Hydrogen peroxide 3% solution -the type you buy in almost any grocery store or drug store- is a fantastic fluid! What other thing can you name that can be synthesized or can occur naturally, and is a precursor to -and a by-product of- almost ALL cell growth on earth (look up 'oxidative metabolism' and 'catalase peroxidases') but can also be deadly to cells? Something that can “disinfect” like chlorine but not persist in the environment like chlorine? A compound that can actually add oxygen to a plant's roots? A compound, that when combined with other compounds, can assist in delivering nutrients to your plants (a subject for a much later blog)? Whoa!
When I swish my mouth with H2O2 I am removing a dead layer of cells in my mouth and I'm also killing any free bacteria or fungi that is colonizing my mouth. Why is it killing that stuff? That extra oxygen atom that's so easy to break off, also known as a free radical, absolutely loves to attach to anything that will accept it. The white foam is oxygen reacting with an enzyme. Boom! The free radical oxygen reacts very quickly with the catalase enzyme in the cell and creates water, oxygen, and heat. It happens very quickly and leaves little or no residue that is harmful to me; just a mouth full of icky dead cells that I wash out. Instant bad bacteria doom. Sort of.
Here's the problem, and this is the problem everyone who uses H2O2 in hydroponics faces: How much or how little should I use? Almost all cells, including root cells, create catalase. It is the cell's defense against natural H2O2 when it is produced during oxidative metabolism. Remember in part one I mentioned the Krebs and the Calvin cycles? That is oxidative metabolism or cellular respiration! Catalase actually exists for breaking down H2O2 into water and oxygen. That is a cell protection feature, but you'll be using that reaction to add oxygen to your plants and to clean your reservoir by overwhelming the enzyme.
Yes, H2O2 will kill ALL bacteria, algae and fungi in your nutrient reservoir. It will also kill some root cells. It is not selective. But Jim, don't plant roots need beneficial bacteria? Yes, although the function of bacteria in waterlogged plant roots doesn't seem to be well-understood. I believe there is a bacterial nitrogen-fixing mechanism different than the many other bacteria found in soil. I also believe there is an alternative oxygen-delivery system, working within my liquid-fed plant roots, that I don't fully understand. As I've said before, I should not be able to grow eight to ten-foot tall tomato plants, huge collard greens, and softball-size green peppers in a reservoir the size of a milk jug and only using a half-gallon of nutrient solution!
I love to experiment. I have killed a fair number of plants by using too much H2O2. Conversely, I have watched nutrient reservoirs become overrun with bacterial mats and fungus blobs, especially during periods of high heat because I didn't use enough H2O2. Here comes my disclaimer: Virtually everything I do is a little off the beaten path. Most of it is experimental. Since my specific systems didn't really exist before, I used other experienced growers' anecdotal information and worked from there to create the systems and then the methods to grow and protect the plants. You can under-dose, correct dose, and over-dose your plants. You have been warned!
My trial-and-error results are what works for me. You will have to read up and then grow stuff until you've grown enough to know what works for you. There are many variables: temperature, reservoir size, types of nutrients and concentrations, rate of circulation and nutrient fluid change-out intervals.
In the one-gallon milk/water jug-based Plain 2 Grow Systems, you'll typically maintain the nutrient solution at about the half-way point, or a half-gallon of nutrient solution. My You Tube videos state a nutrient level of up to 2+ teaspoons of each of General Hydroponics Flora Grow, Flora Bloom, and Flora Micro series to one gallon of water. I add approximately one-half ounce of H2O2 3% to the water and the nutrients during the initial mixing. The H2O2 will remove the chlorine if you are using city/ tap water and will kill biological agents in well water. I will then add about one ounce of hydrogen peroxide at each fluid change (about one week intervals). I've found this to be my best practice for most plants.
In my experience, my plants showed some slight negative reactions (curled leaves and droopiness) for a day or so and then they seemed to put on a growth spurt and then became greener. Those negative and positive reactions could have been a coincidental response to some other variables. The H2O2 never fully cleared the solution of bacteria or algae but kept it under control. I believe that the roots adapt very quickly to a sudden influx of oxygen and will quickly regrow certain bacterial colonies. I have created some experimental foliar feeding mixes which include H2O2. They have worked well.
Some growers, myself included, have used chlorine bleach (sodium hypochlorite 8%) instead of H2O2 and have had mixed to good results. In a future blog I will discuss an accidental useful discovery about bleach and hydroponics. It is possible when using bleach by itself, however, to create some interesting and possibly unwanted reactions such as chlorine gas, hydrochloric acid, amines and metal halides. Chlorine reacts with some metals, like iron, to form salts like iron chloride. Whether or not this makes iron and other metals available or unavailable (chelation) to the plant is unknown. That's an area I'm still researching and learning about.
Don't be afraid to use hydrogen peroxide 3% in small quantities to add oxygen to your plants. Using the quantities I've described is just a suggestion based on the experiences of myself and others. You are ultimately responsible for your plants and your own health and safety. There is a lot of scientific and field evidence to support the use of H2O2. Take your time and apply the doses slowly and additively and discontinue its use if you are seeing unwanted results.