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 and Oxygen, 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.
1. 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. Pretreating the water supply with H2O2 will 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.
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 colour with dead tips or they easily pull away there is at least the beginnings of a serious problem. An organic dirtlike 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 viscius 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.
3. How Hydrogen Peroxide prevents root rot/overwatering.
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.
4. 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 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. 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%) H2O2 when changing the nutrient. You would then add seventy-five ml’s more every day.