David,
Hydrogen Peroxide (H2O2) is not stable so naturally breaks down into water and oxygen. A little H2O2 in water releases oxygen and helps oxygenate the water. A lot of H2O2 works as a bleach (think Peroxide Blond) and would destroy the roots.
If you are trying to keep plants watered while you aren't there to take care of them, try using an old plastic container (milk jug, water bottle) with a wicking system or a dripper inserted. You can also use a bucket as a reservoir and run lines to your plants.
Daisy
