-by-Step: The Fermentation Method

This is the classic, low-effort method. It uses beneficial bacteria to break down the fish.

Step 1: Prepare Your Bucket

Place your fish parts in the 5-gallon bucket. Fill the bucket about 1/3 to 1/2 full with the scraps. Don’t pack it too tightly; the water needs to circulate.

Step 2: Add Water and Sugar

Cover the fish completely with your non-chlorinated water. Leave about 4-6 inches of space at the top. Then, add about 1 cup of molasses or brown sugar. This step is key for encouraging the right kind of bacterial growth.

Step 3: Stir and Cover

Give the mixture a good stir to dissolve the sugar. Place the lid on the bucket, but do not seal it airtight. Gases will build up during fermentation. You can snap the lid on loosely or drill a small hole in it and plug it with a bit of cotton.

Step 4: The Waiting Game

Store the bucket in a warm, out-of-the-way spot. Every 2-3 days, stir the mixture gently. This releases gases and prevents it from becoming anaerobic. You’ll notice bubbles and a strong odor—this is normal. The fermentation process typically takes 2 to 4 weeks.

The mixture is ready when most of the solid matter has broken down and the bubbling has mostly stopped. The smell will have mellowed from a sharp rot to a more earthy, yeasty aroma.

Step 5: Strain and Store

Line a strainer with cheesecloth and pour the liquid through it into another container. Squeeze or press the solids to extract all the liquid. Compost the leftover sludge. Pour the strained fish fertilizer into your storage bottles, label them, and store them in a cool, dark place. It will keep for several months.

Alternative: The Quick Blend Method

If you need fertilizer faster and have a strong blender you don’t mind dedicating to the task, you can make a quick version.

Combine 1 part fresh fish scraps with 2 parts water in a blender.
Blend on high until you have a smooth, milky liquid.
Strain this mixture through cheesecloth into a bucket.
Add another 2 parts water to the strained liquid.
This blend must be used immediately or within a few days, as it will spoil quickly. Do not store it for long periods.

How to Use Your Homemade Fish Fertilizer

This is a concentrated fertilizer and must be diluted. Using it full-strength can harm plant roots.

General Dilution: Mix about 1 tablespoon of fertilizer per gallon of water. For very young seedlings, use half that strength.
Application: Apply it as a soil drench around the base of your plants every 3-4 weeks during the growing season. Avoid spraying directly on leaves in full sun, as it can cause burning.
Best Time to Apply: Early morning or late afternoon is ideal. Water the plants lightly with plain water first if the soil is very dry.

Always do a small test on a few leaves or one plant first. Wait 48 hours to check for any adverse reaction before treating your whole garden.

Managing the Odor

The smell is the biggest challenge. Here are some tips to minimize it:

Add a handful of finished compost or garden soil to the fermentation bucket. The established microbes can help reduce odors.
You can also add a few tablespoons of crushed rock dust or biochar.
Keep the bucket lid securely on and its location well-ventilated but away from living spaces.
When applying, incorporate the diluted fertilizer into the soil immediately rather than letting it sit on the surface.

The odor dissipates quickly after application, usually within a few hours. Your plants certainly won’t mind it.

Common Mistakes to Avoid

Even simple processes can have pitfalls. Here’s what to watch out for.

Using Chlorinated Water: Chlorine can kill the beneficial bacteria needed for proper fermentation.
Sealing the Bucket Tightly: This can lead to a dangerous pressure build-up and possible explosion.
Not Diluting Enough: Always err on the side of a weaker solution. You can always add more, but you can’t fix burned roots.
Applying to Dry Soil: Always ensure the soil is moist before adding liquid fertilizer to prevent root shock.
Using Oily Fish or Cooked Scraps: Oils can create a rancid layer and attract pests. Salt from cooked fish can harm soil biology.

FAQ: Your Questions Answered

Can I use any type of fish?

Yes, but freshwater or lean ocean fish are best. Avoid very oily fish like mackerel, as the excess oil can complicate the process and smell worse. Shellfish scraps can also be used.

How long does homemade fish fertilizer last?

Properly fermented and stored in a sealed container in a cool place, it can last 6-12 months. The quick blend method should be used within a week.

Is it safe for all plants?

It is excellent for most vegetables, flowers, and fruiting plants. Use a more diluted solution for young seedlings and be cautious with plants that prefer poor soil, like some native herbs.

Will it attract animals to my garden?

The strong smell during fermentation can attract critters, so secure your bucket. Once diluted and applied to the soil, the risk is minimal, especially if you water it in well. Burying any leftover solids deep in your compost pile is a good idea.

What’s the difference between fish fertilizer and fish emulsion?

Fish emulsion is a specific type of fish fertilizer that has been processed and sometimes deodorized. Your homemade version is a broader “fish fertilizer” that acts similarly but retains more of its raw microbial life.

Making your own fertilizer is a rewarding way to close the loop in your garden. It turns waste into a valuable resource, giving your plants a natural feast. With a little patience and these simple steps, you’ll have a powerful, cost-effective plant food ready for the season. Just remember the golden rules: ferment with molasses, dilute well, and your garden will thrive.