Hydrogen Peroxide (H2O2) 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 negatively charged Oxygen atom that gives H2O2 its useful properties. H2O2 is 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 faq focuses on its use in 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 (O-)and a molecule of water is released. This oxygen atom is extremely reactive and will attach itself to either another Oxygen atom (forming a stable O2 molecule) or attack a nearby organic molecule.

H2O2 will rapidly eliminate the Chlorine used in many municipal water supplies, as well as degrade any pesticides, herbicides or other organic matter that might be present. Well water is often high in methane and organic sulfates, both of which H2O2 will remove.

Both the stable and O- forms will increase the level of dissolved oxygen. Increasing the DO in your nutrient solution will benefit the root system and be detrimental to harmful anaerobic bacteria such as pythium.

Many disease-causing organisms and spores are killed by the free O- atom. The free Oxygen atom will destroy dead organic material (i.e., leaves and roots) in the system, preventing them from rotting and spreading diseases. H2O2 will help eliminate existing infections and will help prevent future ones. It is also useful for suppressing algae growth.

Over Watering

Both soil and hydroponic plants often fall prey to the same syndrome. Hydroponic crops often fail due to “root rot” and soil crops succumb to “over-watering.” The actual cause is a shortage of Oxygen at the root zone, allowing a Pythium infection to take hold.

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 the dissolved oxygen within these pore spaces. If the root system has not absorbed the water within these pore spaces, air will not be able to enter and Oxygen within that space will become depleted. In a low oxygen environment, roots will begin dying within twenty-four hours.

As the roots die, the plant’s ability to uptake water and nutrients will drastically decrease, and the plant will show symptoms of nutrient deficiencies (pale leaves, and slow growth). Plants will start to wilt (appearing water deficient) – at this point many growers will mistakenly water their plants!

In a Hydroponic system,

oxygen deprivation is often caused by high temperatures and inadequate nutrient circulation and/or aeration. High reservoir temperatures interfere with Oxygen’s ability to dissolve into water. Temperatures above 70F (20C) will eventually cause problems, 62F-65F (16C-18C) is recommended.

Oxygen deprivation symptoms in hydroponics are similar to that of soil – but at least you are able to 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 remove Oxygen out of the water; as Oxygen levels are depleted even further. more will roots die – a viscous circle!. Reduced Oxygen levels and high temperatures encourage anaerobic bacteria and fungi, which attack the plant further mercilessly.

How does Hydrogen Peroxide prevent root rot & over-watering

Plants watered with H2O2 will experience extra oxygen in the root zone when the peroxide breaks down. 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 systems, 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/apply 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. When working with food grade H2O2, it is very important that you clean up any spills or splashes immediately, it will damage almost oxidize everything very quickly. 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 3 ml’s per liter (2 1\2 tsp. per gallon), but it is recommended that you start at a lower concentration and increase to full strength over a few weeks.

For hydroponic applications, use every reservoir change and replace twenty-five percent (one quarter) every day. Example: In a 100L (25gal) reservoir you would add three hundred ml’s (3%) H2O2 when changing the nutrient. You would then add seventy-five ml’s more every day.

[Editor’s note: high concentrations of H2o2 can be detrimental to organic additives (such as beneficial additives) and organic nutrient mixtures.]


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.

Where to get it

35% food grade is called “food grade” because it has no toxic impurities. Of course your local hydroponics retailer or web stores have it (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 Soil:

Use peroxide water with an anti-fungicide and a high Phosphate fertilizer (9-45-15, 10-52-10, 0-60-0) for additional root growth. Or any other product with rooting hormone dissolved in it is helpful in re-growing roots and is strongly recommended. Water heavily until liquid pours out the bottom of the pot – this method helps flush 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 Hydroponics:

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 cut 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 reservoir – add air pumps and stones. An air stone under every plant is usually very effective, but will require a larger air pump. 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 wilting plants from the system and put them on a separate reservoir so they don’t infect plants that are still healthy.


The key to productive plants is a healthy root system; 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.