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Hydrogen Peroxide and its use in growing

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Hydrogen Peroxide and Horticulture

By Bryce Fredrickson

Hydrogen Peroxide (H2O2) is a clear sharp smelling substance very similar in appearance to water (H2O). Like water it is made up of Hydrogen (H2) and Oxygen (O2), however H2O2 has an extra Oxygen atom in an unstable arrangement. It is this extra atom that gives H2O2 its useful properties. H2O2 has been used for many purposes including cleaning, bleaching, sterilizing, rocket fuel, animal feed treatment and in addition many miraculous claims about its health benefits have been made. This article isn't about any of these; instead it will concentrate on horticultural applications. H2O2 is of great use for both hydroponics and dirt/soilless gardening.

What Does Hydrogen Peroxide do?

H2O2 is an unstable molecule, when it breaks down a single oxygen atom and a molecule of water is released. This oxygen atom is extremely reactive and will attach itself to either another O- atom forming a stable Oxygen molecule or attack a nearby organic molecule. Both the stable and O- forms will increase the level of dissolved oxygen. This is the method by which H2O2 is beneficial. Pre treating the water supply with H2O2will drive out the Chlorine many cities use to sterilize it. This will also degrade any pesticides or herbicides that might be present as well as any other organic matter. Well water can be high in methane and organic sulfates, both of which H2O2 will remove. Many disease causing organisms and spores are killed by Oxygen, the free Oxygen H2O2 releases is extremely effective at this. H2O2 will help eliminate existing infections and will help prevent future ones. It is also useful for suppressing algae growth. The free Oxygen atom will destroy dead organic material (i.e, leaves roots) in the system preventing them from rotting and spreading diseases.

Over Watering

Roots require Oxygen to breathe and low levels are the main cause of almost all root diseases. Both soil and hydroponic plants often fall prey to the same syndrome although it is rarely recognized as what it really is. Hydroponic crops often fail due to "root rot" and soil crops succumb to "over watering." The real cause of both these problems is a shortage of Oxygen at the root zone. In a soil system the soil consists of particles, a film of water on the particles and air spaces between the particles. When too much water is put into the soil the air spaces fill with liquid. The roots will quickly use up what Oxygen is dissolved in the water, if they haven't drunk enough of the liquid to allow air back in to the soil spaces they will stop working. In this situation roots will start dying within twenty-four hours. As the roots die the plants ability to drink water and nutrients will decrease, this will cause symptoms of nutrient deficiencies (mostly pale, slow, weak growth), and strangely they will start to wilt like they don't have enough water. It is easy to make a fatal mistake at this point and add more water.

In a Hydroponic system the cause is a more direct simple lack of oxygen in the solution; this may be from inadequate circulation and/or aeration. High reservoir temperatures also interfere with Oxygen's ability to dissolve in the water. Temperatures above 70F (20C) will eventually cause problems, 62F-65F (16C-18C) is recommended. The same symptoms will appear as with soil plants but you can also check the roots. Healthy roots should be mostly white with maybe a slight yellowish tan tinge. If they are a brownish color with dead tips or they easily pull away there is at least the beginning of a serious problem. An organic, ‘dirt like’ rotting smell means there is already a very good chance it is too late. As roots die and rot they eat Oxygen out of the water, as Oxygen levels are even further depleted more roots die, a viscous circle may be well under way. Reduced Oxygen levels and high temperatures both encourage anaerobic bacteria and fungi. The plants may still be saved but you will have to work fast.

How Hydrogen Peroxide prevents root rot/over watering.

When plants are watered with H2O2 it will break down and release Oxygen into the area around the roots. This helps stop the Oxygen from being depleted in the water filled air spaces until air can get back into them. High Oxygen levels at the roots will encourage rapid healthy root growth. In a Hydroponic system H2O2 will disperse through out the system and raise Oxygen levels as it breaks down. Strong white healthy roots with lots of fuzzy new growth will be visible. This fuzzy growth has massive surface area allowing for rapid absorption of the huge amounts of water and nutrients needed for rapid top growth. A healthy plant starts with a healthy root system.

How to use it.

H2O2 comes in several different strengths 3%, 5%, 8% and 35%, also sold as food grade Hydrogen Peroxide. The most economical is 35% which we recommend be diluted to three percent before using, as at this high concentration it can cause damage to skin and clothing. When working with food grade H2O2 it is very important that you clean up any spills or splashes immediately, it will damage almost anything very quickly. This is extra important with skin and clothing. Skin will be temporarily bleached pure white if not washed cleaned. Gloves are strongly recommended when working with any strong chemical.

