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This is a very good question. Hydrogen Peroxide (H2O2) has been used in hydroponics and indoor gardening for some time now, with a wide range of results. Typically it has been diluted to plain water or diluted and applied with nutrient solutions.

H2O2 has the potential to use the additional, unstable second oxygen molecule to boost higher oxygen levels in the root zone to help increase growth rates and yields. The oxidative action of the unstable second oxygen molecule is also useful in treating and preventing certain types of bacterial and fungal diseases, particularly in the root zone.

It sounds like H2O2 would be a very beneficial product to use with all feedings and nutrient applications. However, in reality this is simply not the case. The oxidative effects of H2O2 are very powerful. Coupled with the fact that the oxidative action is non-selective, the powerful effects of additions of H2O2 will break some very important chemical bonds in your nutrient solutions, rendering a large percentage of critical nutrients unavailable to your crop. Nutrient lockouts can hurt your crop and cost you yields.

Beneficial microbial life in the root zone, growing medium and reservoir are also seriously harmed by the powerful oxidative action that adding Hydrogen Peroxide creates when added to the nutrient solution or when applied with just plain water to the growing medium and root zone. Beneficial fungal and bacterial microbes help to improve the health, growth rates, quality and yield of your crop. These may occur naturally in many organic based growing mediums, or may occur through inoculations of bacteria and fungi specific products added by the grower.

So, when is a good time to use Hydrogen Peroxide? If germinating seeds or starting cuttings in an inert material such as rockwool, you can pre-treat the medium with a dilute solution of H2O2 several hours before any nutrients or plant material are added. Also, H2O2 is very useful in sanitizing growing systems and water to be used for nutrient solutions before nutrients, additives and beneficials are added to the mix. If H2O2 is given sufficient time to react with water and growing surfaces it can be beneficial. Typically, you should allow at least a few hours to pass before adding any nutrients, additives, or beneficials to water that has been treated with H2O2.

Firstly, during the initial reaction with the H2O2 to water in the reservoir and/or growing system, any bacteria or fungi that may potentially cause diseases will be oxidated/destroyed. This provides an efficient way to further sterilize water and growing systems. The additional benefit is that the Dissolved Oxygen (D.O.) levels in the treated water may be slightly elevated after most of the oxidative reaction between the Hydrogen Peroxide (H2O2) and any impurities such as fungi or bacteria in the Water (H2O) has occurred.

In the event of severe damage to individual plants or even entire crops due to pathogens in the growing medium or root zone, growers may consider trying an application of active H2O2 to the growing medium as a last effort before pulling the plug and starting a replacement crop. When H2O2 is applied with plain water to the growing medium/root zone just after being diluted, the oxidative effect of the active H2O2 may kill off the pathogens and leave the crop standing to possibly recover with some TLC from the grower. Again, this should be regarded as more of a last resort rather than a first line of defense, due to the fact that the nutrients and beneficial life in the growing medium and root zone will be destroyed. If H2O2 is applied at too high a dosage rate or the plants are particularly sensitive, H2O2 can damage or even kill the crop.

By exercising a degree of caution and understanding the ins and outs of the oxidative nature of the product, Hydrogen Peroxide may have a place on your shelf of growing supplies for pre-treating water, cleaning and sterilizing growing systems and surfaces and as a last resort for the treatment of root diseases.

Cheers
Erik Biksa