Hydrogen Peroxide For Hydroponics: Beginner’s Guide

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A hydroponic grower holds a bottle of nutrients to feed to lettuce

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.

RELATED: Looking for more beginner-friendly hydroponics information? Check out our post on on Deep Water Culture basics!

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.

RELATED: A good air pump is another essential component to raising oxygen levels in your hydroponic system. We wrote a post on our favorite air pump choices, so stop by to learn more! 

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:

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:

Chart listing the proper dilution ratios for food-grade hydrogen peroxide for hydroponics.

 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: 

Chart showing different dosages of hydrogen peroxide in hydroponics.

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.

Frequently Asked Questions about Hydrogen Peroxide for Hydroponics

About four days. You can either add hydrogen peroxide to your hydroponics system on a daily basis in small amounts, or renew the full dosage every four to five days for maximum benefits.

Don’t mix hydrogen peroxide with vinegar–this creates an even more corrosive compound called peracetic acid.

While you can mix hydrogen peroxide with baking soda for cleaning purposes, don’t try to store this mixture. It can expand rapidly and explode containers.

Absolutely not! Nutrients in hydroponics are inert substances, not living ones. H2O2 targets living organic organisms and has a very specific and limited chemical reaction with water. It has no reactivity with hydroponic nutrients.

But don’t use hydrogen peroxide in a system with beneficial microbes, as these will be attacked and killed by H2O2. Also, most aquaponic growers avoid using hydrogen peroxide in their systems as well. 

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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  1. Hi, i was wondering is alright to leave the diluted h202 in water reservoir? Some of the gardener mention the plant die after doing this. So they only rinse the root for around half and hour or 1 or 2 hours (lot of discrepancy) and change the water with fresh water. Im confused which method to go as im growing vegetable and the root are covered with algae.

  2. Hi Nimerk, great question! Yes, it’s perfectly fine to pour your diluted H202 right into the tank and leave it there. The chemical bond in H202 is weak and it will break down into its basic elements of hydrogen and oxygen rapidly, so that’s why you have to add more to your tank every few days. I can’t say with certainty why the plants for the other gardener died, but it’s possible that they didn’t dilute it properly. As for your plant roots covered with algae, I recommend that you follow the steps for using H202 to treat root rot as described in the article. That’s a pretty effective strategy for most cases of algae. Best of luck, and thanks for reaching out!

  3. does the peroxide daily dosage that you recommended affect the organic molecules in the nutrient solution, like vitamins, amino acids, chelated metals, enzymes, khelp extract ? You argue it kills living organisms, and I agree, but do you think it also attacks the other molecules (that are not inert nutrient salts) ?

  4. Excellent question, John! Fortunately, hydrogen peroxide has no negative impact on nutrients when administered in the proper dosage. You’d have to put in a pretty massive amount of H202 before you ran into any problems with nutrient integrity, and you’d likely see chemical burns on your plants before then.

  5. Cant i mix h202 in my reservoir with my water and nutrient and lower the ph of my solution with white vinegar .will it still produce peracetic acid if the h202 already dilluted in the solution ?

  6. Hi Steven, that’s a good question. I’ve never personally tried it- I know that H202 breaks down quickly into its basic elements in water, but I can’t say for sure whether/when it gets to the point that it won’t react with vinegar anymore. You would probably be better off sticking with a commercial pH down product, which usually seems to produce better results over the long term than vinegar anyway. Hope that helps, thanks for asking!

  7. Erinn this is beautifully written and probably some of the best info I have found about H202 in hydroponics on the web after MUCH searching. (btw, the person who posted videos of H202 killing plants is wrong and clearly has a different problem). My experience with H202 is exactly as you have outlined here in a very clear and concise manner.

  8. Thank you so much, Mike! I’m glad to hear that the article was helpful, and I really appreciate you taking the time to let me know. I hope your hydroponic growing continues to go well!

  9. When you say how much to use in the reservoir is the volume you refer to the volume of the reservoir or the volume of the whole system. My reservoir is 15 litres but my system hold 75 litres so how much diluted hydrogen peroxide should I use?

  10. Hi Mary, all our dosage guidelines are per reservoir, so you would add the H202 to each individual one in your system. 15 liters is just shy of 4 gallons, so you would 12 mL per reservoir for a standard starting dosage and adjust it up or down as your situation calls for. If you dosed all your reservoirs at that starting point, you’d use a total of 60 mL in your entire system. Hope that helps, and thanks for asking, good question!

  11. Great article! I unknowingly put regular, drug store, h202 into my hydroponics system…. how bad is that? i’m new to all of this.

  12. Hi Shannon, good news- drug-store H202 likely won’t cause any problems in your hydro setup. It just won’t have the beneficial effect that a purer, stable food-grade product does. So don’t worry, you haven’t harmed your plants, but you’ll want to invest in better H202 to get the results you’re looking for. Thanks for reading, and glad it was helpful for you!

  13. Erin
    I don’t want to leave the gallon of 35% as is. If I dilute it into 4 gallons of 12% will that diluted mixture last as long as the original 35% mixture?