Food grade H2O2 can be diluted to three percent by mixing it one part to eleven parts water (preferably distilled). The storage container should be opaque to prevent light from getting in and it must be able to hold some pressure. If three-liter pop bottles are available in your area they are ideal for mixing and storing H2O2. There are twelve quarter liters (250ml) in three liters, if you put in one quarter liter H2O2 and eleven quarter liters (250ml) water in the bottle it will full of three percent H2O2 and the bottle can hold the pressure that the H2O2 will generate. Three percent Hydrogen Peroxide may be added at up to three ml's per liter (2 12 tsp. Per gallon), but it is recommended that you start at a lower concentration and increase to full strength over a few weeks. Use every watering even on fresh cuttings. For hydroponics use every reservoir change and replace twenty-five percent (one quarter) every day. Example: In a 100L reservoir you would add three hundred ml's (3%) H2O2when changing the nutrient. You would then add seventy-five ml's more every day.

Where to get it.

35% food grade: called food grade because it has no toxic impurities. Of course your local hydroponics retailer, whom you can locate over the web.(there may be shipping restrictions on high strength peroxides). The local feed supplier may have it in small towns. Prices range from fifteen dollars per quarter liter to eighty dollars a gallon. One gallon will treat up to fifty thousand liters of water.

3%5%, 8% Can be found at most drugstores or pharmacies, prices start at a less than a dollar for a one hundred-ml bottle that will treat one hundred liters.

What to do if you already have root rot.

In Dirt:

Use peroxide water with an anti-fungicide and a high Phosphate fertilizer (9-45-15, 10-52-10, 0-60-0) for root growth. Or any other product with rooting hormone dissolved in it is helpful in regrowing roots and is strongly recommended. Water heavily until liquid pours out the bottom of the pot. This sound like bad idea, but it flushes out stagnant dead water and replaces it with fresh highly oxygenated water. Don't let plants sit in trays full of water, the soil will absorb this water and stay too wet. Don't water again until the pot feels light and the top inch or two of the soil are dry.

In Hydro:

Change your nutrients. Add H2O2 to the system. This will add oxygen and chemically eat dead roots. If roots are badly rotted and can be pulled away by hand you should pull them off. They are already dead and will only rot, causing further problems. Add a fungicide to kill any fungus that is probably present in the rotted tissue to prevent it from spreading. Increase aeration of the water, get an air pump and air stones, or more of them, for the reservoir. An air stone under every plant is usually very effective, but will require a larger air pump. Models that will do from forty to four hundred stones are available. Decrease the reservoir temperature, oxygen dissolves better in cold water and disease causing organisms reproduce slower as well. A good temperate range is 62F to 65F; anything above 70F will eventually cause a problem. It is also a good idea to remove any wilty plants from the system and put them on a separate reservoir so they don't infect plants that are still healthy.


The key to big productive plants is a big healthy root system and Hydrogen Peroxide is a great way to keep your roots healthy. It is a must to ensure the biggest best crops possible and to increase the chances of your plants thriving to harvest. Peroxide users will rarely lose plants or crops to root disease and will harvest larger and more consistent crops. Additional info

How much to add

US Standard

1.28*G/C= Liquid Oz's per day


10*L/C= Ml per day

C= % concentration of H2O2

L= Number of liters in reservoir

G= Number of Gallons in reservoir

Example: How much 3% H202 should I add to 7 gallons of nutes?

1.28*7/3=2.986 Oz's each day.

Hydrogen Peroxide breaks down to hydrogen and oxygen within 3 days of being added either to a hydroponic solution or a soilmix. There is no residual with it, it becomes oxygen and hydrogen gas. It is not un-natural in the least, it forms the basic building blocks of life, its just a stable liquid form of oxygen.

The additional chloroplastic activity as a result of the chlorophyll deeping will give you much thicker stems and larger leaves, with much deeper green. Yes the plants can absorb more light. the solution will also be much cleaner as the organic matter is oxidized to make...oxygen

happy growing,


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So I did the math and for me is: 3ml / L, since I have a 3% H2O2.

But with this rate, what efect will it have in the benn bacteria and funghi we have in the medium? Will the h2o2 kill them? If so we cant use it everywatering... Maybe it should be used only wen we suspect or know there's a root problem or for prevention wen flushing.. I used it daily with my other plant that had a bunch of problems, but stopped with the continuous use of it since I read it could kill the good organisms, even harming some organics of the nutrient solution. I bought un enzyme called "Hygrozyme" that is told to be the best one wen talking of what a enzyme should do, and fortunately she was designed to be h2o2 tolerant and can be used with very good results in flushing wen combined: Hygrozyme + H2O2.

