Maybe you’ve heard of hydrogen peroxide being recommended for hydroponics, and you’re baffled. Why would you use a sanitizer in a system with living plants? Won’t it hurt them?

Not at all!

Hydrogen peroxide (H202) in a hydroponic system results in better germination of seeds, increased oxygenation and purity of water, and more growth overall.

In this article, we’ll go over why you should use hydrogen peroxide in your hydroponic system and how to do it successfully.

What is Hydrogen Peroxide?

Hydrogen peroxide is essentially water with one more weakly attached oxygen molecule–instead of H2O, you get H2O2.

It belongs to a chemical group known as peroxides, which are characterized by their oxygen-to-oxygen bonds. These chemicals occur naturally in small amounts in nature, including in the human body.

Hydrogen peroxide is the weakest member of this group, meaning that its oxygen bond decomposes more easily than that of other peroxides.

All of hydrogen peroxide’s hydroponic growing uses come from its instability as a bonded structure. When an H2O2 molecule comes into contact with water, it separates into a water molecule and one pure oxygen molecule.

The single oxygen molecule then does one of two things:

1. It comes in contact with another oxygen molecule and forms O2, increasing the overall oxygen content of the water solution.
2. It comes in contact with an organism, such as an algae spore, bacterium, or microbe, and destroys it through oxidation. 

H202 is common throughout the natural world, including:

• Rain
• Snow
• Atmospheric clouds
• The human body

The French chemist Louis-Jacques Thenard first discovered hydrogen peroxide in 1818. At the time, he dubbed it “oxygenated water.”

It was, however, difficult to produce in mass quantities thanks to the unstable nature of the oxygen bonds. The modern manufacturing process was patented by the German chemical company BASP in 1939.

Since then, hydrogen peroxide has become an ingredient in hair dye, bleaching solutions, first-aid disinfectants, and, most recently, hydroponics. 

Why is Hydrogen Peroxide Good for Hydroponics?

Glad you asked! This humble chemical provides a number of huge benefits for a hydroponic system:

1. Neutralizes chlorine
2. Increases the amount of nutrients your plants can absorb
3. Perfect for cleaning and sanitizing your system
4. Speeds up seed germination

Let’s look at each point in detail:

1. Chlorine Mitigator

In the U.S., municipal water systems treat tap water with chlorine to eliminate certain harmful bacteria.

Per government standards, the chlorine levels are deemed safe for human consumption. However, in the closed loop of a hydroponic system, chlorine is a contaminant that can weaken or kill your plants.

Thankfully, H2O2 in hydroponics is a very effective dechlorinator. It also helps reduce or eliminate the presence of pesticides or sulfates, as well as eliminate pathogens, bacteria, and algae. 

This ability of hydrogen peroxide to purify water is especially valuable in systems that run with water over 72 degrees F. Warm water is much more susceptible to algae or bacterial growth than cold water, so sanitation becomes an extra-important step. 

H2O2 simplifies this process because it can be added to the water of an already-full reservoir and eliminate any of these harmful organisms, without causing harm to the roots of the plant.

2. Increase Water Oxygen Content and Nutrient Uptake

Oxygen is a critical factor in how well your plants absorb nutrients. Even if your hydroponic solution has the perfect balance of every nutrient, your plants can’t access them if oxygen levels are too low. 

Hydrogen peroxide easily decomposes, releasing its two oxygen molecules into the reservoir water, thus increasing its oxygen content.

Thanks to the oxygen that H2O2 adds to the water in the root zone of your hydroponic crop, a dose of hydrogen peroxide in your reservoir can boost nutrient uptake to the roots of your plant.

This creates more vigorous plant growth, as well as a healthier root system overall, leading to a more productive and long-lived plant.

3. Sanitizes with No Residue

Hydrogen peroxide is one of the best disinfectants you can use on your hydro equipment due to its mode of action. 

It effectively kills bacteria and microbes when in its H2O2 form, but then readily dissolves into harmless oxygen and hydrogen once in contact with water.

This differentiates hydrogen peroxide from sanitizers like bleach, soap, or vinegar, which all tend to leave traces of themselves behind, no matter how much you rinse your equipment.

You can even use hydrogen peroxide to kill algae in hydroponics without removing your plants from the system, as well as Pythium, Fusarium, and mold.

The H2O2 only oxidizes bad bacteria and leaves the roots totally unharmed.

4. Faster Seed Germination

Exposing seeds to a brief dose of hydrogen peroxide will speed up their germination. 

This is probably thanks to a combination of the H2O2 doing a few things:

• Killing off any harmful bacteria
• Gently corroding the chemical on the seed’s casing
• The introduction of more oxygen into the water of the germination chamber

To use hydrogen peroxide to increase germination, place 1 teaspoon of diluted H202 in 1 cup of water. (We’ll talk about the details of diluting H202 just a little alter on.)

Then use a sieve or mesh bag to dip and immerse your seeds in this solution for one to two minutes.

Sow as usual, in soil or in soilless planting medium, and watch the little plant babies pop up in record time!

Where to Buy Hydrogen Peroxide

The hydrogen peroxide that you can buy in a drug store comes in concentrations of 3% – 8%. This hydrogen peroxide has been pre-diluted, and since it has to have a long shelf life, it also contains synthetic stabilizing compounds that may not be great additions to your closed-loop hydro system. 

So for hydroponics, the higher-proof, higher-purity food-grade H2O2 is much more effective. A concentration of 33% – 35% is ideal.

That sounds like quite a high proof, but remember that you’ll be diluting a small amount in several gallons of water.

If you’re lucky enough to have a physical hydroponic supply store in your town, you’ll be able to find food-grade, high-proof H2O2 there. 

