I've used a diluted mix of 35% food grade HP for putting on vegetable starts, it works great. I read a few years ago that when rain falls it picks up oxygen molecules and falls as HP, it seems as though that makes grass so green in the spring. I haven't figured out how food grade HP is used, my guess is it's used to clean food processing equipment. By the way I've seen the 35% stuff burn a hole through leather, so if you ever get a hold of high percentage HP, handle with caution. The really high percentage stuff, around 100% is used as rocket fuel.