Growing seedlings for the garden or growing plants in containers, can often be fustrating because of problems with die offs from overwatering, soil fungus, and rotting roots. Overwatering is one of the main reasons for plant deaths be it tender tomato seedlings or potted palms. Using common medicine cabinet hydrogen peroxide, it is possible to save plants from overwatering deaths as well as protect them from fungal and bacterial diseases.
Hydrogen peroxide is a highly reactive chemical that has a molecular structure similar to water in that it is made up of only hydrogen and oxygen, but its formula is H2O2 giving it an extra oxygen atom. It is this extra oxygen that makes it so reactive and so beneficial for plants. Plants need oxygen to survive, especially in the root zone. If the soil they are growing in becomes saturated with water, the roots cannot absorb the gaseous oxygen that the plant needs. Without oxygen the plant's roots will start to die and rot, leading to the death of the plant. The oxygen released by HP will react with any organic materials and cause them to breakdown, thus releasing nutrients into the soil. HP will also kill fungus, mold, and mildews that can cause plant diseases.
By using a solution of hydrogen peroxide when watering plants, they can be provided with a boost of oxygen right where they need it around the roots. There are different strengths of hydrogen peroxide from 3% up to 35%. The watering solution described here uses 3% HP, which is the most common type sold in drug stores. If you use a stronger HP solution, you will have to dilute it down to a 3% solution and then follow the guildlines given here. Higher strength HP can be dangerous with 35% HP being able to burn the skin and stain surfaces like bleach. Besides making the plant roots healthier, misting plant leaves with a HP solution can fight diseases that strike them such as black sooty mold and powdery mildew. Plant seeds that need soaking to speed up their sprouting can be treated with HP to sprout even faster and to produce even healthier plants.
Use the following guidelines to make hydrogen peroxide treatments for keeping plants healthy. Once mixed up the solution should be used right away to be beneficial.
Root treatment - Mix 1/2 cup of 3% hydrogen peroxide in each gallon of water and use to water plants. If your plants are already showing signs of being overwatered, then drench them with this solution and let dry till the pot fills light before watering again.
Leaf mist - Mix 1/4 cup of 3% HP per gallon of water for seedlings and plants having young tender leaves and use up to 1/2 cup per gallon for tougher leaved plants. This spray used daily will prevent molds and mildews from growing on the plant leaves.
Leaf spray for diseased plants - For plants that already have powdery mildew or black mold problems, use 1 cup of 3% HP per gallon of water at a treatment. I have used up to 4 cups per gallon for waxy leaved plants like gardenias or citrus, to fight black sooty mold that grows on them.
Seed treatment - For hard seeds that sprout best after soaking, prepare a solution of 1/2 cup of 3% HP to a gallon of water to soak them in overnight.
Killing weeds - Spray weeds with undiluted 3% or 5% HP to kill them by bleaching the leaves. Don't get it on any plants you don't want hurt and at this strength it will only burn back the tops of stronger plants though it will kill them with repeated use. A 10% HP solution will kill plants down to the roots when used as a soil drench.
If you want to prepare your own 3% hydrogen peroxide solution from the stronger 35% HP, you will need to dilute it using 1 part 35% HP to 11 parts water. Wear gloves and eye protection when working with 35% HP and wipe up all spills immediately. Use water that is free of chlorine as the HP will react with the chlorine and be of little benefit to the plants. You can mix 1 cup of the 35% HP to 11 cups of water to make the 3% HP solution or you can mix one ounce to 11 ounces of water to make 12 ounces of the 3% solution. Store any HP solution in a dark cool place as light will cause it to degrade quickly. Mark any container clearly because of how HP resembles water. Hydrogen peroxide can be deadly if taken internally in too strong a solution.