Answer: Hydrogen peroxide could theoretically help with aeration of the soil and has some disinfectant qualities as well. (For example, some hydroponics gardeners add it in small amounts to the water in their system to increase aeration and reduce growth of harmful pathogens in the system.) So it might help a plant that has been in overly wet soil to some extent, however too much could damage the tissues and tolerances vary by plant so there is a risk of damaging the roots. It would not be something commonly done.
If you are having trouble with root rots, you would need to change your watering habits or possibly change the soil mix the plants are growing in so it does not stay wet for prolonged periods. If it is a problem in the garden, you would need to change your drainage patterns to dry the area out, or adapt your plant selection to those that actually thrive in wet soil.
Too, some root rots are disease problems that persist in the soil and will infect new plants if they are susceptible, so again, changing the plant selection would probably be a better solution to the problem. Rhododendrons for instance are commonly affected by this type of problem and especially if grown is soil that is not well drained.
I hope this helps.
Q&A Library Searching Tips