Can you enlight us about this, if the h2o2 can harm the organics of the nutrient solution, the benneficial bacteria and funghi at any rate of % and especialy at this lower rate I'm using of 3%?

thank you and take care, my friend!

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I was entertained by the info you have provide for us to read.I went to the drug store and purchest 12% H,peroxide did the maths and iam sure i should mix it 0,75ml / L .I would multiply it by 20 =15ml /20L .Will start off 5ml/20L and buld up slowly.Any info on my doings would help, not to sure if iam correct or not .Can not afford to lose my babies at the moment.

Do you use or know of people that use it .

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Thanks for that drunkkuckelhead ,i will go and try find food grade h.peroxide some things are hard to get where iam from.My plants are not sick so iam not in such a rush but this looks like something that is needed to be addid to my op.Thanks again for this info.

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Hi i dont realy antherstand if its goed or not for soil some people say is not goed for benefical bacteria other say is goed and  is that the wonder product to prevent budrot ? And for germination 3% 3ml / L water its not very clear cause they say to start whit a low dosage 😵

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So i think i find what i search use at 0,1% /l for germination and not use it on organic grow but iam not sure for that and i dont realy understand what i read on the effect to botrytis 

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Hi g22


I have been checking out this hydrogen peroxide.


For use in soil from what I read on a grow jourrnal by @ShaggyGrower it looks like it kills the bacteria that don't like oxygen and benefits the ones that do like oxygen, it also helps to protect the roots as well as killing bugs like gnats that live in the dirt and lay eggs.


With germination I would put 3 ml of 3% into a glass of spring water or plain tap water, as soon as they sink remove the beans and place them onto damp kitchen roll, use just spring water or plain tap water to dampen kitchen roll and to keep it nice and moist.


For watering and feeding the original poster recommends 3 ml of 3% per litre of water, this seems to be what people are using in their grows, setting off at 1ml per litre and slowly increasing to 3ml per litre as the plant grows.


I got 200 mls from a local chemist that is 9% so I will add 600 mls of water to make it 3% giving me 800 mls so it will last a while, I suppose I could make smaller batches instead.


With the bud rot and mill dew it seems to be very effective, people seem to put a few tea spoons into a litre and use it to spray on the plant, the question here is how big is the tea spoon? It would make it easier if the amount of H202 was in millilitres it would be more accurate and less of a guess and a leap of faith.


It is definitely something to have handy to deal with bugs and bud rot even if you don't use it as part of the watering and feeding.


We just need more knowledge, it would be good if others who have experience would tell us how they use it in their grows.



Likkle more

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Thanks for the info 

I find a goed info about the use of peroxide i need to search i don't find it  back.

not goed for a bio or organic , that kill the goed bacteria is only goed in last solution if you problem with the roots 

That desinfect and kill all the fungy good and bad and all dead material dead roots and give withe roots and oxigene is good for hydro and desinfect /eliminate alga in watertank 

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Hi @g22

Like you I am trying to make sense of how to use Hydrogen Peroxide and if it has any real value.

I agree really for dirt it is best to only use as a foliar spray for bugs, but for hydro growers it is their friend and does good.

I found some useful information on the Grow Weed Easy site by using the search term "hydrogen peroxide" and I got the results at the link below.

https://www.growweedeasy.com/search-results?keyword=hydrogen peroxide


I think it is better to use products or things to help create a healthy vigorous root zone and help friendly bacteria thrive.


The Green House Feeding from what I have seen in test grow journals helps good bacteria thrive in the dirt, I have just bought some Plant Magic Oldtimer Organic Granules that provide good bacteria, apparently 20 different types and it helps to maximise root growth and provide disease resistance.




I will keep the 200ml bottle of 9% hydrogen peroxide I bought just in case it comes in handy to deal with some bugs, but otherwise it will stay in the bottle.


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Hi gasman last week i give 150ml to 50l  water .

 my water reservoir have some green alga i was reading that h2o2 kil all the alga in 24h.

after 4 day nothing change the alga are always there maybe i don't use right amout of h2o2 and my bottel is at 3% 

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Hi @g22


WOW that is strange I think you may be right about the strength of the solution.


Hopefully some one with experience will provide some useful info about the best strength or percentage to use to get rid of algae in a hydro grow.

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They talk about HP 35% to clean a Room if i good remember but you Need a autorisation to buy it With all the terrosit its no more sell to all the people.

To kill alga in a réservoir or in a littel pond With fish i read you Can use the HP 3% i know They use HP in swimingpool too but its a expensive système to eliminate the  use of chlorine.

For m'y tent i use chlorine to désinfection but its no good for your lung 

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