I think it was GanjaGed who posted an article on H2O2 recently: you might read this and try it:
Peroxide helps heal sick plants
In particular, a peroxide is a great option for treating root rot. If your soil is too compact, root rot can develop. Use 3% hydrogen peroxide mixed with water (one part peroxide to two parts water) and pour it over the infected roots of your plant.
Nix mold and mildew with peroxide
Moisture, dirt, and heat can combine to create some nasty mold and mildew situations. Get rid of mold and mildew by mixing 10 tablespoons of hydrogen peroxide in a liter of water and spray daily until the mold/fungus goes away for good
Treat your water with hydrogen peroxide
Make the water you feed your plants a little healthier, by adding a bit of peroxide with the water in your watering can before applying to your plants and lawn. The peroxide removes chemicals and pesticides from tap water, making it healthier for your plants.Â
Peroxide works as a rooting agent
The key to a strong, healthy plant is a good base (the roots). Give your roots a boost by dosing them with a little bit of peroxide. This can also help revive limp leaves. Spray a peroxide/water solution into the solution into the soil around the plant.
Peroxide keeps bugs away
Skip expensive chemicals at the store and spritz your plants with 1% hydrogen peroxide to keep bugs at bay.
Peroxide can prevent infections on cut plants and trees
Treat infections on plant leaves or roots with a spray of water and peroxide to disinfect the area and prevent the disease from spreading. You'll want to douse the area with a lot of the water/peroxide solution for the best results.Â
Peroxide help seeds grow faster
You can speed up the growth of seeds by soaking them in a weak solution of water and peroxide for a few minutes before rinsing and planting.