Ive heard of people doing it, but a little bit differently than how you're delivering it. What Ive read up is adding H2O2 to the water so that the extra oxygen breaks off of the H2O2 more readily or quickly. Usually even less than one cap full per gallon, and then letting the gallon sit out for like 30 minutes to an hour before watering. I wouldn't recommend adding H202 straight to the roots like that. Think about it. H2O2 is used to kill bacteria, good or bad. Your plants need lots and lots of bacteria to help keep the soil healthy. Just throwing it into the soil is the same thing as having a cut and throwing H2O2 on it to kill the bacteria and you get that nice sting. Who knows, maybe it stings for them too.