I would assume it would make it too acidic. And I would think espresso would be better since the coffee is stronger. Maybe its all in the coffe and the grounds are all used up. Heck I dunno. Why don't you just go to lowes and buy some slug bate. There is some that is harmless to dogs and animals. It is a few bucks more, but it works good. It got rid of my snail problem. spread it out about every 2 weeks or so because the stuff doesn;t last that long. The pellets start to grow mold and stuff when they get wet over and over like in a GH. A bag lasts a good while. Also if you insistant on using it on your plants try a single orchid and see if it kills it. Because honestly I wouldn't know, but I do know that when fertalizing it is good to neutralize an acidic to get it closer to neutral. Good Luck.