How to Make a Fungicide Using Copper Sulfate Crystals

Written by Naomi Meza


Posted on July 08 2022

Are you concerned about the chemicals in conventional fungicides and want to take a more natural approach to protect your plants?

You can make your fungicide using copper sulfate crystals, calcium hydroxide, and water.

This mixture is called the Bordeaux mixture and has been used for years to control fungal diseases on vegetables, fruits, ornamentals, and turf.


Related Post: A Guide to Natural Herbicides, Pesticides and Fungicides for Your Garden


It is a safe and effective way to treat diseases such as black spots, powdery mildew, and rust.

Copper ions in the Bordeaux mixture are deadly to fungi but have no effect on plants.

Bordeaux mixture suffocates the fungus and prevents it from growing and reproducing.

It is most effective when applied before the disease appears but is still effective when applied to early signs of disease.

Before going through the step-by-step process of how to make a copper fungicide, let's look at what a fungicide is and how it can benefit your plants.

What is a Fungicide?

Person applying fungicide on plants

A fungicide is a pesticide used to prevent, destroy, or control fungal infections on plants by killing fungi or inhibiting their growth and reproduction.

Fungi do not have chlorophyll and cannot make their food, so they depend on plants for food.

As they feed off the plant, they weaken it and make it more susceptible to disease and pests. Some fungi also produce toxins that can kill plants.

Fungicides control various plant diseases, such as mildews, rusts, blights, and leaf spots. They also prevent the spread of disease from one plant to another.


Related Post: The Difference Between Fungi and Bacterial Infections in Your Plants


How To Make a Bordeaux Mixture

Woman applying fungicide from a bottle onto her tree

The effectiveness of the Bordeaux mixture depends on following the right procedure and using the right proportions of ingredients.

The ratio of copper sulfate to hydrated lime (calcium hydroxide) to water is 10:10:100. You will need 10 pounds of copper sulfate and 10 pounds of calcium hydroxide for every 100 gallons of water, as a general ratio typically used in larger scale applications of the Bordeaux mixture.


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If you need to apply on a smaller scale though, you can do so using the instructions below to make what's called a "stock solution."

Please note that copper sulfate and calcium hydroxide require safety precautions when handling them.

Wear gloves and a dust mask to avoid contact with skin and breathing in the powders.

1. Begin by Dissolving the Calcium Hydroxide

Calcium hydroxide

Fill a bucket with 1 gallon of water and 1 pound of hydrated lime. Let this mixture stand for two hours.

2. Dissolve Copper Sulfate in Water

Package of blue copper sulfate crystals

Add 1 pound of copper sulfate to a gallon of warm water and stir until it is completely dissolved. 

3. Combine the Two Mixtures

Hand holding a blue bucket

You can now combine the two solutions to make a 2.5 gallon Bordeaux mixture. Measure two gallons of water in a durable bucket.

Vigorously shake the copper solution from step 2 above, and add 1 quart of the copper solution to the bucket with two gallons of water. (You'll want to make sure you add the copper before the lime, every time.)

Next, shake the lime mixture from step 1 and add 1 quart of this solution to the same two gallon bucket.

If adding to a sprayer, stir and shake the Bordeaux mixture several minutes before transferring from the bucket to the sprayer. 

4. Apply the Bordeaux Mixture to Your Plants

Fungicide applied to plant leaves

The Bordeaux mixture is now ready to use. Use a garden sprayer to apply the mixture to your plants, and coat all the leaves thoroughly.

This homemade Bordeaux Mixture should be used the same day you prepare it for the best results.

Protect Your Vegetables From Disease With Bordeaux Mixture

Tomato plants in the garden

Making your own Bordeaux mixture is a safe and effective way to control fungal diseases on vegetables.

Apply the mixture before the disease appears for the best results. Copper sulfate crystals are a key ingredient in the Bordeaux mixture, which has been used for years to control fungal diseases.

We sell copper sulfate crystals of the highest quality and purity!

We take pride in providing our customers with the best products and services possible to support a healthy and beautiful garden.

Buy our copper sulfate crystals today to make your own Bordeaux mixture!



  • Comment author

    @Kurt: Thank you for your response. As previously mentioned, the ratios have been updated. Unfortunately, we cannot account for every ratio needed so if you require any amount smaller than what has been provided, you’re welcome to research further. Thanks again!

    Posted by Greenway Biotech | February 15, 2024
  • Comment author

    Agree with the previous comments, the ratios sound simple but are incorrectly measured in your directions, 1:1:10 is meaningless for any units smaller than 10 gallons as pounds and gallons do not relate in the way liters and grams can. The ratio of (dry) ounces of chemical to (liquid) ounces of water, for instance is 1:1:80 (1280/16=80)

    Posted by Kurt | February 15, 2024
  • Comment author

    Hello, thank you for your concern. The ratios have been updated.

    Posted by Greenway Biotech | August 18, 2023
  • Comment author

    Wow! I can’t believe you still haven’t fixed the mistake in the article as also noticed by the previous commenter. Mixing a pound of both Copper Sulfate and Calcium hydroxide, to a gallon of water will poison everything it touches. Surly it would be a tenth of a pound to a gallon.

    Posted by John | August 18, 2023
  • Comment author

    The formula ratio you recommended of the Bordeaux mixture is 10 lb : 10 lb : 100 Gallon respectively for Copper sulfate, Calcium hydroxide and Water, namely 1 lb : 1 lb : 10 Gallon or 454 g : 454 g : 38 Litter. However, in your example of making small scale of this mixture, you used 454 g for each of Copper sulfate and Calcium hydroxide, but the total amount of the water is only 9 litters (3.5 L + 3.5 L + 2 L) instead of 38 Litter. Please explain it or make a correction.

    Posted by Tommy | October 13, 2022
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