However, it can be tough to find 33% or 35% hydrogen peroxide online because of shipping restrictions on hazardous materials. So you will need to use more hydrogen peroxide at a lower proof to achieve the same effect.

Here are a couple of options from Amazon that we like:

• Pure Life 12% Hydrogen Peroxide
• Viva Doria 12% Hydrogen Peroxide

Dangers of Using Hydrogen Peroxide in Hydroponics

Hydrogen peroxide is a powerful disinfectant with highly caustic properties. This is especially true of the higher-proof H2O2 which is required in hydroponics.

Food-grade H202 can be highly corrosive to soft tissue, especially the eyes and respiratory tract. If swallowed, it can cause serious damage to the internal organs, and in very high exposures, it can even cause death.

So you’ll need to use care when handling high-proof hydrogen peroxide. Eye protection, gloves and good room ventilation are non-negotiable.  

Always store your food-grade hydrogen peroxide in a clearly-labeled container to help prevent any accidental exposures. And be sure to keep it far out of the reach of children or pets. 

How to Safely Add Hydrogen Peroxide to Your Hydroponic System

Hydrogen peroxide has many benefits to offer to your hydroponic system, but only if you use it correctly. 

Here’s how you can get started:

Dilute High-Proof H202 Properly

The first step in introducing H202 into your hydroponic set-up is to dilute the food-grade strength down to an appropriate level.

Whether you’re starting out with 35% or 12% concentration, your end goal is a 3% H202 concentration.

At this strength, hydrogen peroxide is considered safe for human and plant exposure. (But it’s still a good idea to handle it carefully anyway.)

But wait- Isn’t 3% hydrogen peroxide what you can buy at the drugstore? Why not just use that?

A few hydroponic growers report using drug-store H202 with no problems, and whether or not the stabilizing compounds affect plants to a problematic degree remains up in the air.

If you want to run an experiment with drug-store hydrogen peroxide in your hydroponic system, that’s certainly an option. It may do fine!

But the general consensus among growers is that food-grade H202 diluted to a usable strength is superior, for a couple of reasons:

• It totally avoids the potential issue of stabilizers impacting your harvest.
• It’s less expensive in the long run since you dilute it so much.

To get 3% H202, use this dilution guide:

 We mentioned it before, but it’s worth saying again:

When using a high-strength 12% – 35% peroxide, make sure to wear gloves and eye protection and ensure good ventilation. 

How Much Hydrogen Peroxide to Use for Plants

The best way to make hydrogen peroxide a part of your hydroponic system is to introduce a small amount and build up to larger amounts with each change of your reservoir.

First, here’s a chart that lays out the starting dosages, and then we’ll get into the details: 

Standard and Warm Water Tank Dosages

Start by adding 3mL of diluted hydrogen peroxide per gallon of water in the reservoir. For a 5-gallon bucket, that comes out to 15mL; for 10 gallons, it is 30mL, and so on. 

Remember, reservoirs with warm water tend to have an increased risk of low oxygen content and algae growth. So you can safely increase the dosage to 5mL per gallon. 

The oxygen boost and pathogen-killing effects of a standard dose of hydrogen peroxide last about four days. Some hydroponic growers choose to add a half-strength dose each day, or a full-strength one every five days. 

You’ll likely need to do a little experimentation to find out the best schedule for your needs.

Start out with smaller amounts, and keep an eye on your plants after adding hydrogen peroxide. Note any boosts in growth or negative reactions, and adjust accordingly. 

Using Hydrogen Peroxide to Treat Root Rot

If root rot has set in on your hydroponic crop, you may be able to rescue it with hydrogen peroxide if you catch it early enough.

Follow this treatment plan:

1. Remove the net pot and roots of the affected plant from the reservoir.
2. Empty and clean the reservoir, sanitizing it with a 50/50 solution of diluted hydrogen peroxide and water.
3. Add 5mL hydrogen peroxide to a gallon of water, and use this to carefully rinse the roots. If any roots are obviously dead or dying, use sanitized shears to clip them off.
4. Replace the water in your reservoir, and add 15mL of hydrogen peroxide per gallon of water. 
5. Put the roots of your plant back in the water, and observe it carefully in the next few days. 
6. Continue to dose your system with 15mL/gallon daily until you see the root rot resolve. 

What to Do If You Add Too Much Hydrogen Peroxide

Hydrogen peroxide is a weak acid, and your plants could show signs of acid burn if you put too much H202 in your system. This could show up in the form of yellow leaves or stunted growth. 

However, you’d probably need to put full-strength 35% H202 directly in a the water or severely overshoot with your diluted solution to see any problems. 

The starting dose of 3mL per gallon we recommend above is pretty conservative, and some hydroponic growers use far more than that regularly. So as long you’re pretty close to following best practices we’ve outlined here, you’re unlikely to run into any problems.

But if you do notice that your plants don’t seem to be doing well soon after adding hydrogen peroxide, it’s possible that you might have overdosed your reservoir.

The good news: A simple water change will take care of this. All you need to do is empty your reservoir and rinse it out. If your plant had a severe reaction, you can also thoroughly rinse the root system.

Refill the reservoir with water and return the plant to it. Then add the correct amount of hydrogen peroxide, being careful not to overdo it. You can even add a bit less than the 3/mL per gallon dosage to play it safe.

Final Thoughts

Hydrogen peroxide is often used for hydroponics because it does several really important things at once, including:

• Sanitizing the system
• Killing off pathogens
• Boosting oxygen content and overall growth

You can use this addition to make your hydroponic system easier, cleaner, and more productive than ever!

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