  14. Hi Eddie! No, diluted H202 does not have the same shelf life as an undiluted bottle. Once H202 mixes with water, it tends to break down pretty quickly, so I wouldn’t recommend pre-diluting a large quantity. That’s a really great question and I’m glad you asked!

  15. Welcome . When placing hydrogen peroxide in the nutrient tank, do I start the pump immediately or how long do I wait for the pump to run until the peroxide decomposes, knowing that I use the dutch backet system filled with volcanic stone

  16. To treat root rot, how much hydrogen peroxide is added per liter of water.. but I cannot take out the roots and clean the rotten roots because I am planting in a shower. I cried a volcanic stone… What is the procedure in this case, thank you….
    I have another question, how often should I water my crops and how long should each irrigation take to avoid rotting the roots? Thank you

  17. Hi Mohammad, you should be fine to have the pump running continually while adding the H202 and after. As far as I’ve ever been able to tell, H202 shouldn’t react badly with any minerals, especially when it’s so diluted in your entire system. Hope that helps, thanks for asking!

  18. Hi Mohammad! If you can’t take the affected plants from the system, I would remove the bucket with the affected plant(s) from the system to prevent spreading the disease. I would also treat the entire with at 5 mL H202 per gallon to hopefully keep the other plants healthy. Keep a close eye on them for any signs of disease!
    For treating the root rot, you want to use 15 mL per gallon; 1 liter is equal to 0.26 gallons, so you’d be looking at 3.9mL per liter.
    You mentioned earlier that you have a Dutch bucket system. The watering frequency depends on which plants you’re growing- some plants demand more nutrients/water than others. So it’s a bit of trial and error to get that balance right. A good place to start is setting the timer to water the plants for about 30 minutes three times every day. Watch how your plants respond, and water more frequently if needed.
    I hope this helps you out, and best of luck treating your plants!

  19. Welcome
    To treat root rot, do you add hydrogen peroxide to the water only and dip the plant in it, or do you add it to the nutrient tank … There is a question that says whether adding peroxide directly to the tank and with a solution weakens its concentration due to the interaction of the elements of the solution with peroxide. What is your opinion?

  20. Hi Mohammad, you can add the H202 directly to the tank to treat root rot. If your plant has a very serious infection, taking it out of the system and treating it with a stronger peroxide rinse is an option, but I would only try that if the plant wasn’t improving with tank treatment. As for your second question, I’m not sure I completely understand. Which elements are you concerned about with the H202? As far as I’ve been able to find out, the only concern is the potential for reaction with vinegar, so I don’t recommend using that with H202. Otherwise, I’m not aware of any other elements that can react with or weaken H202. Hope that helps, thanks for asking!

  21. Thank you for your responses. Is peroxide possible to save the plant in case of complete wilting? .. When using peroxide, how long does it take in hours to produce new roots to judge that the plant is not dead yet?
    I bought hydrogen peroxide with a concentration of 6%, but I doubt that it is adulterated and its concentration is much lower, as it accidentally touched my finger and no white spots appeared at the place of contact. .?
    Thank you very much in advance

  22. Hi Mohammad, unfortunately, there are cases where the disease has progressed so far that the plant will die even if treated with H202. If it was me and the plant is in that bad of shape, I would honestly be very aggressive with the H202. Isolate the plant (whether that means taking it out of the tank or disconnecting the tank from a larger recirculating system) and add extra peroxide to see what happens. If nothing else, you can learn for the future from your experimentation.
    For a timeframe for when you might see new roots, it would likely be at least a few days to potentially a couple of weeks. I would be looking for better color and tone in the existing leaves first.
    Is your 6% H202 food grade? That’s the only way to ensure that there are no fillers or stabilizers added to the actual peroxide. The label should say “food grade” if it is, and the ingredients list may also say “stabilized” if that’s the case.
    I hope your plant recovers! Thanks for asking your questions!

  23. I used Kratky method, or using boxes. Is good to mix hydrogen peroxide at the same time with nutrient solution?

  24. Hi Randy, this may be personal preference here, but I would set the Kratky system up and let it get established for a couple of days. Then I would begin adding the H202 periodically over the growing cycle. Hope that helps- thanks for asking!

  25. HI Erinn,
    Thanks for this info, it’s the best summary I have found and man have I looked!
    I have an Aerogarden which seems to be a perfect breeding ground for root rot!
    Your instructions are super clear and I have been giving them 15mls per gallon (2 in tank) for the past 3 days and now I am seeing fresh new roots emerge!
    Once the smell is gone and the roots are healthier I would like to move to an inoculant like Hydroguard but I know H202 will kill the good bacteria too. How long would you wait before adding good bacteria?
    A full 4 days?

  26. Hi Mike, I’m glad you found the post helpful and that you’re seeing good results. Yay! I haven’t personally used Hydroguard (or similar products) myself in my AeroGarden, but I would probably err on the safe side and wait the 4 days. You probably don’t have to since H202 breaks down pretty quickly, but that would be a “why take the chance” thing for me. Thanks for the question, and I’m so happy your plants are doing well!

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