I haven't used it for watering or as a preventative. I use it if I want to clean the leaves of a plant or plants or if I have a fungus or some kind of crude that frequently grows on certain of the mounting woods I use. I also use it when i have a new growth that damps off. I did just go out and check the nigro-hirsute dendrobium I sprayed a while back. The leaves didn't seem to like it. They are a bit mottled and yellow. A good reason to not do the whole collection.